Research

Open AccessArticle

Anisotropic Hardening of TRIP780 Steel Sheet: Experiments and Analytical Modeling

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Materials 2023, 16(4), 1414; https://doi.org/10.3390/ma16041414 - 08 Feb 2023

Viewed by 413

Abstract

By combining experimental and theoretical models, this research investigates the anisotropic hardening behaviors of TRIP780 steel. The specimens of TRIP780 steel were subjected to uniaxial tensile and bulging tests under different loading conditions to obtain hardening data. The experimental results show that the [...] Read more.

By combining experimental and theoretical models, this research investigates the anisotropic hardening behaviors of TRIP780 steel. The specimens of TRIP780 steel were subjected to uniaxial tensile and bulging tests under different loading conditions to obtain hardening data. The experimental results show that the strength and plastic deformation of TRIP780 steel vary with the loading directions, which indicates that TRIP780 steel has anisotropy characteristics. In this paper, the dichotomous method is used to ensure the convexity of the Chen-coupled quadratic and non-quadratic (CQN) function. Comparing the predictions of the hardening behavior of the TRIP780 steel sheet by the Yld2000-2d, Stoughton-Yoon’2009 and Chen-CQN functions, the results show that the Chen-CQN function exhibits the advantages of simple numerical implementation and a more realistic prediction of yield stress compared to the former two, respectively. Comparing the prediction of Chen-CQN function with the experimental hardening data, the results show that the deviation between the experimental data and the experimental response given by the function is always within 3%, and this function maintains an accurate prediction under different stress states, indicating that the Chen-CQN yield function has accuracy and flexibility for the characterization of the yield surface of TRIP780 steel. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Large Cryogenic Magnetostriction Induced by Hydrostatic Pressure in MnCo_0.92Ni_0.08Si Alloy

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Materials 2023, 16(3), 1143; https://doi.org/10.3390/ma16031143 - 29 Jan 2023

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Abstract

Giant magnetostriction could be achieved in MnCoSi-based alloys due to the magneto-elastic coupling accompanied by the meta-magnetic transition. In the present work, the effects of hydrostatic pressure on magnetostrictive behavior in MnCo_0.92Ni_0.08Si alloy have been investigated. The saturation magnetostriction [...] Read more.

Giant magnetostriction could be achieved in MnCoSi-based alloys due to the magneto-elastic coupling accompanied by the meta-magnetic transition. In the present work, the effects of hydrostatic pressure on magnetostrictive behavior in MnCo_0.92Ni_0.08Si alloy have been investigated. The saturation magnetostriction (at 30,000 Oe) could be enhanced from 577 ppm to 5034 ppm by the hydrostatic pressure of 3.2 kbar at 100 K. Moreover, under a magnetic field of 20,000 Oe, the reversible magnetostriction was improved from 20 ppm to 2112 ppm when a hydrostatic pressure of 6.4 kbar was applied at 70 K. In all, it has been found that the magnetostrictive effect of the MnCo_0.92Ni_0.08Si compound is strongly sensitive to external hydrostatic pressure. This work proves that the MnCoSi-based alloys as a potential cryogenic magnetostrictive material can be modified through applied hydrostatic pressure. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Aging Behavior and Precipitates Analysis of Wrought Al-Si-Mg Alloy

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Fang Liu

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Fuxiao Yu

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Dazhi Zhao

Materials 2022, 15(22), 8194; https://doi.org/10.3390/ma15228194 - 18 Nov 2022

Viewed by 481

Abstract

Aging behavior of wrought Al-12.7Si-0.7 Mg alloy was investigated during isothermal aging at 180 °C. Two aging peaks were observed at 3 h and 8 h, respectively. To examine precipitate evolution during aging, the alloy’s microstructure in different aging states was investigated by [...] Read more.

