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3 pages, 153 KiB

Open AccessEditorial

Microstructure and Mechanical Properties of Structural Metals and Alloys

by Andrey Belyakov

Metals 2018, 8(9), 676; https://doi.org/10.3390/met8090676 - 29 Aug 2018

Cited by 4 | Viewed by 3290

Abstract

Mechanical properties of polycrystalline structural metals and alloys are significantly affected by their microstructures including phase content, grain/subgrain sizes, grain boundary distribution, dispersed particles, dislocation density, etc.[...] Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

Research

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13 pages, 13889 KiB

Open AccessArticle

Microstructure Evolution in Super Duplex Stainless Steels Containing σ-Phase Investigated at Low-Temperature Using In Situ SEM/EBSD Tensile Testing

by Christian Oen Paulsen, Runar Larsen Broks, Morten Karlsen, Jarle Hjelen and Ida Westermann

Metals 2018, 8(7), 478; https://doi.org/10.3390/met8070478 - 22 Jun 2018

Cited by 10 | Viewed by 5481

Abstract

An in situ scanning electron microscope (SEM) study was conducted on a super duplex stainless steel (SDSS) containing 0%, 5% and 10%

σ

-phase. The material was heat treated at 850 °C for 12 min and 15 min, respectively, to achieve the different [...] Read more.

An in situ scanning electron microscope (SEM) study was conducted on a super duplex stainless steel (SDSS) containing 0%, 5% and 10%

σ

-phase. The material was heat treated at 850 °C for 12 min and 15 min, respectively, to achieve the different amounts of

σ

-phase. The specimens were investigated at room temperature and at −40 °C. The microstructure evolution during the deformation process was recorded using electron backscatter diffraction (EBSD) at different strain levels. Both

σ

-phase and

χ

-phase were observed along the grain boundaries in the microstructure in all heat treated specimens. Cracks started to form after 3–4% strain and were always oriented perpendicular to the tensile direction. After the cracks formed, they were initially arrested by the matrix. At later stages of the deformation process, cracks in larger

σ

-phase constituents started to coalesce. When the tensile test was conducted at −40 °C, the ductility increased for the specimen without

σ

-phase, but with

σ

-phase present, the ductility was slightly reduced. With larger amounts of

σ

-phase present, however, an increase in tensile strength was also observed. With

χ

-phase present along the grain boundaries, a reduction of tensile strength was observed. This reduction seems to be related to

χ

-phase precipitating at the grain boundaries, creating imperfections, but not contributing towards the increase in strength. Compared to the effect of

σ

-phase, the low temperature is not as influential on the materials performance. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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10 pages, 2078 KiB

Open AccessFeature PaperArticle

Deformation Behavior of High-Mn TWIP Steels Processed by Warm-to-Hot Working

by Vladimir Torganchuk, Aleksandr M. Glezer, Andrey Belyakov and Rustam Kaibyshev

Metals 2018, 8(6), 415; https://doi.org/10.3390/met8060415 - 3 Jun 2018

Cited by 7 | Viewed by 3702

Abstract

The deformation behavior of 18%Mn TWIP steels (upon tensile tests) subjected to warm-to-hot rolling was analyzed in terms of Ludwigson-type relationship, i.e., σ = K₁·εⁿ¹ + exp(K₂ − n₂·ε). Parameters of K_i and n [...] Read more.

The deformation behavior of 18%Mn TWIP steels (upon tensile tests) subjected to warm-to-hot rolling was analyzed in terms of Ludwigson-type relationship, i.e., σ = K₁·εⁿ¹ + exp(K₂ − n₂·ε). Parameters of K_i and n_i depend on material and processing conditions and can be expressed by unique functions of inverse temperature. A decrease in the rolling temperature from 1373 K to 773 K results in a decrease in K₁ concurrently with n₁. Correspondingly, true stress approached a level of about 1750 MPa during tensile tests, irrespective of the previous warm-to-hot rolling conditions. On the other hand, an increase in both K₂ and n₂ with a decrease in the rolling temperature corresponds to an almost threefold increase in the yield strength and threefold shortening of the stage of transient plastic flow, which governs the duration of strain hardening and, therefore, manages plasticity. The change in deformation behavior with variation in the rolling temperature is associated with the effect of the processing conditions on the dislocation substructure, which, in turn, depends on the development of dynamic recovery and recrystallization during warm-to-hot rolling. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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13 pages, 5516 KiB

Open AccessArticle

Effect of the Martensitic Transformation on the Stamping Force and Cycle Time of Hot Stamping Parts

by Maider Muro, Garikoitz Artola, Anton Gorriño and Carlos Angulo

Metals 2018, 8(6), 385; https://doi.org/10.3390/met8060385 - 26 May 2018

Cited by 11 | Viewed by 4486

Abstract

Stamping dies perform two functions in the hot stamping process of body-in-white components. Firstly, they form the steel sheet into the desired shape and, secondly, they quench the steel at a cooling rate that leads to hardening by means of the austenite-γ to [...] Read more.

