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Metals, Volume 5, Issue 2 (June 2015), Pages 484-1126

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Open AccessArticle Effects of Annealing on the Martensitic Transformation of Ni-Based Ferromagnetic Shape Memory Heusler Alloys and Nanoparticles
Metals 2015, 5(2), 484-503; doi:10.3390/met5020484
Received: 20 February 2015 / Revised: 11 March 2015 / Accepted: 12 March 2015 / Published: 25 March 2015
Cited by 6 | PDF Full-text (2528 KB) | HTML Full-text | XML Full-text
Abstract
We report on the effects of annealing on the martensitic phase transformation in the Ni-based Heusler system: Mn50Ni40Sn10 and Mn50Ni41Sn9 powder and Co50Ni21Ga32 nanoparticles. For the powdered Mn50Ni40Sn10 and Mn50Ni41Sn9 alloys, structural and magnetic measurements reveal that post-annealing decreases the martensitic transformation temperatures
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We report on the effects of annealing on the martensitic phase transformation in the Ni-based Heusler system: Mn50Ni40Sn10 and Mn50Ni41Sn9 powder and Co50Ni21Ga32 nanoparticles. For the powdered Mn50Ni40Sn10 and Mn50Ni41Sn9 alloys, structural and magnetic measurements reveal that post-annealing decreases the martensitic transformation temperatures and increases the transition hysteresis. This might be associated with a release of stress in the Mn50Ni40Sn10 and Mn50Ni41Sn9 alloys during the annealing process. However, in the case of Co50Ni21Ga32 nanoparticles, a reverse phenomenon is observed. X-ray diffraction analysis results reveal that the as-prepared Co50Ni21Ga32 nanoparticles do not show a martensitic phase at room temperature. Post-annealing followed by ice quenching, however, is found to trigger the formation of the martensitic phase. The presence of the martensitic transition is attributed to annealing-induced particle growth and the stress introduced during quenching. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2014)
Open AccessArticle An in situ Study of NiTi Powder Sintering Using Neutron Diffraction
Metals 2015, 5(2), 530-546; doi:10.3390/met5020530
Received: 27 February 2015 / Revised: 23 March 2015 / Accepted: 27 March 2015 / Published: 3 April 2015
Cited by 5 | PDF Full-text (1362 KB) | HTML Full-text | XML Full-text
Abstract
This study investigates phase transformation and mechanical properties of porous NiTi alloys using two different powder compacts (i.e., Ni/Ti and Ni/TiH2) by a conventional press-and-sinter means. The compacted powder mixtures were sintered in vacuum at a final temperature of
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This study investigates phase transformation and mechanical properties of porous NiTi alloys using two different powder compacts (i.e., Ni/Ti and Ni/TiH2) by a conventional press-and-sinter means. The compacted powder mixtures were sintered in vacuum at a final temperature of 1373 K. The phase evolution was performed by in situ neutron diffraction upon sintering and cooling. The predominant phase identified in all the produced porous NiTi alloys after being sintered at 1373 K is B2 NiTi phase with the presence of other minor phases. It is found that dehydrogenation of TiH2 significantly affects the sintering behavior and resultant microstructure. In comparison to the Ni/Ti compact, dehydrogenation occurring in the Ni/TiH2 compact leads to less densification, yet higher chemical homogenization, after high temperature sintering but not in the case of low temperature sintering. Moreover, there is a direct evidence of the eutectoid decomposition of NiTi at ca. 847 and 823 K for Ni/Ti and Ni/TiH2, respectively, during furnace cooling. The static and cyclic stress-strain behaviors of the porous NiTi alloys made from the Ni/Ti and Ni/TiH2 compacts were also investigated. As compared with the Ni/Ti sintered samples, the samplessintered from the Ni/TiH2 compact exhibited a much higher porosity, a higher close-to-total porosity, a larger pore size and lower tensile and compressive fracture strength. Full article
(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)
Open AccessArticle Research on Semisolid Microstructural Evolution of 2024 Aluminum Alloy Prepared by Powder Thixoforming
Metals 2015, 5(2), 547-564; doi:10.3390/met5020547
Received: 1 February 2015 / Revised: 25 March 2015 / Accepted: 27 March 2015 / Published: 3 April 2015
Cited by 17 | PDF Full-text (4745 KB) | HTML Full-text | XML Full-text
Abstract
A novel method, powder thixoforming, for net-shape forming of the particle-reinforced Aluminum matrix composites in semi-solid state has been proposed based on powder metallurgy combining with thixoforming technology. The microstructural evolution and phase transformations have been investigated during partial remelting of the 2024
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A novel method, powder thixoforming, for net-shape forming of the particle-reinforced Aluminum matrix composites in semi-solid state has been proposed based on powder metallurgy combining with thixoforming technology. The microstructural evolution and phase transformations have been investigated during partial remelting of the 2024 bulk alloy, prepared by cold pressing of atomized alloy powders to clarify the mechanisms of how the consolidated powders evolve into small and spheroidal primary particles available for thixoforming. The effect of heating temperature on the resulting semisolid microstructure has also been discussed. The results indicate that the microstructural evolution includes three stages—the initial rapid coarsening of the fine grains within the powders, the formation of continuous liquid layer on the primary particle surface (the original powder), and the final coarsening—that result from the phase transformations of θ→α, α→L, and α→L and L→α, respectively. The coarsening rate of the primary particles is low, and one original powder always evolves into one spheroidal particle with a continuous liquid layer surface. Properly raising the heating temperature is beneficial for obtaining an ideal semisolid microstructure. Full article
(This article belongs to the Special Issue Casting Alloy Design and Modification)
Open AccessArticle Influence of Zr Addition on Structure and Performance of Rare Earth Mg-Based Alloys as Anodes in Ni/MH Battery
Metals 2015, 5(2), 565-577; doi:10.3390/met5020565
Received: 18 February 2015 / Revised: 26 March 2015 / Accepted: 1 April 2015 / Published: 8 April 2015
Cited by 7 | PDF Full-text (610 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the substitution of Mg with Zr in La0.7Mg0.3(Ni0.85Co0.15)3.5 was carried out with the purpose of improving the electrochemical performances. The structural and hydrogen storage properties in both gas-solid reaction and the
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In this study, the substitution of Mg with Zr in La0.7Mg0.3(Ni0.85Co0.15)3.5 was carried out with the purpose of improving the electrochemical performances. The structural and hydrogen storage properties in both gas-solid reaction and the electrochemical system were systematically studied on La0.7(Mg0.3xZrx)(Ni0.85Co0.15)3.5 (x = 0.05, 0.1, 0.2, 0.3) alloys. Each tested alloy is composed of LaNi3 phase, LaNi5 phase and ZrNi3 phase with different phase abundances. The electrochemical studies indicated that all Zr-substituted anodes possessed a much higher cycling capacity retention than pristine La0.7Mg0.3(Ni0.85Co0.15)3.5. However, the maximum discharge capacity was reduced with the increase of Zr content. The potential-step tests showed that the diffusion of hydrogen atoms inside the anodes was decelerated after the introduction of Zr. Full article
Open AccessArticle Fatigue Behavior of an Ultrafine-Grained Al-Mg-Si Alloy Processed by High-Pressure Torsion
Metals 2015, 5(2), 578-590; doi:10.3390/met5020578
Received: 24 March 2015 / Revised: 30 March 2015 / Accepted: 31 March 2015 / Published: 10 April 2015
Cited by 4 | PDF Full-text (905 KB) | HTML Full-text | XML Full-text
Abstract