Aging behavior of wrought Al-12.7Si-0.7 Mg alloy was investigated during isothermal aging at 180 °C. Two aging peaks were observed at 3 h and 8 h, respectively. To examine precipitate evolution during aging, the alloy’s microstructure in different aging states was investigated by regular and high-resolution transmission electron microscopy (TEM and HRTEM). The results revealed that the variation of mechanical properties is attributed to the combining effect of Si particles, the grain boundary, and the character of precipitates. The predominant precipitates’ type, size, and volume fraction vary as aging time increases. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Effect of High-Current Pulsed Electron Beam on Properties of Graphene-Modified Aluminum Titanium Carbide Composites

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Materials 2022, 15(22), 7879; https://doi.org/10.3390/ma15227879 - 08 Nov 2022

Cited by 1 | Viewed by 743

Abstract

High-current pulse electron beam (HCPEB) is an advanced surface modification technology developed in recent decades. This paper focuses on the effect of 0.3 wt.% graphene on the electrical conductivity and microhardness of HCPEB-treated Al-20TiC composites. The SEM results show that the titanium carbide [...] Read more.

High-current pulse electron beam (HCPEB) is an advanced surface modification technology developed in recent decades. This paper focuses on the effect of 0.3 wt.% graphene on the electrical conductivity and microhardness of HCPEB-treated Al-20TiC composites. The SEM results show that the titanium carbide was uniformly distributed in the aluminum matrix of the initial sample. Conversely, the graphene showed a small aggregation, and there were holes and cracks on the top surface of the sample. After HCPEB modification, the agglomeration of graphene gradually improved, and the number of surface pores reduced. The X-ray diffraction results show that after HCPEB treatment, the aluminum diffraction peak widened and shifted to a higher angle and the grain was significantly refined. Compared with the initial Al-20TiC composite samples, the conductivity of graphene-modified HCPEB-treated sample increased by 94.3%. The microhardness test results show that the microhardness of the graphene-modified HCPEB-treated sample increased by 18.4%, compared with the initial Al-20TiC composite samples. This enhancement of microhardness is attributed to the joint effects of fine grain strengthening, dispersion strengthening of the second phase, solution strengthening and dislocation strengthening. In brief, HCPEB has good application prospects for powder metallurgy in future. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Prediction of Magnetocaloric Effect Induced by Continuous Modulation of Exchange Interaction: A Monte Carlo Study

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Materials 2022, 15(21), 7777; https://doi.org/10.3390/ma15217777 - 04 Nov 2022

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Abstract

A magnetic-to-thermal energy conversion, derived from the continuous modulation of intrinsic exchange energy, is conceived and studied by performing Monte Carlo simulations. On the basis of thermodynamics and Weiss’s molecular field theories, we modified the Maxwell formula, where the magnetic entropy change (∆ [...] Read more.

A magnetic-to-thermal energy conversion, derived from the continuous modulation of intrinsic exchange energy, is conceived and studied by performing Monte Carlo simulations. On the basis of thermodynamics and Weiss’s molecular field theories, we modified the Maxwell formula, where the magnetic entropy change (∆S_M) is calculated by integrating the temperature derivative of magnetization under a continuously increasing exchange interaction, rather than an external magnetic field, from zero to a given value. For the conventional ∆S_M induced through increasing magnetic field, the ∆S_M maximum value is enhanced with increasing magnetic field, while the ∆S_M peak temperature is weakly influenced by the magnetic field. On the contrary, the ∆S_M induced by changing the exchange interaction is proportional to the exchange interaction while suppressed by a magnetic field. Another feature is that the relative cooling power calculated from the ∆S_M induced by changing the exchange interaction is fully independent of the magnetic field perspective for obtaining the magnetically stabilized self-converted refrigerants. The controlled variation of exchange interaction could be realized by partial substitution or the application of hydrostatic pressure to lower the cost of magnetic energy at no expense of magnetocaloric response, which opens an avenue to develop the practical and energy-saving devices of conversion from magnetic energy to thermal energy, highly extending the material species of the magnetocaloric effect. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Exploring Hydrogen Incorporation into the Nb₄AlC₃ MAX Phases: Ab Initio Calculations

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Materials 2022, 15(21), 7576; https://doi.org/10.3390/ma15217576 - 28 Oct 2022

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Abstract

The Nb₄AlC₃ MAX phase can be regarded as a TMC structure with stacking faults, which has great potential as a novel solid hydrogen storage material. Herein, we used ab initio calculations for understanding the hydrogen incorporation into Nb₄AlC [...] Read more.