Stamping dies perform two functions in the hot stamping process of body-in-white components. Firstly, they form the steel sheet into the desired shape and, secondly, they quench the steel at a cooling rate that leads to hardening by means of the austenite-γ to martensite transformation. This microstructural change implies a volume expansion that should lead to a force peak in the press, which has yet to be detected in industrial practice. In this study, a set of hot stamping laboratory tests were performed on instrumented Al–Si-coated 22MnB5 steel flat formats to analyze the effect of the stamping pressure on the detection of the expected peak. Plotting the sheet temperature and pressure curves against time allowed us to identify and understand the conditions in which the force peak can be detected. These conditions occurred most favorably when the stamping pressure is below 5 MPa. It is thus possible to determine the exact moment at which the complete hardening transformation occurs by monitoring the local pressing force of the tool in areas where the pressure exerted on the metal format is below 5 MPa. This information can be applied to optimize the time needed to open the dies in terms of the complete martensitic transformation. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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8 pages, 3853 KiB

Open AccessArticle

Dissolution of M₂₃C₆ and New Phase Re-Precipitation in Fe Ion-Irradiated RAFM Steel

by Zheng Yang, Shuoxue Jin, Ligang Song, Weiping Zhang, Li You and Liping Guo

Metals 2018, 8(5), 349; https://doi.org/10.3390/met8050349 - 14 May 2018

Cited by 17 | Viewed by 5048

Abstract

The M₂₃C₆ precipitate plays a major role in preventing the sliding of the grain boundary and strengthens the matrix in the reduced-activation ferritic/martensic (RAFM) steel. However, its stability might be reduced under irradiation. The microstructural instability of the M₂₃ [...] Read more.

The M₂₃C₆ precipitate plays a major role in preventing the sliding of the grain boundary and strengthens the matrix in the reduced-activation ferritic/martensic (RAFM) steel. However, its stability might be reduced under irradiation. The microstructural instability of the M₂₃C₆ precipitates in the RAFM steels irradiated at 300 °C with Fe ions up to a peak dose of 40 dpa was investigated by transmission electron microscopy. A “Core/Shell” morphology was found for the pre-existing M₂₃C₆ and a large number of new small phases appeared in parallel near the periphery of the precipitates after irradiation. The loss of crystallinity of the M₂₃C₆ periphery due to the dissolution of carbon atoms into the interface (C-rich “Shell”) actually decreased the size of the Cr-rich “Core”. The new phase that formed around the pre-existing precipitates was M₆C (Fe₃W₃C), which was formed through the carbide transformation of M₂₃C₆ to M₆C. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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10 pages, 40503 KiB

Open AccessArticle

Study on the Control of Rare Earth Metals and Their Behaviors in the Industrial Practical Production of Q420q Structural Bridge Steel Plate

by Rensheng Chu, Yong Fan, Zhanjun Li, Jingang Liu, Na Yin and Ning Hao

Metals 2018, 8(4), 240; https://doi.org/10.3390/met8040240 - 5 Apr 2018

Cited by 11 | Viewed by 4270

Abstract

Rare earth (RE) addition can refine and change the shape/distribution of inclusions in steel to improve its strength and toughness. In this paper, the control of RE, specifically Ce and La, and their behaviors in the practical industrial production of high-strength structural steel [...] Read more.

Rare earth (RE) addition can refine and change the shape/distribution of inclusions in steel to improve its strength and toughness. In this paper, the control of RE, specifically Ce and La, and their behaviors in the practical industrial production of high-strength structural steel with 420 MPa yield strength were studied. In particular, the interactions between RE and Al, Nb, S, O were investigated, with the aim of improving the steel toughness and welding performance. The impact energy of the plate with RE is approximately 50 J higher than the regular plate without RE. The toughness of the plate from ladle furnace (LF) refining with RE addition is better than the one from Ruhrstahl and Hereaeus (RH) refining. The RE inclusions could induce the intragranular ferrite and refine the grain size to the preferred size. After welding at the heat input of 200 kJ/cm, the grain size at the heat affected zone was found to be the finest in the plate from the LF process with RE addition. Notably, the microstructure of ferrite was quasi-polygonal. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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15 pages, 5518 KiB

Open AccessArticle

Precipitation, Recrystallization, and Evolution of Annealing Twins in a Cu-Cr-Zr Alloy

by Xiaobo Chen, Feng Jiang, Jingyu Jiang, Pian Xu, Mengmeng Tong and Zhongqin Tang

Metals 2018, 8(4), 227; https://doi.org/10.3390/met8040227 - 1 Apr 2018

Cited by 28 | Viewed by 6428

Abstract

In this paper, the precipitation, recrystallization, and evolution of twins in Cu-Cr-Zr alloy strips were investigated. Tensile specimens were aged at three different temperatures for various times so as to bring the strips into every possible aging condition. The results show that the [...] Read more.