The paper presents the evaluation of the mechanical and fatigue properties of an ultrafine-grained (UFG) Al 6061 alloy processed by high-pressure torsion (HPT) at room temperature (RT). A comparison is made between the UFG state and the coarse-grained (CG) one subjected to the
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The paper presents the evaluation of the mechanical and fatigue properties of an ultrafine-grained (UFG) Al 6061 alloy processed by high-pressure torsion (HPT) at room temperature (RT). A comparison is made between the UFG state and the coarse-grained (CG) one subjected to the conventional aging treatment Т6. It is shown that HPT processing leads to the formation of the UFG microstructure with an average grain size of 170 nm. It is found that yield strength (σ0.2), ultimate tensile strength (σUTS) and the endurance limit (σf) in the UFG Al 6061 alloy are higher by a factor of 2.2, 1.8 and 2.0 compared to the CG counterpart subjected to the conventional aging treatment Т6. Fatigue fracture surfaces are analyzed, and the fatigue behavior of the material in the high cycle and low cycle regimes is discussed. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
Open AccessArticle Damage Behavior of Sintered Fiber Felts
Metals 2015, 5(2), 591-602; doi:10.3390/met5020591
Received: 1 October 2014 / Revised: 25 March 2015 / Accepted: 31 March 2015 / Published: 10 April 2015
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Abstract
The reduction of aircraft noise is important due to a rising number of flights and the growth of urban centers close to airports. During landing, a significant part of the noise is generated by flow around the airframe. To reduce that noise porous
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The reduction of aircraft noise is important due to a rising number of flights and the growth of urban centers close to airports. During landing, a significant part of the noise is generated by flow around the airframe. To reduce that noise porous trailing edges are investigated. Ideally, the porous materials should to be structural materials as well. Therefore, the mechanical properties and damage behavior are of major interest. The aim of this study is to show the change of structure and the damage behavior of sintered fiber felts, which are promising materials for porous trailing edges, under tensile loading using a combination of tensile tests and three dimensional computed tomography scans. By stopping the tensile test after a defined stress or strain and scanning the sample, it is possible to correlate structural changes and the development of damage to certain features in the stress-strain curve and follow the damage process with a high spatial resolution. Finally, the correlation between material structure and mechanical behavior is demonstrated. Full article
Open AccessArticle Estimation of Fatigue Crack Growth Rate for 7% Nickel Steel under Room and Cryogenic Temperatures Using Damage-Coupled Finite Element Analysis
Metals 2015, 5(2), 603-627; doi:10.3390/met5020603
Received: 10 February 2015 / Revised: 8 April 2015 / Accepted: 10 April 2015 / Published: 20 April 2015
PDF Full-text (2616 KB) | HTML Full-text | XML Full-text
Abstract
In this study, fatigue crack growth rates (FCGR) of 7% nickel steel at room and cryogenic temperatures were evaluated using damage-coupled finite element analysis (FEA). In order to perform the computational fatigue analysis effectively, methods for coupling damage to FEA are introduced and
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In this study, fatigue crack growth rates (FCGR) of 7% nickel steel at room and cryogenic temperatures were evaluated using damage-coupled finite element analysis (FEA). In order to perform the computational fatigue analysis effectively, methods for coupling damage to FEA are introduced and adopted. A hybrid method including the damage-coupled constitutive model and jump-in-cycles procedure was implemented into the ABAQUS user-defined material subroutine. Finally, the represented method was validated by comparing its results with the FCGR test results for 7% nickel steel under room and cryogenic temperatures. In particular, da/dN versusK and the crack length versus the number of cycles were compared. Full article
Open AccessArticle On the Effect of Pouring Temperature on Spheroidal Graphite Cast Iron Solidification
Metals 2015, 5(2), 628-647; doi:10.3390/met5020628
Received: 31 December 2014 / Revised: 26 March 2015 / Accepted: 27 March 2015 / Published: 20 April 2015
Cited by 2 | PDF Full-text (2501 KB) | HTML Full-text | XML Full-text
Abstract
This work is focused on the effect of pouring temperature on the thermal-microstructural response of an eutectic spheroidal graphite cast iron (SGCI). To this end, experiments as well as numerical simulations were carried out. Solidification tests in a wedge-like part were cast at
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This work is focused on the effect of pouring temperature on the thermal-microstructural response of an eutectic spheroidal graphite cast iron (SGCI). To this end, experiments as well as numerical simulations were carried out. Solidification tests in a wedge-like part were cast at two different pouring temperatures. Five specific locations exhibiting distinct cooling rates along the sample were chosen for temperature measurements and metallographic analysis to obtain the number and size of graphite nodules at the end of the process. The numerical simulations were performed using a multinodular-based model. Reasonably good numerical-experimental agreements were obtained for both the cooling curves and the graphite nodule counts. Full article
(This article belongs to the Special Issue Advances in Solidification Processing)
Open AccessCommunication Effects of Different Heat Treatment on Microstructure, Mechanical and Conductive Properties of Continuous Rheo-Extruded Al-0.9Si-0.6Mg (wt%) Alloy
Metals 2015, 5(2), 648-655; doi:10.3390/met5020648
Received: 11 February 2015 / Revised: 20 March 2015 / Accepted: 31 March 2015 / Published: 21 April 2015
Cited by 2 | PDF Full-text (769 KB) | HTML Full-text | XML Full-text
Abstract
Al-0.9Si-0.6Mg (wt%) alloy conductive wires were designed and produced by continuous rheo-extrusion process. The effects of different heat treatment on microstructure, mechanical and conductive properties of the wires were studied. Results show that, after T6 heat treatment, conductive property of the alloy increased
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Al-0.9Si-0.6Mg (wt%) alloy conductive wires were designed and produced by continuous rheo-extrusion process. The effects of different heat treatment on microstructure, mechanical and conductive properties of the wires were studied. Results show that, after T6 heat treatment, conductive property of the alloy increased while elongation decreased with the higher aging temperature and longer aging time. After T8 and T9 heat treatment, acicular strengthening phase β''-Mg2Si homogeneously precipitated, which effectively improved mechanical and conductive property of the alloy. The tensile strength, elongation and resistivity of T8 heat treated alloy reached 336 MPa, 13.7% and 29.3 nΩm respectively. After T9 heat treatment, the alloy’s tensile strength, elongation and resistivity was 338 MPa, 6.0% and 30.2 nΩ·m respectively. Full article
(This article belongs to the Special Issue Casting Alloy Design and Modification)
Open AccessArticle Development of Nanocrystalline 304L Stainless Steel by Large Strain Cold Working
Metals 2015, 5(2), 656-668; doi:10.3390/met5020656
Received: 29 March 2015 / Revised: 11 April 2015 / Accepted: 14 April 2015 / Published: 22 April 2015
Cited by 10 | PDF Full-text (1901 KB) | HTML Full-text | XML Full-text
Abstract
The microstructural changes leading to nanocrystalline structure development and the respective tensile properties were studied in a 304L stainless steel subjected to large strain cold rolling at ambient temperature. The cold rolling was accompanied by the development of deformation twinning and martensitic transformation.