The Nb₄AlC₃ MAX phase can be regarded as a TMC structure with stacking faults, which has great potential as a novel solid hydrogen storage material. Herein, we used ab initio calculations for understanding the hydrogen incorporation into Nb₄AlC₃ MAX phases, including equilibrium structural characteristics, energy changes, electronic structures, bonding characteristics, and diffusion paths. According to the calculated results, H has thermal stability in the interstice of the Nb-Al layer, and the most probable insertion site is an octahedron (3-site) composed of three Nb atoms and three Al atoms. When C vacancies are introduced, the Nb-C layer has a specific storage capacity for H. In addition, Al vacancies can also be used as possible sites for H incorporation. Moreover, the introduction of vacancies significantly increase the hydrogen storage capacity of the MAX phase. According to the electronic structure and bonding characteristics, the excellent hydrogen storage ability of the Nb₄AlC₃ structure may be due to the formation of ionic bonds between H and Nb/Al. It is worth noting that the H-Al bond in the 1-site is a covalent bond and an ionic bond key mixture. The linear synchronous transit optimization study shows that only H diffusion in Al vacancies is not feasible. In conclusion, the Nb-Al layer in Nb₄AlC₃ can provide favorable conditions for the continuous insertion and subsequent extraction of H, while the vacancy structure is more suitable for H storage. Our work provides solid theoretical results for understanding the hydrogen incorporation into Nb₄AlC₃ MAX phases that can be helpful for the design of advanced hydrogen storage materials. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Secondary Hardening of a High-N Ni-Free Stainless Steel

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Nathalie Siredey-Schwaller

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Materials 2022, 15(21), 7505; https://doi.org/10.3390/ma15217505 - 26 Oct 2022

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Abstract

High-N Ni-free stainless steels are used for their excellent mechanical properties combined with their high corrosion resistance, especially for biomedical applications. Even though it is well-known that secondary hardening during annealing after cold working has been observed in many materials, this phenomenon was [...] Read more.

High-N Ni-free stainless steels are used for their excellent mechanical properties combined with their high corrosion resistance, especially for biomedical applications. Even though it is well-known that secondary hardening during annealing after cold working has been observed in many materials, this phenomenon was not reported for these materials, one of the best known being Biodur108©, although numerous efforts have been made to increase its hardness. In this work, thermomechanical treatments at low temperature of cold-deformed Biodur108© were conducted to increase the hardness. Hardness as high as 830 Hv was obtained. For this material, the annealing of a deformed sample at intermediate temperature leads to a secondary hardening phenomenon. The mechanisms responsible for this secondary hardening were analyzed. It was found that for deformed samples, annealing at 575 °C leads to the formation of small Cr₂N precipitates along grain boundaries and sub-grain boundaries, and simultaneously with a new body-centered cubic (BCC) phase that possesses a super structure. The newly formed phases have sub-micrometric grain sizes. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Experiments and Modeling of Machined Spring Rotary Actuators with Shape Memory Alloys

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Materials 2022, 15(19), 6674; https://doi.org/10.3390/ma15196674 - 26 Sep 2022

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This paper presents a novel rotary actuator using an NiTi shape memory alloy machined spring (SMAMS). An analytical model is put forward to describe the relationship between the twist angle and temperature of SMAMSs under different applied torques. Following that, a numerical model [...] Read more.

This paper presents a novel rotary actuator using an NiTi shape memory alloy machined spring (SMAMS). An analytical model is put forward to describe the relationship between the twist angle and temperature of SMAMSs under different applied torques. Following that, a numerical model is developed to analyze the stress distributions and twist angle-torque responses of the SMAMS, tube, and spring of the circular cross-section. Thus, the advantages of the SMAMS over the other two rotary actuators are obtained. Moreover, experiments with SMAMSs are conducted to validate these models and study their mechanical responses. Results show that the SMAMS can be designed to have a larger twist angle than the cylindrical-type rotary actuators and to bear a larger torque than the wire-based-type rotary actuators, provided that the inner and outer diameter remains unchanged. Specifically, the maximum actuating twist angle of SMAMSs reaches 278.5°, and their maximum actuating torque is 0.312 N·m. The maximum two-way twist angle of SMAMSs reaches 171° at the pre-applied torque of 0.12 N·m. Moreover, the geometry is found to have a significant influence on the actuating capacity of SMAMSs. When the moments of inertia of SMAMS are 0.82 and 4.69, the corresponding torsion angles are 185.3° and 29.8°, respectively. In general, the SMAMSs with a larger moment of inertia can withstand a larger load. This work fills the gap between wire-based-type rotary actuators and cylindrical-type rotary actuators and is expected to expand the use for SMAs in the rotary actuator. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Electrical and Magnetic Transport Properties of Co₂VGa Half-Metallic Heusler Alloy