In this paper, the precipitation, recrystallization, and evolution of twins in Cu-Cr-Zr alloy strips were investigated. Tensile specimens were aged at three different temperatures for various times so as to bring the strips into every possible aging condition. The results show that the appropriate aging parameter for the 70% reduced cold-rolled alloy strips is 723 K for 240 min, with a tensile strength of 536 MPa and an electrical conductivity of 85.3% International Annealed Copper Standards (IACS) at the peak aged condition. The formation of fcc (face-centered cubic) ordered Cr-rich precipitates (β′) is an important factor influencing the significant improvement of properties near the peak aged condition. In terms of crystallographic orientation relationships, there are basically two types of β′ precipitates in the alloy. Beyond the Cr-rich precipitates (β′(I)) formed during the early aging stages, which mimic a cube-on-cube orientation relationship (OR) with the matrix, another Cr-rich precipitate (β′(II)) is observed in the peak aged condition. β′(II) is coherent with the matrix, with the following ORs: [111]_β′(II)//[100]_Cu, {02-2}_β′(II)//{02-2}_Cu and [011]_β′(II)//[211]_Cu, {200}_β′(II)//{-111}_Cu. These precipitates have a strong dislocation and grain boundary pinning effect, which hinder the dislocation movement and crystal boundary migration, and eventually delay recrystallization and enhance the recrystallization resistance of the peak aged strips. During the subsequent annealing process, the transition phase β′ gradually loses the coherence mismatch and grows into a larger equilibrium phase of chromium with a bcc (body-centered cubic) structure (β), resulting in the reduction of the pinning effect to dislocations and sub-grains, so that recrystallization occurs. Annealing twins are formed during the recrystallization process to release the deformation energy and to reduce the drive force for interface migration, eventually hindering grain growth. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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11 pages, 10383 KiB

Open AccessArticle

Characterization on the Microstructure Evolution and Toughness of TIG Weld Metal of 25Cr2Ni2MoV Steel after Post Weld Heat Treatment

by Xia Liu, Zhipeng Cai, Sida Yang, Kai Feng and Zhuguo Li

Metals 2018, 8(3), 160; https://doi.org/10.3390/met8030160 - 6 Mar 2018

Cited by 10 | Viewed by 4742

Abstract

The microstructure and toughness of tungsten inert gas (TIG) backing weld parts in low-pressure steam turbine welded rotors contribute significantly to the total toughness of the weld metal. In this study, the microstructure evolution and toughness of TIG weld metal of 25Cr2Ni2MoV steel [...] Read more.

The microstructure and toughness of tungsten inert gas (TIG) backing weld parts in low-pressure steam turbine welded rotors contribute significantly to the total toughness of the weld metal. In this study, the microstructure evolution and toughness of TIG weld metal of 25Cr2Ni2MoV steel low-pressure steam turbine welded rotor under different post-weld heat treatment (PWHT) conditions are investigated. The fractography and microstructure of weld metal after PWHT are characterized by optical microscope, SEM, and TEM, respectively. The Charpy impact test is carried out to evaluate the toughness of the weld. The optical microscope and SEM results indicate that the as-welded sample is composed of granular bainite, acicular ferrite and blocky martensite/austenite (M-A) constituent. After PWHT at 580 °C, the blocky M-A decomposes into ferrite and carbides. Both the number and size of precipitated carbides increase with holding time. The impact test results show that the toughness decreases dramatically after PWHT and further decreases with holding time at 580 °C. The precipitated carbides are identified as M₂₃C₆ carbides by TEM, which leads to the dramatic decrease in the toughness of TIG weld metal of 25Cr2Ni2MoV steel. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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13 pages, 8322 KiB

Open AccessArticle

Evolution of Microstructure and Mechanical Properties of a CoCrFeMnNi High-Entropy Alloy during High-Pressure Torsion at Room and Cryogenic Temperatures

by Sergey Zherebtsov, Nikita Stepanov, Yulia Ivanisenko, Dmitry Shaysultanov, Nikita Yurchenko, Margarita Klimova and Gennady Salishchev

Metals 2018, 8(2), 123; https://doi.org/10.3390/met8020123 - 10 Feb 2018

Cited by 45 | Viewed by 6913

Abstract

High-pressure torsion (HPT) is applied to a face-centered cubic CoCrFeMnNi high-entropy alloy at 293 and 77 K. Processing by HPT at 293 K produced a nanostructure consisted of (sub)grains of ~50 nm after a rotation for 180°. The microstructure evolution is associated with [...] Read more.