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The microstructural changes leading to nanocrystalline structure development and the respective tensile properties were studied in a 304L stainless steel subjected to large strain cold rolling at ambient temperature. The cold rolling was accompanied by the development of deformation twinning and martensitic transformation. The latter readily occurred at deformation microshear bands, leading the martensite fraction to approach 0.75 at a total strain of 3. The deformation twinning followed by microshear banding and martensitic transformation promoted the development of nanocrystalline structure consisting of a uniform mixture of austenite and martensite grains with their transverse sizes of 120–150 nm. The developed nanocrystallites were characterized by high dislocation density in their interiors of about 3 × 1015 m−2 and 2 × 1015 m−2 in austenite and martensite, respectively. The development of nanocrystalline structures with high internal stresses led to significant strengthening. The yield strength increased from 220 MPa in the original hot forged state to 1600 MPa after cold rolling to a strain of 3. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
Open AccessArticle Effect of Milling Time and the Consolidation Process on the Properties of Al Matrix Composites Reinforced with Fe-Based Glassy Particles
Metals 2015, 5(2), 669-685; doi:10.3390/met5020669
Received: 27 March 2015 / Revised: 19 April 2015 / Accepted: 22 April 2015 / Published: 27 April 2015
Cited by 5 | PDF Full-text (1909 KB) | HTML Full-text | XML Full-text
Abstract
Al matrix composites reinforced with 40 vol% Fe50.1Co35.1Nb7.7B4.3Si2.8 glassy particles have been produced by powder metallurgy, and their microstructure and mechanical properties have been investigated in detail. Different processing routes (hot pressing and hot
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Al matrix composites reinforced with 40 vol% Fe50.1Co35.1Nb7.7B4.3Si2.8 glassy particles have been produced by powder metallurgy, and their microstructure and mechanical properties have been investigated in detail. Different processing routes (hot pressing and hot extrusion) are used in order to consolidate the composite powders. The homogeneous distribution of the glassy reinforcement in the Al matrix and the decrease of the particle size are obtained through ball milling. This has a positive effect on the hardness and strength of the composites. Mechanical tests show that the hardness of the hot pressed samples increases from 51–155 HV, and the strength rises from 220–630 MPa by extending the milling time from 1–50 h. The use of hot extrusion after hot pressing reduces both the strength and hardness of the composites: however, it enhances the plastic deformation significantly. Full article
(This article belongs to the Special Issue Metallic Glasses) Printed Edition available
Open AccessArticle Selective Laser Melting of Ti-45Nb Alloy
Metals 2015, 5(2), 686-694; doi:10.3390/met5020686
Received: 26 March 2015 / Revised: 16 April 2015 / Accepted: 21 April 2015 / Published: 27 April 2015
Cited by 11 | PDF Full-text (711 KB) | HTML Full-text | XML Full-text
Abstract
Ti-45Nb is one of the potential alloys that can be applied for biomedical applications as implants due to its low Young’s modulus. Ti-45Nb (wt.%) gas atomized powders were used to produce bulk samples by selective laser melting with three different parameter sets (energy
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Ti-45Nb is one of the potential alloys that can be applied for biomedical applications as implants due to its low Young’s modulus. Ti-45Nb (wt.%) gas atomized powders were used to produce bulk samples by selective laser melting with three different parameter sets (energy inputs). A β-phase microstructure consisting of elliptical grains with an enriched edge of titanium was observed by scanning electron microscopy and X-ray diffraction studies. The mechanical properties of these samples were evaluated using hardness and compression tests, which suggested that the strength of the samples increases with increasing energy input within the range considered. Full article
Open AccessArticle Martensitic Transformation in Ni-Mn-Sn-Co Heusler Alloys
Metals 2015, 5(2), 695-705; doi:10.3390/met5020695
Received: 1 March 2015 / Revised: 20 April 2015 / Accepted: 24 April 2015 / Published: 28 April 2015
Cited by 1 | PDF Full-text (1964 KB) | HTML Full-text | XML Full-text
Abstract
Thermal and structural austenite to martensite reversible transition was studied in melt spun ribbons of Ni50Mn40Sn5Co5, Ni50Mn37.5Sn7.5Co5 and Ni50Mn35Sn10Co5 (at. %)
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Thermal and structural austenite to martensite reversible transition was studied in melt spun ribbons of Ni50Mn40Sn5Co5, Ni50Mn37.5Sn7.5Co5 and Ni50Mn35Sn10Co5 (at. %) alloys. Analysis of X-ray diffraction patterns confirms that all alloys have martensitic structure at room temperature: four layered orthorhombic 4O for Ni50Mn40Sn5Co5, four layered orthorhombic 4O and seven-layered monoclinic 14M for Ni50Mn37.5Sn7.5Co5 and seven-layered monoclinic 14M for Ni50Mn35Sn5Co5. Analysis of differential scanning calorimetry scans shows that higher enthalpy and entropy changes are obtained for alloy Ni50Mn37.5Sn7.5Co5, whereas transition temperatures increases as increasing valence electron density. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2014)
Open AccessArticle Integral Steel Casting of Full Spade Rudder Trunk Carrier Housing for Supersized Container Vessels through Casting Process Engineering (Sekjin E&T)
Metals 2015, 5(2), 706-719; doi:10.3390/met5020706
Received: 2 February 2015 / Revised: 16 April 2015 / Accepted: 27 April 2015 / Published: 30 April 2015
Cited by 1 | PDF Full-text (1377 KB) | HTML Full-text | XML Full-text
Abstract
In casting steel for offshore construction, integral casted structures are superior to welded structures in terms of preventing fatigue cracks in the stress raisers. In this study, mold design and casting analysis were conducted for integral carrier housing. Casting simulation was used for
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In casting steel for offshore construction, integral casted structures are superior to welded structures in terms of preventing fatigue cracks in the stress raisers. In this study, mold design and casting analysis were conducted for integral carrier housing. Casting simulation was used for predicting molten metal flow and solidification during carrier housing casting, as well as the hot spots and porosity of the designed runner, risers, riser laggings, and the chiller. These predictions were used for deriving the final carrier housing casting plan, and a prototype was fabricated accordingly. A chemical composition analysis was conducted using a specimen sampled from a section of the prototype; the analytically obtained chemical composition agreed with the chemical composition of the existing carrier housing. Tensile and Charpy impact tests were conducted for determining the mechanical material properties. Carrier housing product after normalizing (920 °C/4.5 h, air-cooling) has 371 MPa of yield strength, 582 MPa of tensile strength, 33.4% of elongation as well as 64 J (0 °C) of impact energy. Full article
(This article belongs to the Special Issue Casting Alloy Design and Modification)
Open AccessArticle Production of Bulk Metallic Glasses by Severe Plastic Deformation
Metals 2015, 5(2), 720-729; doi:10.3390/met5020720
Received: 31 March 2015 / Revised: 20 April 2015 / Accepted: 23 April 2015 / Published: 30 April 2015
Cited by 5 | PDF Full-text (6190 KB) | HTML Full-text | XML Full-text
Abstract
The aim of this study was to show the possibility to produce bulk metallic glass with severe plastic deformation. High pressure torsion was used to consolidate Zr-based metallic glass powder and deform it further to weld the powder particles together. The produced samples
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The aim of this study was to show the possibility to produce bulk metallic glass with severe plastic deformation. High pressure torsion was used to consolidate Zr-based metallic glass powder and deform it further to weld the powder particles together. The produced samples were investigated with Scanning electron microscope (SEM), Transmission electron microscope (TEM), Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) to check if the specimens are fully dense and have an amorphous structure. The results show that the specimens remain amorphous during high pressure torsion and the density depends on the applied strain. Additional Vickers hardness measurements enable a comparison with literature and show for Zr-based metallic glass powder typical values (approximately 500 HV). Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
Open AccessArticle Ultrafine-Grained Austenitic Stainless Steels X4CrNi18-12 and X8CrMnNi19-6-3 Produced by Accumulative Roll Bonding
Metals 2015, 5(2), 730-742; doi:10.3390/met5020730
Received: 30 March 2015 / Revised: 24 April 2015 / Accepted: 4 May 2015 / Published: 7 May 2015
Cited by 2 | PDF Full-text (2056 KB) | HTML Full-text | XML Full-text
Abstract