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Materials 2022, 15(17), 6138; https://doi.org/10.3390/ma15176138 - 04 Sep 2022

Cited by 2 | Viewed by 750

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This study performed a systematic experimental investigation into the structural, magnetic, and transport properties of the Co₂VGa Heusler alloy, which was theoretically predicted to exhibit half-metallic ferromagnetism. It has been experimentally found that the studied alloy has a relatively high-ordered L [...] Read more.

This study performed a systematic experimental investigation into the structural, magnetic, and transport properties of the Co₂VGa Heusler alloy, which was theoretically predicted to exhibit half-metallic ferromagnetism. It has been experimentally found that the studied alloy has a relatively high-ordered L2₁ cubic structure at room temperature and orders ferromagnetically below ~350 K. Interestingly, by fitting the electric transport data with the properly governing equations in two different temperature regions, the two-magnon scattering process (the

T^{9 / 2}

dependence) appears in the temperature range from 30 to 75 K. Moreover, the magnetoresistance effect changes from a negative value to a positive value when the temperature is below 100 K. Such experimental findings provide indirect evidence that the half-metallic nature of this alloy is retained only when the temperature is below 100 K. On the other hand, the magnetic transport measurements indicate that the anomalous Hall coefficient of this alloy increases when the temperature increases and reaches a relatively high value (~8.3 μΩ·cm/T) at 300 K due to its lower saturated magnetization. By analyzing the anomalous Hall resistivity scale with the longitudinal resistivity, it was also found that the anomalous Hall effect can be ascribed to the combined effect of extrinsic skew scattering and intrinsic Berry curvature, but the latter contribution plays a dominant role. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Strain Engineering in Ni-Co-Mn-Sn Magnetic Shape Memory Alloys: Influence on the Magnetic Properties and Martensitic Transformation

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Materials 2022, 15(17), 5889; https://doi.org/10.3390/ma15175889 - 26 Aug 2022

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Ni-Mn-Sn ferromagnetic shape memory alloys, which can be stimulated by an external magnetic field, exhibit a fast response and have aroused wide attention. However, the fixed and restricted working temperature range has become a challenge in practical application. Here, we introduced strain engineering, [...] Read more.

Ni-Mn-Sn ferromagnetic shape memory alloys, which can be stimulated by an external magnetic field, exhibit a fast response and have aroused wide attention. However, the fixed and restricted working temperature range has become a challenge in practical application. Here, we introduced strain engineering, which is an effective strategy to dynamically tune the broad working temperature region of Ni-Co-Mn-Sn alloys. The influence of biaxial strain on the working temperature range of Ni-Co-Mn-Sn alloy was systematically investigated by the ab initio calculation. These calculation results show a wide working temperature range (200 K) in Ni₁₄Co₂Mn₁₃Sn₃ FSMAs can be achieved with a slight strain from 1.5% to −1.5%, and this wide working temperature range makes Ni₁₄Co₂Mn₁₃Sn₃ meet the application requirements for both low-temperature and high-temperature (151–356 K) simultaneously. Moreover, strain engineering is demonstrated to be an effective method of tuning martensitic transformation. The strain can enhance the stability of the Ni₁₄Co₂Mn₁₃Sn₃ martensitic phase. In addition, the effects of strain on the magnetic properties and the martensitic transformation are explained by the electronic structure in Ni₁₄Co₂Mn₁₃Sn₃ FSMAs. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Ultrasonic Spray Pyrolysis Synthesis and Photoluminescence of LuAG:Ce Thin Films

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Materials 2022, 15(7), 2577; https://doi.org/10.3390/ma15072577 - 31 Mar 2022

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LuAG:Ce (Lu₃Al₅O₁₂:Ce) is one of the most important color converters in white lighting industry. Especially, LuAG:Ce film attracts more attention due to the outstanding advantages, such as the efficient heat dissipation, the saving of rare earth, and [...] Read more.