High-pressure torsion (HPT) is applied to a face-centered cubic CoCrFeMnNi high-entropy alloy at 293 and 77 K. Processing by HPT at 293 K produced a nanostructure consisted of (sub)grains of ~50 nm after a rotation for 180°. The microstructure evolution is associated with intensive deformation-induced twinning, and substructure development resulted in a gradual microstructure refinement. Deformation at 77 K produces non-uniform structure composed of twinned and fragmented areas with higher dislocation density then after deformation at room temperature. The yield strength of the alloy increases with the angle of rotation at HPT at room temperature at the cost of reduced ductility. Cryogenic deformation results in higher strength in comparison with the room temperature HPT. The contribution of Hall–Petch hardening and substructure hardening in the strength of the alloy in different conditions is discussed. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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9 pages, 1821 KiB

Open AccessArticle

Evaluation of Irradiation Hardening of P92 Steel under Ar Ion Irradiation

by Qingshan Li, Yinzhong Shen, Jun Zhu, Xi Huang and Zhongxia Shang

Metals 2018, 8(2), 94; https://doi.org/10.3390/met8020094 - 27 Jan 2018

Cited by 10 | Viewed by 4100

Abstract

P92 steel was irradiated with Ar ion up to 10 dpa at 200, 400, and 700 °C. The effect of Ar ion irradiation on hardness was investigated with nanoindentation tests and microstructure analyses. It was observed that irradiation-induced hardening occurred in the steel [...] Read more.

P92 steel was irradiated with Ar ion up to 10 dpa at 200, 400, and 700 °C. The effect of Ar ion irradiation on hardness was investigated with nanoindentation tests and microstructure analyses. It was observed that irradiation-induced hardening occurred in the steel after Ar ion irradiation at all three temperatures to 10 dpa. The steel exhibited significant hardening at 200 and 700 °C, and slight hardening at 400 °C under Ar ion irradiation. Difference in the magnitude of irradiation-induced hardening at different temperature in the steel is attributed to different changes in the microstructure of the steel that arose from the irradiation. Irradiation-induced hardening in the P92 steel irradiated at 200 °C is attributed to the occurrence of both dislocation loops and other fine irradiation defects during irradiation. Slight hardening in the steel irradiated at 400 °C mainly arises from the annihilation of defect clusters at this temperature. The occurrence of fine Ar bubbles with high number density during the Ar ion irradiation at 700 °C resulted in the significant hardening in the steel. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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12 pages, 6260 KiB

Open AccessArticle

Precipitation Stages and Reaction Kinetics of AlMgSi Alloys during the Artificial Aging Process Monitored by In-Situ Electrical Resistivity Measurement Method

by Hong He, Long Zhang, Shikang Li, Xiaodong Wu, Hui Zhang and Luoxing Li

Metals 2018, 8(1), 39; https://doi.org/10.3390/met8010039 - 11 Jan 2018

Cited by 13 | Viewed by 5409

Abstract

The precipitation process and reaction kinetics during artificial aging, precipitate microstructure, and mechanical properties after aging of AlMgSi alloys were investigated employing in-situ electrical resistivity measurement, Transmission Electron Microscopy (TEM) observation, and tensile test methods. Three aging stages in sequence, namely formation of [...] Read more.

The precipitation process and reaction kinetics during artificial aging, precipitate microstructure, and mechanical properties after aging of AlMgSi alloys were investigated employing in-situ electrical resistivity measurement, Transmission Electron Microscopy (TEM) observation, and tensile test methods. Three aging stages in sequence, namely formation of GP zones, transition from GP zones to β″ phase, transition from β″ to β′ phase, and coarsening of both phases, were clearly distinguished by the variation of the resistivity. It was discussed together with the mechanical properties and precipitate morphology evolution. Fast formation of GP zones and β″ phase leads to an obvious decrease of the resistivity and increase of the mechanical strength. The formation of β″ phase in the second stage, which contributes to the peak aging strength, has much higher reaction kinetics than reactions in the other two stages. All of these stages finished faster with higher reaction kinetics under higher temperatures, due to higher atom diffusion capacity. The results proved that the in-situ electrical resistivity method, as proposed in the current study, is a simple, effective, and convenient technique for real-time monitoring of the precipitation process of AlMgSi alloys. Its further application for industrial production and scientific research is also evaluated. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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13 pages, 8833 KiB

Open AccessArticle

Effect of Post Weld Heat Treatment on the Microstructure and Mechanical Properties of a Submerged-Arc-Welded 304 Stainless Steel

by Tae-Hoon Nam, Eunsol An, Byung Jun Kim, Sunmi Shin, Won-Seok Ko, Nokeun Park, Namhyun Kang and Jong Bae Jeon

Metals 2018, 8(1), 26; https://doi.org/10.3390/met8010026 - 2 Jan 2018

Cited by 31 | Viewed by 8250

Abstract

The present study is to investigate the effect of post heat treatment on the microstructures and mechanical properties of a submerged-arc-welded 304 stainless steel. The base material consisted of austenite and long strips of delta-ferrite surrounded by Cr-carbide, and the welds consisted of [...] Read more.