Austenitic stainless steels X4CrNi18-12 and X8CrMnNi19-6-3 were processed by accumulative roll bonding (ARB). Both materials show an extremely high yield strength of 1.25 GPa accompanied by a satisfactory elongation to failure of up to 14% and a positive strain rate sensitivity after two
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Austenitic stainless steels X4CrNi18-12 and X8CrMnNi19-6-3 were processed by accumulative roll bonding (ARB). Both materials show an extremely high yield strength of 1.25 GPa accompanied by a satisfactory elongation to failure of up to 14% and a positive strain rate sensitivity after two ARB cycles. The strain-hardening rate of the austenitic steels reveals a stabilization of the stress-strain behavior during tensile testing. Especially for X8CrMnNi19-6-3, which has an elevated manganese content of 6.7 wt.%, necking is prevented up to comparatively high plastic strains. Microstructural investigations showed that the microstructure is separated into ultrafine-grained channel like areas and relatively larger grains where pronounced nano-twinning and martensite formation is observed. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
Open AccessArticle Ultrafine-Grained Precipitation Hardened Copper Alloys by Swaging or Accumulative Roll Bonding
Metals 2015, 5(2), 763-776; doi:10.3390/met5020763
Received: 30 March 2015 / Revised: 7 May 2015 / Accepted: 8 May 2015 / Published: 13 May 2015
Cited by 9 | PDF Full-text (994 KB) | HTML Full-text | XML Full-text
Abstract
There is an increasing demand in the industry for conductive high strength copper alloys. Traditionally, alloy systems capable of precipitation hardening have been the first choice for electromechanical connector materials. Recently, ultrafine-grained materials have gained enormous attention in the materials science community as
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There is an increasing demand in the industry for conductive high strength copper alloys. Traditionally, alloy systems capable of precipitation hardening have been the first choice for electromechanical connector materials. Recently, ultrafine-grained materials have gained enormous attention in the materials science community as well as in first industrial applications (see, for instance, proceedings of NANO SPD conferences). In this study the potential of precipitation hardened ultra-fine grained copper alloys is outlined and discussed. For this purpose, swaging or accumulative roll-bonding is applied to typical precipitation hardened high-strength copper alloys such as Corson alloys. A detailed description of the microstructure is given by means of EBSD, Electron Channeling Imaging (ECCI) methods and consequences for mechanical properties (tensile strength as well as fatigue) and electrical conductivity are discussed. Finally the role of precipitates for thermal stability is investigated and promising concepts (e.g. tailoring of stacking fault energy for grain size reduction) and alloy systems for the future are proposed and discussed. The relation between electrical conductivity and strength is reported. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
Open AccessArticle Manufacturing Ultrafine-Grained Ti-6Al-4V Bulk Rod Using Multi-Pass Caliber-Rolling
Metals 2015, 5(2), 777-789; doi:10.3390/met5020777
Received: 11 March 2015 / Revised: 27 April 2015 / Accepted: 30 April 2015 / Published: 15 May 2015
Cited by 2 | PDF Full-text (1401 KB) | HTML Full-text | XML Full-text
Abstract
Ultrafine-grained (UFG) Ti-6Al-4V alloy has attracted attention from the various industries due to its good mechanical properties. Although severe plastic deformation (SPD) processes can produce such a material, its dimension is generally limited to laboratory scale. The present work utilized the multi-pass caliber-rolling
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Ultrafine-grained (UFG) Ti-6Al-4V alloy has attracted attention from the various industries due to its good mechanical properties. Although severe plastic deformation (SPD) processes can produce such a material, its dimension is generally limited to laboratory scale. The present work utilized the multi-pass caliber-rolling process to fabricate Ti-6Al-4V bulk rod with the equiaxed UFG microstructure. The manufactured alloy mainly consisted of alpha phase and showed the fiber texture with the basal planes parallel to the rolling direction. This rod was large enough to be used in the industry and exhibited comparable tensile properties at room temperature in comparison to SPD-processed Ti-6Al-4V alloys. The material also showed good formability at elevated temperature due to the occurrence of superplasticity. Internal-variable analysis was carried out to measure the contribution of deformation mechanisms at elevated temperatures in the manufactured alloy. This revealed the increasing contribution of phase/grain-boundary sliding at 1073 K, which explained the observed superplasticity. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
Open AccessArticle Influence of Particulate Reinforcement and Equal-Channel Angular Pressing on Fatigue Crack Growth of an Aluminum Alloy
Metals 2015, 5(2), 790-801; doi:10.3390/met5020790
Received: 26 February 2015 / Revised: 22 April 2015 / Accepted: 12 May 2015 / Published: 18 May 2015
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Abstract
The fatigue crack growth behavior of unreinforced and particulate reinforced Al 2017 alloy, manufactured by powder metallurgy and additional equal-channel angular pressing (ECAP), is investigated. The reinforcement was done with 5 vol % Al2O3 particles with a size fraction of
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The fatigue crack growth behavior of unreinforced and particulate reinforced Al 2017 alloy, manufactured by powder metallurgy and additional equal-channel angular pressing (ECAP), is investigated. The reinforcement was done with 5 vol % Al2O3 particles with a size fraction of 0.2–2 µm. Our study presents the characterization of these materials by electron microscopy, tensile testing, and fatigue crack growth measurements. Whereas particulate reinforcement leads to a drastic decrease of the grain size, the influence of ECAP processing on the grain size is minor. Both reinforced conditions, with and without additional ECAP processing, exhibit reduced fatigue crack growth thresholds as compared to the matrix material. These results can be ascribed to the well-known effect of the grain size on the crack growth, since crack deflection and closure are directly affected. Despite their small grain size, the thresholds of both reinforced conditions depend strongly on the load ratio: tests at high load ratios reduce the fatigue threshold significantly. It is suggested that the strength of the particle-matrix-interface becomes the critical factor here and that the particle fracture at the interfaces dominates the failure behavior. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
Open AccessArticle Nanoreinforced Cast Al-Si Alloys with Al2O3, TiO2 and ZrO2 Nanoparticles
Metals 2015, 5(2), 802-821; doi:10.3390/met5020802
Received: 20 April 2015 / Revised: 10 May 2015 / Accepted: 11 May 2015 / Published: 20 May 2015
Cited by 8 | PDF Full-text (1750 KB) | HTML Full-text | XML Full-text
Abstract
This study presents a new concept of refining and enhancing the properties of cast aluminum alloys by adding nanoparticles. In this work, the effect of adding alumina (Al2O3), titanium dioxide (TiO2) and zirconia (ZrO2) nano-particles
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This study presents a new concept of refining and enhancing the properties of cast aluminum alloys by adding nanoparticles. In this work, the effect of adding alumina (Al2O3), titanium dioxide (TiO2) and zirconia (ZrO2) nano-particles (40 nm) to the aluminum cast alloy A356 as a base metal matrix was investigated. Alumina, titanium dioxide and zirconia nano-powders were stirred in the A356 matrix with different fraction ratios ranging from (0%–5%) by weight at variable stirring speeds ranging from (270, 800, 1500, 2150 rpm) in both the semisolid (600 °C) and liquid (700 °C) state using a constant stirring time of one minute. The cast microstructure exhibited change of grains from dendritic to spherical shape with increasing stirring speed. The fracture surface showed the presence of nanoparticles at the interdendritic spacing of the fracture surface and was confirmed with EDX analysis of these particles. The results of the study showed that the mechanical properties (strength, elongation and hardness) for the nanoreinforced castings using Al2O3, TiO2 and ZrO2 were enhanced for the castings made in the semi-solid state (600 °C) with 2 weight% Al2O3 and 3 weight% TiO2 or ZrO2 at 1500 rpm stirring speed. Full article
Open AccessArticle Effect of Sphere Properties on Microstructure and Mechanical Performance of Cast Composite Metal Foams
Metals 2015, 5(2), 822-835; doi:10.3390/met5020822
Received: 3 April 2015 / Revised: 2 May 2015 / Accepted: 6 May 2015 / Published: 20 May 2015
Cited by 4 | PDF Full-text (2121 KB) | HTML Full-text | XML Full-text
Abstract
Aluminum-steel composite metal foams (Al-S CMF) are manufactured using steel hollow spheres, with a variety of sphere carbon content, surface roughness, and wall porosity, embedded in an Aluminum matrix through gravity casting technique. The microstructural and mechanical properties of the material were studied
[...] Read more.