LuAG:Ce (Lu₃Al₅O₁₂:Ce) is one of the most important color converters in white lighting industry. Especially, LuAG:Ce film attracts more attention due to the outstanding advantages, such as the efficient heat dissipation, the saving of rare earth, and so on. Here, LuAG:Ce film on sapphire was successfully prepared by the ultrasonic spray pyrolysis process. The phase, microstructure and photoluminescence of LuAG:Ce films were investigated. LuAG:Ce films had a thickness of around 5 μm, which were well crystallized at 1000 °C in air atmosphere to form the typical garnet structure. Under the protection of CO atmosphere, increasing the annealing temperature greatly enhanced the photoluminescence performance. After annealing at 1500 °C for 5 h in CO atmosphere, 3.0 mol.% Ce³⁺ doped LuAG:Ce film exhibited the highest emission and excitation intensity. The emission intensity of 3.0 mol.% Ce³⁺ doped LuAG:Ce film annealed at 1500 °C in CO atmosphere increased up to five times, when compared with the best LuAG:Ce film annealed at 1000 °C in air atmosphere. The effects of Ce³⁺ doping concentration on the photoluminescence were also examined. As the Ce³⁺ doping concentration increased from 0.2 mol.% to 7.0 mol.%, the color of LuAG:Ce films changed from yellowish green to greenish yellow. When coupling the 3.0 mol.% Ce³⁺ doped LuAG:Ce film with a 0.5 W 450 nm blue laser, the formed device successfully emitted white light. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Quasi-Continuous Network Structure Greatly Improved the Anti-Arc-Erosion Capability of Ag/Y₂O₃ Electrical Contacts

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Materials 2022, 15(7), 2450; https://doi.org/10.3390/ma15072450 - 26 Mar 2022

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Abstract

Ag/Y₂O₃ has excellent potential to replace Ag/CdO as the environmentally friendly electrical contact material. Using spherical Y₂O₃ as the starting material, Ag/Y₂O₃ contacts with a quasi-continuous network structure were successfully fabricated by a low-energy [...] Read more.

Ag/Y₂O₃ has excellent potential to replace Ag/CdO as the environmentally friendly electrical contact material. Using spherical Y₂O₃ as the starting material, Ag/Y₂O₃ contacts with a quasi-continuous network structure were successfully fabricated by a low-energy ball milling treatment. The mean size of Y₂O₃ used ranged from 243 to 980 nm. Due to the differences in the size of Y₂O₃, Ag/Y₂O₃ contacts had different primitive microstructures, thereby exhibiting distinctive anti-arc-erosion capabilities. Ag/Y₂O₃ contact prepared using 243 nm Y₂O₃ showed the best anti-arc-erosion capability and the most outstanding electrical performance measures, such as low contact resistance, less mass transfer, and no failure up to 10⁵ cycle times. The quasi-continuous network structure formed in the micro-scale was responsible for the excellent electrical performance. The short distance between Y₂O₃ particles in the network promoted the cathode arc motion, and thus alleviated the localized erosion. The results obtained herein may inspire further attempts to design electrical contacts rationally. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Enhanced Magnetostrain in a <0 0 1>_A-Textured Ni_44.5Co_4.9Mn_37.5In_13.1 Alloy through Superelastic Training

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Materials 2022, 15(6), 2072; https://doi.org/10.3390/ma15062072 - 11 Mar 2022

Cited by 1 | Viewed by 1053

Abstract

Large magnetostrain can be demonstrated in Ni-Mn-X (X = In, Sn, Sb) meta-magnetic shape memory alloys by resuming the predeformed martensite through magnetic-field-induced reverse martensitic transformation. However, owing to the constraint from the self-accommodated microstructure and randomly distributed crystallographic orientation, spontaneous magnetostrain without [...] Read more.