The present study is to investigate the effect of post heat treatment on the microstructures and mechanical properties of a submerged-arc-welded 304 stainless steel. The base material consisted of austenite and long strips of delta-ferrite surrounded by Cr-carbide, and the welds consisted of delta ferrite and austenite matrix. For the heat treatment at 850 °C or lower, Cr-carbides were precipitated in the weld metal resulting in the reduction of elongation. The strength, however, was slightly reduced despite the presence of Cr-carbides and this could possibly be explained by the relaxation of internal stress and the weakening of particle hardening. In the heat treatment at 1050 °C, the dissolution of Cr-carbide and disappearance of delta ferrite resulted in the lower yield strength and higher elongation partially assisted from deformation-induced martensitic transformation. Consequently, superior property in terms of fracture toughness was achieved by the heat treatment at 1050 °C, suggesting that the mechanical properties of the as-weld metal can be enhanced by controlling the post weld heat treatment. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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15 pages, 4719 KiB

Open AccessFeature PaperArticle

Effect of Tungsten on Creep Behavior of 9%Cr–3%Co Martensitic Steels

by Alexandra Fedoseeva, Nadezhda Dudova, Rustam Kaibyshev and Andrey Belyakov

Metals 2017, 7(12), 573; https://doi.org/10.3390/met7120573 - 18 Dec 2017

Cited by 21 | Viewed by 4695

Abstract

The effect of increasing tungsten content from 2 to 3 wt % on the creep rupture strength of a 3 wt % Co-modified P92-type steel was studied. Creep tests were carried out at a temperature of 650 °C under applied stresses ranging from [...] Read more.

The effect of increasing tungsten content from 2 to 3 wt % on the creep rupture strength of a 3 wt % Co-modified P92-type steel was studied. Creep tests were carried out at a temperature of 650 °C under applied stresses ranging from 100 to 220 MPa with a step of 20 MPa. It was found that an increase in W content from 2 to 3 wt % resulted in a +15% and +14% increase in the creep rupture strength in the short-term region (up to 10³ h) and long-term one (up to 10⁴ h), respectively. On the other hand, in the long-term creep region, the effect of W on creep strength diminished with increasing rupture time, up to complete disappearance at 10⁵ h, because of depletion of excess W from the solid solution in the form of precipitation of the Laves phase particles. An increase in W content led to the increased amount of Laves phase and rapid coarsening of these particles under long-term creep. The contribution of W to the enhancement of creep resistance has short-term character. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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12 pages, 9281 KiB

Open AccessFeature PaperArticle

Microstructure and Mechanical Properties of a High-Mn TWIP Steel Subjected to Cold Rolling and Annealing

by Alexander Kalinenko, Pavel Kusakin, Andrey Belyakov, Rustam Kaibyshev and Dmitri A. Molodov

Metals 2017, 7(12), 571; https://doi.org/10.3390/met7120571 - 18 Dec 2017

Cited by 14 | Viewed by 5812

Abstract

The structure–property relationship was studied in an Fe-18Mn-0.6C-1.5Al steel subjected to cold rolling to various total reductions from 20% to 80% and subsequent annealing for 30 min at temperatures of 673 to 973 K. The cold rolling resulted in significant strengthening of the [...] Read more.

The structure–property relationship was studied in an Fe-18Mn-0.6C-1.5Al steel subjected to cold rolling to various total reductions from 20% to 80% and subsequent annealing for 30 min at temperatures of 673 to 973 K. The cold rolling resulted in significant strengthening of the steel. The hardness increased from 1900 to almost 6000 MPa after rolling reduction of 80%. Recovery of cold worked microstructure developed during annealing at temperatures of 673 and 773 K, resulting in slight softening, which did not exceed 0.2. On the other hand, static recrystallization readily developed in the cold rolled samples with total reductions above 20% during annealing at 873 and 973 K, leading to fractional softening of about 0.8. The recrystallized grain size depended on annealing temperature and rolling reduction; namely, it decreased with a decrease in the temperature and an increase in the rolling reduction. The mean recrystallized grain size from approximately 1 to 8 μm could be developed depending on the rolling/annealing conditions. The recovered and fine grained recrystallized steel samples were characterized by improved strength properties. The yield strength of the recovered, recrystallized, and partially recrystallized steel samples could be expressed by a unique relationship taking into account the fractional contributions from dislocation and grain size strengthening into overall strength. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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12 pages, 3340 KiB

Open AccessArticle

The Effect of Eutectic Structure on the Creep Properties of Sn-3.0Ag-0.5Cu and Sn-8.0Sb-3.0Ag Solders

by Yujin Park, Jung-Hwan Bang, Chul Min Oh, Won Sik Hong and Namhyun Kang

Metals 2017, 7(12), 540; https://doi.org/10.3390/met7120540 - 3 Dec 2017

Cited by 11 | Viewed by 5925

Abstract

Solder joints are the main weak points of power modules used in harsh environments. For the power module of electric vehicles, the maximum operating temperature of a chip can reach 175 °C under driving conditions. Therefore, it is necessary to study the high-temperature [...] Read more.