Aluminum-steel composite metal foams (Al-S CMF) are manufactured using steel hollow spheres, with a variety of sphere carbon content, surface roughness, and wall porosity, embedded in an Aluminum matrix through gravity casting technique. The microstructural and mechanical properties of the material were studied using scanning electron microscopy, energy dispersive spectroscopy, and quasi-static compressive testing. Higher carbon content and surface roughness in the sphere wall were responsible for an increase in formation of intermetallic phases which had a strengthening effect at lower strain levels, increasing the yield strength of the material by a factor of 2, while higher sphere wall porosity resulted in a decrease on the density of the material and improving its cushioning and ductility maintaining its energy absorption capabilities. Full article
Open AccessArticle A Mathematical Formulation to Estimate the Effect of Grain Refiners on the Ultimate Tensile Strength of Al-Zn-Mg-Cu Alloys
Metals 2015, 5(2), 836-849; doi:10.3390/met5020836
Received: 13 February 2015 / Accepted: 13 May 2015 / Published: 22 May 2015
Cited by 2 | PDF Full-text (847 KB) | HTML Full-text | XML Full-text
Abstract
In this study, the feed-forward (FF) neural networks (NNs) with back-propagation (BP) learning algorithm is used to estimate the ultimate tensile strength of unrefined Al-Zn-Mg-Cu alloys and refined the alloys by Al-5Ti-1B and Al-5Zr master alloys. The obtained mathematical formula is presented in
[...] Read more.
In this study, the feed-forward (FF) neural networks (NNs) with back-propagation (BP) learning algorithm is used to estimate the ultimate tensile strength of unrefined Al-Zn-Mg-Cu alloys and refined the alloys by Al-5Ti-1B and Al-5Zr master alloys. The obtained mathematical formula is presented in great detail. The designed NN model shows good agreement with test results and can be used to predict the ultimate tensile strength of the alloys. Additionally, the effects of scandium (Sc) and carbon (C) rates are investigated by using the proposed equation. It was observed that the tensile properties of Al-Zn-Mg-Cu alloys improved with the addition of 0.5 Sc and 0.01 C wt.%. Full article
Open AccessArticle Effect of Indium Content on the Microstructure, Mechanical Properties and Corrosion Behavior of Titanium Alloys
Metals 2015, 5(2), 850-862; doi:10.3390/met5020850
Received: 24 March 2015 / Accepted: 18 May 2015 / Published: 22 May 2015
Cited by 2 | PDF Full-text (2473 KB) | HTML Full-text | XML Full-text
Abstract
Ti-xIn (x = 0, 5, 10, 15 and 20 wt%) alloys were prepared to investigate the effect of indium on the microstructure, mechanical properties, and corrosion behavior of titanium with the aim of understanding the relationship between phase/microstructure and various
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Ti-xIn (x = 0, 5, 10, 15 and 20 wt%) alloys were prepared to investigate the effect of indium on the microstructure, mechanical properties, and corrosion behavior of titanium with the aim of understanding the relationship between phase/microstructure and various properties of Ti-xIn alloys. The Ti-xIn alloys exhibited a lamellar α-Ti structure at an indium content of up to 20 wt%. High-resolution TEM images of the Ti-xIn alloys revealed that all the systems contained a fine, acicular martensitic phase, which showed compositional fluctuations at the nanoscopic level. The mechanical properties and corrosion behavior of Ti-xIn alloys were sensitive to the indium content. The Vickers hardness increased as the In content increased because of solid solution strengthening. The Ti-xIn alloys exhibited superior oxidation resistance compared to commercially pure Ti (cp-Ti). Electrochemical results showed that the Ti-xIn alloys exhibited a similar corrosion resistance to cp-Ti. Among the alloys tested, Ti-10In showed a potential for use as a dental material. Full article
(This article belongs to the Special Issue Titanium Alloys)
Open AccessArticle Analysis of Magneto-Piezoelastic Anisotropic Materials
Metals 2015, 5(2), 863-880; doi:10.3390/met5020863
Received: 15 December 2014 / Accepted: 14 May 2015 / Published: 26 May 2015
PDF Full-text (727 KB) | HTML Full-text | XML Full-text
Abstract
The paper is concerned with the analysis of magneto-piezoelastic anistropic materials. Analytical modeling of magneto-piezoelastic materials is essential for the design and applications in the smart composite structures incorporating them as actuating and sensing constituents. It is shown that Green’s function method is
[...] Read more.
The paper is concerned with the analysis of magneto-piezoelastic anistropic materials. Analytical modeling of magneto-piezoelastic materials is essential for the design and applications in the smart composite structures incorporating them as actuating and sensing constituents. It is shown that Green’s function method is applicable to time harmonic magneto-elastic-piezoelectricity problems using the boundary integral technique, and the exact analytical solutions are obtained. As an application, a two-dimensional static plane-strain problem is considered to investigate the effect of magnetic field on piezoelectric materials. The closed-form analytical solutions are obtained for a number of boundary conditions for all components of the magneto-piezoelectric field. As a special case, numerical results are presented for two-dimensional static magneto-electroelastic field of a piezoelectric solid subjected to a concentrated line load and an electric charge. The numerical solutions are obtained for three different piezoelectric materials and they demonstrate a substantial dependence of the stress and electric field distribution on the constitutive properties and magnetic flux. Full article
Open AccessArticle Twinning-Detwinning Behavior during Cyclic Deformation of Magnesium Alloy
Metals 2015, 5(2), 881-890; doi:10.3390/met5020881
Received: 20 April 2015 / Revised: 12 May 2015 / Accepted: 18 May 2015 / Published: 26 May 2015
Cited by 7 | PDF Full-text (1101 KB) | HTML Full-text | XML Full-text
Abstract
In situ neutron diffraction has been used to examine the deformation mechanisms of a precipitation-hardened and extruded Mg-8.5wt.%Al alloy subjected to (i) compression followed by reverse tension (texture T1) and (ii) tension followed by reverse compression (texture T2). Two starting textures are used:
[...] Read more.