Solder joints are the main weak points of power modules used in harsh environments. For the power module of electric vehicles, the maximum operating temperature of a chip can reach 175 °C under driving conditions. Therefore, it is necessary to study the high-temperature reliability of solder joints. This study investigated the creep properties of Sn-3.0Ag-0.5Cu (SAC305) and Sn-8.0Sb-3.0Ag (SSA8030) solder joints. The creep test was conducted at 175 and 190 °C with the application of 2.45 MPa. The SAC305 solder had superior creep properties to those of SSA8030 solder at 175 °C and at largely the same homologous temperature (

T_{H}

~0.91 for SAC305 and

T_{H}

~0.92 for SSA8030). Both solders had primary β-Sn and a eutectic mixture of β-Sn and Ag₃Sn. Compared to SSA8030, the SAC305 solder contained ~10% more eutectic structure and contained Ag₃Sn that was 3 times smaller and more round in shape. Furthermore, the SSA8030 solder precipitated SnSb in an elongated fiber shape (1–50 μm in size) after the creep test. Coarse and elongated Ag₃Sn and SnSb of the SSA8030 solder negatively affected crack propagation in the dislocation creep region and decreased the creep resistance. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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10 pages, 2962 KiB

Open AccessArticle

Effects of Strain Rate and Measuring Temperature on the Elastocaloric Cooling in a Columnar-Grained Cu₇₁Al_17.5Mn_11.5 Shape Memory Alloy

by Hui Wang, Haiyou Huang and Jianxin Xie

Metals 2017, 7(12), 527; https://doi.org/10.3390/met7120527 - 27 Nov 2017

Cited by 28 | Viewed by 5490

Abstract

Solid-state refrigeration technology based on elastocaloric effects (eCEs) is attracting more and more attention from scientists and engineers. The response speed of the elastocaloric materials, which relates to the sensitivity to the strain rate and measuring temperature, is a significant parameter to evaluate [...] Read more.

Solid-state refrigeration technology based on elastocaloric effects (eCEs) is attracting more and more attention from scientists and engineers. The response speed of the elastocaloric materials, which relates to the sensitivity to the strain rate and measuring temperature, is a significant parameter to evaluate the development of the elastocaloric material in device applications. Because the Cu-Al-Mn shape memory alloy (SMA) possesses a good eCE and a wide temperature window, it has been reported to be the most promising elastocaloric cooling material. In the present paper, the temperature changes (ΔT) induced by reversible martensitic transformation in a columnar-grained Cu₇₁Al_17.5Mn_11.5 SMA fabricated by directional solidification were directly measured over the strain rate range of 0.005–0.19 s⁻¹ and the measuring temperature range of 291–420 K. The maximum adiabatic ΔT of 16.5 K and a lower strain-rate sensitivity compared to TiNi-based SMAs were observed. With increasing strain rate, the ΔT value and the corresponding coefficient of performance (COP) of the alloy first increased, then achieved saturation when the strain rate reached 0.05 s⁻¹. When the measuring temperature rose, the ΔT value increased linearly while the COP decreased linearly. The results of our work provide theoretical reference for the design of elastocaloric cooling devices made of this alloy. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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12 pages, 4612 KiB

Open AccessArticle

Effect of High-Pressure Torsion on Structure and Microhardness of Ti/TiB Metal–Matrix Composite

by Sergey Zherebtsov, Maxim Ozerov, Nikita Stepanov, Margarita Klimova and Yulia Ivanisenko

Metals 2017, 7(11), 507; https://doi.org/10.3390/met7110507 - 16 Nov 2017

Cited by 14 | Viewed by 4822

Abstract

Effect of high-pressure torsion (HPT) at 400 °C on microstructure and microhardness of a Ti/TiB metal–matrix composite was studied. The starting material was produced by spark plasma sintering of a mixture of a pure Ti and TiB₂ (10 wt %) powders at [...] Read more.

Effect of high-pressure torsion (HPT) at 400 °C on microstructure and microhardness of a Ti/TiB metal–matrix composite was studied. The starting material was produced by spark plasma sintering of a mixture of a pure Ti and TiB₂ (10 wt %) powders at 1000 °C. The microstructure evolution during HPT was associated with an increase in dislocation density and substructure development that resulted in a gradual microstructure refinement of the Ti matrix and shortening/redistribution of TiB whiskers. After five revolutions, a nanostructure with (sub) grain size of ~30 nm was produced in Ti matrix. The microhardness increased with strain attaining the value ~520 HV after five revolutions. The contribution of different hardening mechanisms into the hardness of the Ti/TiB metal–matrix composite was quantitatively analyzed. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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12 pages, 16869 KiB

Open AccessArticle

Effect of Si and Zr on the Microstructure and Properties of Al-Fe-Si-Zr Alloys

by Anna Morozova, Anna Mogucheva, Dmitriy Bukin, Olga Lukianova, Natalya Korotkova, Nikolay Belov and Rustam Kaibyshev

Metals 2017, 7(11), 495; https://doi.org/10.3390/met7110495 - 11 Nov 2017

Cited by 20 | Viewed by 9063

Abstract

The effects of Si and Zr on the microstructure, microhardness and electrical conductivity of Al-Fe-Si-Zr alloys were studied. An increase in the Zr content over 0.3 wt. % leads to the formation of primary Al₃Zr inclusions and also decreases mechanical properties. [...] Read more.