In situ neutron diffraction has been used to examine the deformation mechanisms of a precipitation-hardened and extruded Mg-8.5wt.%Al alloy subjected to (i) compression followed by reverse tension (texture T1) and (ii) tension followed by reverse compression (texture T2). Two starting textures are used: (1) as-extruded texture, T1, in which the basal pole of most grains is normal to the extrusion axis and a small portion of grains are oriented with the basal pole parallel to the extrusion axis; (2) a reoriented texture, T2, in which the basal pole of most grains is parallel to the extrusion axis. For texture T1, the onset of extension twinning corresponds well with the macroscopic elastic-plastic transition during the initial compression stage. The non-linear macroscopic stress/strain behavior during unloading after compression is more significant than during unloading after tension. For texture T2, little detwinning occurs after the initial tension stage, but almost all of the twinned volumes are detwinned during loading in reverse compression. Full article
(This article belongs to the Special Issue Metals Challenged by Neutron and Synchrotron Radiation)
Open AccessArticle Fatigue Behavior of Ultrafine-Grained Medium Carbon Steel with Different Carbide Morphologies Processed by High Pressure Torsion
Metals 2015, 5(2), 891-909; doi:10.3390/met5020891
Received: 21 March 2015 / Revised: 21 May 2015 / Accepted: 25 May 2015 / Published: 29 May 2015
Cited by 4 | PDF Full-text (1761 KB) | HTML Full-text | XML Full-text
Abstract
The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect
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The increased attention ultrafine grained (UFG) materials have received over the last decade has been inspired by their high strength in combination with a remarkable ductility, which is a promising combination for good fatigue properties. In this paper, we focus on the effect of different carbide morphologies in the initial microstructure on the fatigue behavior after high pressure torsion (HPT) treatment of SAE 1045 steels. The two initial carbide morphologies are spheroidized as well as tempered states. The HPT processing increased the hardness of the spheroidized and tempered states from 169 HV and 388 HV to a maximum of 511 HV and 758 HV, respectively. The endurance limit increased linearly with hardness up to about 500 HV independent of the carbide morphology. The fracture surfaces revealed mostly flat fatigue fracture surfaces with crack initiation at the surface or, more often, at non-metallic inclusions. Morphology and crack initiation mechanisms were changed by the severe plastic deformation. The residual fracture surface of specimens with spheroidal initial microstructures showed well-defined dimple structures also after HPT at high fatigue limits and high hardness values. In contrast, the specimens with a tempered initial microstructure showed rather brittle and rough residual fracture surfaces after HPT. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
Open AccessArticle Epitaxial Growth of Hard Ferrimagnetic Mn3Ge Film on Rhodium Buffer Layer
Metals 2015, 5(2), 910-919; doi:10.3390/met5020910
Received: 23 April 2015 / Revised: 15 May 2015 / Accepted: 21 May 2015 / Published: 2 June 2015
Cited by 3 | PDF Full-text (824 KB) | HTML Full-text | XML Full-text
Abstract
Mn\(_3\)Ge has a tetragonal Heusler-like D0\(_{22}\) crystal structure, exhibiting a large uniaxial magnetic anisotropy and small saturation magnetization due to its ferrimagnetic spin structure; thus, it is a hard ferrimagnet. In this report, epitaxial growth of a Mn\(_3\)Ge film on a Rh buffer
[...] Read more.
Mn\(_3\)Ge has a tetragonal Heusler-like D0\(_{22}\) crystal structure, exhibiting a large uniaxial magnetic anisotropy and small saturation magnetization due to its ferrimagnetic spin structure; thus, it is a hard ferrimagnet. In this report, epitaxial growth of a Mn\(_3\)Ge film on a Rh buffer layer was investigated for comparison with that of a film on a Cr buffer layer in terms of the lattice mismatch between Mn\(_3\)Ge and the buffer layer. The film grown on Rh had much better crystalline quality than that grown on Cr, which can be attributed to the small lattice mismatch. Epitaxial films of Mn\(_3\)Ge on Rh show somewhat small coercivity (\(H_{\rm c}\) = 12.6 kOe) and a large perpendicular magnetic anisotropy (\(K_{\rm u}\) = 11.6 Merg/cm\(^3\)), comparable to that of the film grown on Cr. Full article
(This article belongs to the Special Issue Manganese-based Permanent Magnets)
Open AccessArticle Mechanical and Structural Investigation of Porous Bulk Metallic Glasses
Metals 2015, 5(2), 920-933; doi:10.3390/met5020920
Received: 28 April 2015 / Revised: 20 May 2015 / Accepted: 25 May 2015 / Published: 2 June 2015
Cited by 6 | PDF Full-text (2959 KB) | HTML Full-text | XML Full-text
Abstract
The intrinsic properties of advanced alloy systems can be altered by changing their microstructural features. Here, we present a highly efficient method to produce and characterize structures with systematically-designed pores embedded inside. The fabrication stage involves a combination of photolithography and deep reactive
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The intrinsic properties of advanced alloy systems can be altered by changing their microstructural features. Here, we present a highly efficient method to produce and characterize structures with systematically-designed pores embedded inside. The fabrication stage involves a combination of photolithography and deep reactive ion etching of a Si template replicated using the concept of thermoplastic forming. Pt- and Zr-based bulk metallic glasses (BMGs) were evaluated through uniaxial tensile test, followed by scanning electron microscope (SEM) fractographic and shear band analysis. Compositional investigation of the fracture surface performed via energy dispersive X-ray spectroscopy (EDX), as well as Auger spectroscopy (AES) shows a moderate amount of interdiffusion (5 at.% maximum) of the constituent elements between the deformed and undeformed regions. Furthermore, length-scale effects on the mechanical behavior of porous BMGs were explored through molecular dynamics (MD) simulations, where shear band formation is observed for a material width of 18 nm. Full article
(This article belongs to the Special Issue Metallic Glasses) Printed Edition available
Open AccessCommunication Mechanical Behavior of Ultrafine Gradient Grain Structures Produced via Ambient and Cryogenic Surface Mechanical Attrition Treatment in Iron
Metals 2015, 5(2), 976-985; doi:10.3390/met5020976
Received: 31 March 2015 / Revised: 19 May 2015 / Accepted: 21 May 2015 / Published: 3 June 2015
Cited by 3 | PDF Full-text (741 KB) | HTML Full-text | XML Full-text
Abstract
Ambient and cryogenic surface mechanical attrition treatments (SMAT) are applied to bcc iron plate. Both processes result in significant surface grain refinement down to the ultrafine-grained regime; the cryogenic treatment results in a 45% greater grain size reduction. However, the refined region is
[...] Read more.
Ambient and cryogenic surface mechanical attrition treatments (SMAT) are applied to bcc iron plate. Both processes result in significant surface grain refinement down to the ultrafine-grained regime; the cryogenic treatment results in a 45% greater grain size reduction. However, the refined region is shallower in the cryogenic SMAT process. The tensile ductility of the grain size gradient remains low (<10%), in line with the expected behavior of the refined surface grains. Good tensile ductility in a grain size gradient requires the continuation of the gradient into an undeformed region. Full article
(This article belongs to the Special Issue Ultrafine-grained Metals) Printed Edition available
Open AccessArticle Hot Ductility Behavior of a Peritectic Steel during Continuous Casting
Metals 2015, 5(2), 986-999; doi:10.3390/met5020986
Received: 15 May 2015 / Revised: 25 May 2015 / Accepted: 27 May 2015 / Published: 3 June 2015
Cited by 1 | PDF Full-text (1527 KB) | HTML Full-text | XML Full-text
Abstract
Hot ductility properties of a peritectic steel for welded gas cylinders during continuous casting were studied by performing hot tensile tests at certain temperatures ranging from 1200 to 700 °C for some cooling rates by using Gleeble-3500 thermo-mechanical test and simulation machine in
[...] Read more.