The effects of Si and Zr on the microstructure, microhardness and electrical conductivity of Al-Fe-Si-Zr alloys were studied. An increase in the Zr content over 0.3 wt. % leads to the formation of primary Al₃Zr inclusions and also decreases mechanical properties. Therefore, the Zr content should not be more than 0.3 wt. %, although the smaller content is insufficient for the strengthening by the secondary Al₃Zr precipitates. The present results indicate that high content of Si significantly affects the hardness and electrical conductivity of the investigated alloys. However, the absence of Si led to the formation of harmful needle-shaped Al₃Fe particles in the microstructure of the investigated alloys after annealing. Therefore, the optimum amount of Si was 0.25–0.50 wt. % due to the formation of the Al₈Fe₂Si phase with the preferable platelet morphology. The maximum microhardness and strengthening effects in Al-1% Fe-0.25% Si-0.3% Zr were observed after annealing at 400–450 °C due to the formation of nanosized coherent Al₃Zr (L1₂) dispersoids. The effect of the increasing of the electrical conductivity can be explained by the decomposition of the solid solution. Thus, Al-1% Fe-0.25% Si-0.3% Zr alloy annealed at 450 °C has been studied in detail as the most attractive with respect to the special focus on transmission line applications. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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8 pages, 6485 KiB

Open AccessArticle

The Formation of Strong {100} Texture by Dynamic Strain-Induced Boundary Migration in Hot Compressed Ti-5Al-5Mo-5V-1Cr-1Fe Alloy

by Kai Li and Ping Yang

Metals 2017, 7(10), 412; https://doi.org/10.3390/met7100412 - 3 Oct 2017

Cited by 43 | Viewed by 5379

Abstract

The microstructure and texture evolution of Ti-5Al-5Mo-5V-1Cr-Fe alloy during hot compression were investigated by the electron backscatter diffraction technique. The results reveal that two main texture components containing <100> and <111> fiber textures form after the hot compression. The fraction of each component [...] Read more.

The microstructure and texture evolution of Ti-5Al-5Mo-5V-1Cr-Fe alloy during hot compression were investigated by the electron backscatter diffraction technique. The results reveal that two main texture components containing <100> and <111> fiber textures form after the hot compression. The fraction of each component is mainly controlled by deformation and strain rate. Dynamic strain-induced boundary migration (D-SIBM) is proved to be the reason that <100>-oriented grains grow towards <111>-oriented grains. The <100>-oriented grains coarsen with the increasing <100> texture intensity. Dynamic recrystallization (DRX) occurs under a low strain rate and large deformation. The DRX grains were detected by the method of grain orientation spread. The DRX grains reserve a <100> fiber texture similar to the deformation texture; however, DRX is not the main reason causing the formation of a strong <100> texture, due to its low volume fraction. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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11 pages, 3589 KiB

Open AccessArticle

Effect of Al₂O₃ Nanoparticles as Reinforcement on the Tensile Behavior of Al-12Si Composites

by Pan Ma, Yandong Jia, Prashanth Konda Gokuldoss, Zhishui Yu, Shanglei Yang, Jian Zhao and Chonggui Li

Metals 2017, 7(9), 359; https://doi.org/10.3390/met7090359 - 10 Sep 2017

Cited by 57 | Viewed by 7375

Abstract

Al₂O₃ nanoparticle-reinforced Al-12Si matrix composites were successfully fabricated by hot pressing and subsequent hot extrusion. The influence of weight fraction of Al₂O₃ particles on the microstructure, mechanical properties, and the corresponding strengthening mechanisms were investigated in detail. [...] Read more.

Al₂O₃ nanoparticle-reinforced Al-12Si matrix composites were successfully fabricated by hot pressing and subsequent hot extrusion. The influence of weight fraction of Al₂O₃ particles on the microstructure, mechanical properties, and the corresponding strengthening mechanisms were investigated in detail. The Al₂O₃ particles are uniformly distributed in the matrix, when 2 and 5 wt. % of Al₂O₃ particles were added to the Al-12Si matrix. Significant agglomeration can be found in composites with 10 wt. % addition of Al₂O₃ nanoparticles. The maximum hardness, the yield strength, and tensile strength were obtained for the composite with 5 wt. % Al₂O₃ addition, which showed an increase of about ~11%, 23%, and 26%, respectively, compared with the Al-12Si matrix. Meanwhile, the elongation increased to about ~30%. The contribution of different mechanisms including Orowan strengthening, thermal mismatch strengthening, and load transfer strengthening were analyzed. It was shown that the thermal mismatch strengthening has a more significant contribution to strengthening these composites than the Orowan and load transfer strengthening mechanisms. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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10 pages, 10721 KiB