Hot ductility properties of a peritectic steel for welded gas cylinders during continuous casting were studied by performing hot tensile tests at certain temperatures ranging from 1200 to 700 °C for some cooling rates by using Gleeble-3500 thermo-mechanical test and simulation machine in this study. The effects of cooling rate and strain rate on hot ductility were investigated and continuous casting process map (time-temperature-ductility) were plotted for this material. Reduction of area (RA) decreases and cracking susceptibility increases during cooling from solidification between certain temperatures depending on the cooling rate. Although the temperatures which fracture behavior change upon cooling during continuous casting may vary for different materials, it was found that the type of fracture was ductile at 1100 and 1050 °C; semi-ductile at 1000 °C, and brittle at 800 °C for the steel P245NB. There is a ductility trough between 1000 and 725 °C. The ductility trough gets slightly narrower as the cooling rate decreases. Full article
Open AccessArticle On Thermal Expansion and Density of CGI and SGI Cast Irons
Metals 2015, 5(2), 1000-1019; doi:10.3390/met5021000
Received: 30 April 2015 / Revised: 18 May 2015 / Accepted: 26 May 2015 / Published: 4 June 2015
Cited by 6 | PDF Full-text (1723 KB) | HTML Full-text | XML Full-text
Abstract
The thermal expansion and density of Compacted Graphite Iron (CGI) and Spheroidal Graphite Iron (SGI) were measured in the temperature range of 25–500 °C using push-rod type dilatometer. The coefficient of the thermal expansion (CTE) of cast iron can be expressed by the
[...] Read more.
The thermal expansion and density of Compacted Graphite Iron (CGI) and Spheroidal Graphite Iron (SGI) were measured in the temperature range of 25–500 °C using push-rod type dilatometer. The coefficient of the thermal expansion (CTE) of cast iron can be expressed by the following equation: CTE = 1.38 × 10−5 + 5.38 × 10−8 N − 5.85 × 10−7 G + 1.85 × 10−8 T − 2.41 × 10−6 RP/F − 1.28 × 10−8 NG − 2.97 × 10−7 GRP/F + 4.65 × 10−9 TRP/F + 1.08 × 10−7 G2 − 4.80 × 10−11 T2 (N: Nodularity, G: Area fraction of graphite (%), T: Temperature (°C), RP/F: Pearlite/Ferrite ratio in the matrix). Full article
(This article belongs to the Special Issue Casting Alloy Design and Modification)
Open AccessArticle Structure and Mössbauer Analysis of Melt-Spun Fe-Pd Ribbons Containing Ni and Co
Metals 2015, 5(2), 1020-1028; doi:10.3390/met5021020
Received: 15 April 2015 / Accepted: 25 May 2015 / Published: 5 June 2015
Cited by 1 | PDF Full-text (703 KB) | HTML Full-text | XML Full-text
Abstract
Fe68.45Pd28.21Co1.66Ni1.66 alloy in ribbon geometry was produced by melt spinning. The microstructure of the samples was examined using scanning electron microscopy. The structural identification of the as-spun ribbon sample and the annealed ones was performed by
[...] Read more.
Fe68.45Pd28.21Co1.66Ni1.66 alloy in ribbon geometry was produced by melt spinning. The microstructure of the samples was examined using scanning electron microscopy. The structural identification of the as-spun ribbon sample and the annealed ones was performed by means of X-ray diffraction. All the Bragg peaks were indexed based on an fcc type structure of (γ-Fe, Pd) phase with a lattice parameter a = 3.742 (3) Å. This result was proved by Mössbauer technique. The annealed ribbon at 600 °C shows an L10 ordered fct structure. An endothermic reaction at T = 358 °C followed by an exothermic one at 390 °C were observed on heating. These reactions were attributed to the Curie temperature of nickel and to the annihilation of an excess of quenched-in vacancies, respectively. Full article
(This article belongs to the Special Issue Shape Memory Alloys 2014)
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Open AccessArticle On the Stability of the Melt Jet Stream during Casting of Metallic Glass Wires
Metals 2015, 5(2), 1029-1044; doi:10.3390/met5021029
Received: 19 May 2015 / Revised: 31 May 2015 / Accepted: 2 June 2015 / Published: 8 June 2015
Cited by 2 | PDF Full-text (514 KB) | HTML Full-text | XML Full-text
Abstract
The factors that affect the stability of the melt stream during the casting of wire directly from the melt have been investigated. It is shown that the criticality of process parameters centres mostly on the forces imposed on the melt stream at confluence
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The factors that affect the stability of the melt stream during the casting of wire directly from the melt have been investigated. It is shown that the criticality of process parameters centres mostly on the forces imposed on the melt stream at confluence with the cooling water. The analysis of these forces indicated that the shear component of the disturbance is dependent on the ratio of the velocity of the melt stream (vm) to that of the cooling water (vw) in accord with results obtained from previous experiments. The role of oxide-forming elements in widening the process parameters range is attributed to the increased stability of the melt stream due to the additional shear force resistance offered by the solid oxide layer. The roles of Cr and Si oxides in stabilising the melt stream are confirmed by X-ray photoelectron spectroscopy (XPS) of wire indicating the presence of these oxides on fresh as-cast wires. Melt superheat and nozzle clearance distance are not strictly stream stability factors, but rather their role in glass formation prescribes optimal limits for fully amorphous wire. Full article
(This article belongs to the Special Issue Metallic Glasses) Printed Edition available
Open AccessArticle Submicron Particles during Macro- and Micro-Weldings Procedures in Industrial Indoor Environments and Health Implications for Welding Operators
Metals 2015, 5(2), 1045-1060; doi:10.3390/met5021045
Received: 29 April 2015 / Revised: 26 May 2015 / Accepted: 3 June 2015 / Published: 9 June 2015
Cited by 6 | PDF Full-text (849 KB) | HTML Full-text | XML Full-text
Abstract
One of the emerging risks in the engineering and electronic industries is the exposure of workers to ultrafine particles during (micro-)welding operations, i.e., processes used for joining two metal parts heated locally, which constitute the base metal, with or without addition of
[...] Read more.
One of the emerging risks in the engineering and electronic industries is the exposure of workers to ultrafine particles during (micro-)welding operations, i.e., processes used for joining two metal parts heated locally, which constitute the base metal, with or without addition of another metal which is the filler metal, melted between the edges to be joined. The process is accompanied by formation of metallic fumes arising from the molten metal as well as by the emission of metal fumes of variable composition depending on the alloys welded and fused. The aim of this paper is to investigate the number, concentration and size distribution of submicron particles produced by (micro-)welding processes. Particle number size distribution is continuously measured during (micro-)welding operations by means of two instruments, i.e., Fast Mobility Particle Sizer and Nanoparticle Surface Area Monitor. The temporal variation of the particle number size distribution across the peaks evidences the strong and fast-evolving contribution of nucleation mode particles: peak values are maintained for less than 10 s. The implication of such contribution on human health is linked to the high deposition efficiency of submicronic particles in the alveolar interstitial region of the human respiratory system, where gas exchange occurs. Full article
Open AccessArticle Synergic Role of Self-Interstitials and Vacancies in Indium Melting
Metals 2015, 5(2), 1061-1072; doi:10.3390/met5021061
Received: 21 April 2015 / Accepted: 11 June 2015 / Published: 16 June 2015
Cited by 4 | PDF Full-text (847 KB) | HTML Full-text | XML Full-text
Abstract
Precursor effects of indium melting have been investigated by means of Mechanical Spectroscopy (MS) and High Temperature X-ray Diffraction (HT-XRD). MS tests evidenced a sharp drop of dynamic modulus in the temperature range between 418 K and 429 K (melting point). At 429
[...] Read more.