Open AccessArticle

Emergence and Progression of Abnormal Grain Growth in Minimally Strained Nickel-200

by Olivia D. Underwood, Jonathan D. Madison and Gregory B. Thompson

Metals 2017, 7(9), 334; https://doi.org/10.3390/met7090334 - 30 Aug 2017

Cited by 8 | Viewed by 5839

Abstract

Grain boundary engineering (GBE) is a thermomechanical processing technique used to control the distribution, arrangement, and identity of grain boundary networks, thereby improving their mechanical properties. In both GBE and non-GBE metals, the phenomena of abnormal grain growth (AGG) and its contributing factors [...] Read more.

Grain boundary engineering (GBE) is a thermomechanical processing technique used to control the distribution, arrangement, and identity of grain boundary networks, thereby improving their mechanical properties. In both GBE and non-GBE metals, the phenomena of abnormal grain growth (AGG) and its contributing factors is still a subject of much interest and research. In a previous study, GBE was performed on minimally strained (ε < 10%), commercially pure Nickel-200 via cyclic annealing, wherein unique onset temperature and induced strain pairings were identified for the emergence of AGG. In this study, crystallographic segmentation of grain orientations from said experiments are leveraged in tandem with image processing to quantify growth rates for abnormal grains within the minimally strained regime. Advances in growth rates are shown to vary directly with initial strain content but inversely with initiating AGG onset temperature. A numeric estimator for advancement rates associated with AGG is also derived and presented. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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13 pages, 8517 KiB

Open AccessArticle

Study on Microstructure and Properties of Bimodal Structured Ultrafine-Grained Ferrite Steel

by Gang Niu, Huibin Wu, Da Zhang, Na Gong and Di Tang

Metals 2017, 7(8), 316; https://doi.org/10.3390/met7080316 - 18 Aug 2017

Cited by 15 | Viewed by 7554

Abstract

The objective of the study research was to obtain bimodal structured ultrafine-grained ferrite steel with outstanding mechanical properties and excellent corrosion resistance. The bimodal microstructure was fabricated by the cold rolling and annealing process of a dual-phase steel. The influences of the annealing [...] Read more.

The objective of the study research was to obtain bimodal structured ultrafine-grained ferrite steel with outstanding mechanical properties and excellent corrosion resistance. The bimodal microstructure was fabricated by the cold rolling and annealing process of a dual-phase steel. The influences of the annealing process on microstructure evolution and the mechanical properties of the cold-rolled dual-phase steel were investigated. The effect of bimodal microstructure on corrosion resistance was also studied. The results showed that the bimodal characteristic of ferrite steel was most apparent in cold-rolled samples annealed at 650 °C for 40 min. More importantly, due to the coordinated action of fine-grained strengthening, back-stress strengthening, and precipitation strengthening, the yield strength (517 MPa) of the bimodal microstructure improved significantly, while the total elongation remained at a high level of 26%. The results of corrosion experiments showed that the corrosion resistance of bimodal ferrite steel was better than that of dual-phase steel with the same composition. This was mainly because the Volta potential difference of bimodal ferrite steel was smaller than that of dual-phase steel, which was conducive to forming a protective rust layer. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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15 pages, 8741 KiB

Open AccessArticle

The Microstructures and Tensile Properties of As-Extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) Alloys

by Chaojie Che, Zhongyi Cai, Liren Cheng, Fanxing Meng and Zhen Yang

Metals 2017, 7(7), 281; https://doi.org/10.3390/met7070281 - 24 Jul 2017

Cited by 9 | Viewed by 4501

Abstract

The microstructures and tensile properties of as-cast and as-extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) alloys were systematically investigated by optical microscope, X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Numerous nanoscale [...] Read more.

The microstructures and tensile properties of as-cast and as-extruded Mg–4Sm–xZn–0.5Zr (x = 0, 1, 2, 3, 4 wt %) alloys were systematically investigated by optical microscope, X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Numerous nanoscale dynamic precipitates could be observed in the as-extruded alloys containing high content of Zn, and the nanoscale particles were termed as (Mg,Zn)₃Sm phase. Some basal disc-like precipitates were observed in as-extruded Mg–4Sm–4Zn–0.5Zr alloy, which were proposed to have a hexagonal structure with a = 0.556 nm. The dynamic precipitates effectively pinned the motions of DRXed (dynamic recrystallized) grain boundaries leading to an obvious reduction of DRXed grain size, and the tensile yield strength of as-extruded alloy was improved. The as-extruded Mg–4Sm–4Zn–0.5Zr alloy exhibits the best comprehensive mechanical properties at room temperature among all the alloys, and the yield strength, ultimate tensile strength and elongation are about 246 MPa, 273 MPa and 21% respectively. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Structural Metals and Alloys)

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