Precursor effects of indium melting have been investigated by means of Mechanical Spectroscopy (MS) and High Temperature X-ray Diffraction (HT-XRD). MS tests evidenced a sharp drop of dynamic modulus in the temperature range between 418 K and 429 K (melting point). At 429 K, HT-XRD showed partial grain re-orientation, peak profile broadening, in particular in the lower part, and peak shift towards lower angles. Experimental results are consistent with density increase of self-interstitials and vacancies in the crystal lattice before melting. Self-interstitials and vacancies play a synergic role in the solid–liquid (S-L) transformation. The increase of self-interstitials over a temperature range of about 10 K before melting has the effect of weakening interatomic bonds (modulus drop) that favors the successive vacancy formation. Finally, the huge increase of vacancy concentration above 428 K leads to the collapse of crystal lattice (melting). Full article
Open AccessArticle Study on Dual Modification of Al-17%Si Alloys by Structural Heredity
Metals 2015, 5(2), 1112-1126; doi:10.3390/met5021112
Received: 30 April 2015 / Revised: 10 June 2015 / Accepted: 13 June 2015 / Published: 22 June 2015
Cited by 3 | PDF Full-text (2780 KB) | HTML Full-text | XML Full-text
Abstract
In this study, Al-17%Si alloys were dual modified by fine-grained structural materials (FSM) according to structural heredity. Microstructure and thermal analyses were undertaken to study the modification effect of the FSM master alloy on primary and eutectic Si. Primary Si is refined to
[...] Read more.
In this study, Al-17%Si alloys were dual modified by fine-grained structural materials (FSM) according to structural heredity. Microstructure and thermal analyses were undertaken to study the modification effect of the FSM master alloy on primary and eutectic Si. Primary Si is refined to a smaller size and eutectic Si is modified from needle-like to fibrous shape after FSM master alloy addition. The optimal content of FSM master alloy is 20% and the holding time is 15min. Finer FSM master alloy leads to finer Al-17%Si alloy microstructure and more area percentage of α-Al. DSC analyses results show that FSM master alloy can raise the precipitation temperatures of primary and eutectic Si, meanwhile it can reduce the latent heat of Si solidification process. Full article

Review

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Open AccessReview Understanding of the Structural Relaxation of Metallic Glasses within the Framework of the Interstitialcy Theory
Metals 2015, 5(2), 504-529; doi:10.3390/met5020504
Received: 31 January 2015 / Revised: 18 March 2015 / Accepted: 19 March 2015 / Published: 25 March 2015
Cited by 19 | PDF Full-text (1044 KB) | HTML Full-text | XML Full-text
Abstract
A review of the new approach to the understanding of the structural relaxation of metallic glasses based on the interstitialcy theory has been presented. The key hypothesis of this theory proposed by Granato consists of the statement that the thermodynamic properties of crystalline,
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A review of the new approach to the understanding of the structural relaxation of metallic glasses based on the interstitialcy theory has been presented. The key hypothesis of this theory proposed by Granato consists of the statement that the thermodynamic properties of crystalline, liquid and glassy states are closely related to the interstitial defects in the dumbbell (split) configuration, called also interstitialcies. It has been argued that structural relaxation of metallic glasses takes place through a change of the concentration of interstitialcy defects frozen-in from the melt upon glass production. Because of a strong interstitialcy-induced shear softening, the defect concentration can be precisely monitored by measurements of the unrelaxed shear modulus. Depending on the relation between the current interstitialcy concentration c and interstitialcy concentration in the metastable equilibrium, different types of structural relaxation (decreasing or increasing c) can be observed. It has been shown that this approach leads to a correct description of the relaxation kinetics at different testing conditions, heat effects occurring upon annealing, shear softening and a number of other structural relaxation-induced phenomena in metallic glasses. An intrinsic relation of these phenomena with the anharmonicity of the interatomic interaction has been outlined. A generalized form of the interstitialcy approach has been reviewed. Full article
(This article belongs to the Special Issue Metallic Glasses) Printed Edition available
Open AccessReview Processing and Properties of Aluminum and Magnesium Based Composites Containing Amorphous Reinforcement: A Review
Metals 2015, 5(2), 743-762; doi:10.3390/met5020743
Received: 27 January 2015 / Revised: 15 April 2015 / Accepted: 2 May 2015 / Published: 11 May 2015
Cited by 8 | PDF Full-text (1350 KB) | HTML Full-text | XML Full-text
Abstract
This review deals with the processing and properties of novel lightweight metal matrix composites. Conventionally, hard and strong ceramic particles are used as reinforcement to fabricate metal matrix composites (MMCs). However, the poor mechanical properties associated with the interfacial de-cohesion and undesirable reactions
[...] Read more.
This review deals with the processing and properties of novel lightweight metal matrix composites. Conventionally, hard and strong ceramic particles are used as reinforcement to fabricate metal matrix composites (MMCs). However, the poor mechanical properties associated with the interfacial de-cohesion and undesirable reactions at (ceramic) particle–(metallic) matrix interface represent major drawbacks. To overcome this limitation, metallic amorphous alloys (bulk metallic glass) have been recently identified as a promising alternative. Given the influential properties of amorphous metallic alloys, their incorporation is expected to positively influence the properties of light metal matrices when compared to conventional ceramic reinforcement. In view of this, a short account of the existing literature based on the processing and properties of Al- and Mg-matrix composites containing amorphous/bulk metallic glass (BMG) reinforcement is presented in this review. Full article
Open AccessReview Nanotoxicology of Metal Oxide Nanoparticles
Metals 2015, 5(2), 934-975; doi:10.3390/met5020934
Received: 8 April 2015 / Revised: 18 May 2015 / Accepted: 26 May 2015 / Published: 3 June 2015
Cited by 19 | PDF Full-text (1465 KB) | HTML Full-text | XML Full-text
Abstract
This review discusses recent advances in the synthesis, characterization and toxicity of metal oxide nanoparticles obtained mainly through biogenic (green) processes. The in vitro and in vivo toxicities of these oxides are discussed including a consideration of the factors important for safe use
[...] Read more.
This review discusses recent advances in the synthesis, characterization and toxicity of metal oxide nanoparticles obtained mainly through biogenic (green) processes. The in vitro and in vivo toxicities of these oxides are discussed including a consideration of the factors important for safe use of these nanomaterials. The toxicities of different metal oxide nanoparticles are compared. The importance of biogenic synthesized metal oxide nanoparticles has been increasing in recent years; however, more studies aimed at better characterizing the potent toxicity of these nanoparticles are still necessary for nanosafely considerations and environmental perspectives. In this context, this review aims to inspire new research in the design of green approaches to obtain metal oxide nanoparticles for biomedical and technological applications and to highlight the critical need to fully investigate the nanotoxicity of these particles. Full article
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Open AccessReview Mechanical Relaxation of Metallic Glasses: An Overview of Experimental Data and Theoretical Models
Metals 2015, 5(2), 1073-1111; doi:10.3390/met5021073
Received: 20 May 2015 / Revised: 11 June 2015 / Accepted: 12 June 2015 / Published: 19 June 2015
Cited by 13 | PDF Full-text (1945 KB) | HTML Full-text | XML Full-text
Abstract
Relaxation phenomena in glasses are a subject of utmost interest, as they are deeply connected with their structure and dynamics. From a theoretical point of view, mechanical relaxation allows one to get insight into the different atomic-scale processes taking place in the glassy
[...] Read more.
Relaxation phenomena in glasses are a subject of utmost interest, as they are deeply connected with their structure and dynamics. From a theoretical point of view, mechanical relaxation allows one to get insight into the different atomic-scale processes taking place in the glassy state. Focusing on their possible applications, relaxation behavior influences the mechanical properties of metallic glasses. This paper reviews the present knowledge on mechanical relaxation of metallic glasses. The features of primary and secondary relaxations are reviewed. Experimental data in the time and frequency domain is presented, as well as the different models used to describe the measured relaxation spectra. Extended attention is paid to dynamic mechanical analysis, as it is the most important technique allowing one to access the mechanical relaxation behavior. Finally, the relevance of the relaxation behavior in the mechanical properties of metallic glasses is discussed. Full article
(This article belongs to the Special Issue Metallic Glasses) Printed Edition available
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