Large magnetostrain can be demonstrated in Ni-Mn-X (X = In, Sn, Sb) meta-magnetic shape memory alloys by resuming the predeformed martensite through magnetic-field-induced reverse martensitic transformation. However, owing to the constraint from the self-accommodated microstructure and randomly distributed crystallographic orientation, spontaneous magnetostrain without predeformation in polycrystalline alloys remains low. Here, by combining microstructure texturing and superelastic training, enhanced spontaneous magnetostrain was achieved in a directionally solidified Ni_44.5Co_4.9Mn_37.5In_13.1 alloy with strong <0 0 1>_A preferred orientation. After superelastic training through cyclic compressive loading/unloading on the directionally solidified alloy, a large spontaneous magnetostrain of ~0.65% was obtained by applying a magnetic field of 5 T, showing great improvement when compared to that of the untrained situation, i.e., ~0.45%. Such enhanced magnetoresponse is attributed to the internal stress generated through superelastic training, which affects the variant distribution and the resultant output strain in association with the martensitic transformation. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Crystallography and Microstructure of 7M Martensite in Ni-Mn-Ga Thin Films Epitaxially Grown on (1 1

\bar{2}

0)-Oriented Al₂O₃ Substrate

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Materials 2022, 15(5), 1916; https://doi.org/10.3390/ma15051916 - 04 Mar 2022

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Abstract

Epitaxial Ni-Mn-Ga thin films have been extensively investigated, due to their potential applications in magnetic micro-electro-mechanical systems. It has been proposed that the martensitic phase in the <1 1 0>_A-oriented film is much more stable than that in the <1 0 [...] Read more.

Epitaxial Ni-Mn-Ga thin films have been extensively investigated, due to their potential applications in magnetic micro-electro-mechanical systems. It has been proposed that the martensitic phase in the <1 1 0>_A-oriented film is much more stable than that in the <1 0 0>_A-oriented film. Nevertheless, the magnetic properties, microstructural features, and crystal structures of martensite in such films have not been fully revealed. In this work, the <1 1 0>_A-oriented Ni_51.0Mn_27.5Ga_21.5 films with different thicknesses were prepared by epitaxially growing on Al₂O₃(1 1

\bar{2}

0) substrate by magnetron sputtering. The characterization by X-ray diffraction technique and transmission electron microscopy revealed that all the Ni_51.0Mn_27.5Ga_21.5 films are of 7M martensite at the ambient temperature, with their Type-I and Type-II twinning interfaces nearly parallel to the substrate surface. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Enhanced Photo-Fenton Activity of SnO₂/α-Fe₂O₃ Composites Prepared by a Two-Step Solvothermal Method

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Materials 2022, 15(5), 1743; https://doi.org/10.3390/ma15051743 - 25 Feb 2022

Cited by 1 | Viewed by 898

Abstract

The x-SnO₂/α-Fe₂O₃ (x = 0.04, 0.07, and 0.1) heterogeneous composites were successfully prepared via a two-step solvothermal method. These composites were systematically characterized by the X-ray diffraction technique, field emission scanning electron microscopy, an energy dispersive spectrometer, X-ray [...] Read more.

The x-SnO₂/α-Fe₂O₃ (x = 0.04, 0.07, and 0.1) heterogeneous composites were successfully prepared via a two-step solvothermal method. These composites were systematically characterized by the X-ray diffraction technique, field emission scanning electron microscopy, an energy dispersive spectrometer, X-ray photoelectron spectroscopy and a UV–visible spectrometer. It was found that SnO₂ nanoparticles were uniformly decorated on the surface of α-Fe₂O₃ particles in these heterogeneous composites. A comparative study of methylene blue (MB) photodegradation by α-Fe₂O₃ and x-SnO₂/α-Fe₂O₃ composites was carried out. All x-SnO₂/α-Fe₂O₃ composites showed higher MB photodegradation efficiency than α-Fe₂O₃. When x = 0.07, the MB photodegradation efficiency can reach 97% in 60 min. Meanwhile, the first-order kinetic studies demonstrated that the optimal rate constant of 0.07-SnO₂/α-Fe₂O₃ composite was 0.0537 min⁻¹, while that of pure α-Fe₂O₃ was only 0.0191 min⁻¹. The catalytic mechanism of MB photodegradation by SnO₂/α-Fe₂O₃ was examined. The SnO₂ can act as a sink and help the effective transfer of photo-generated electrons for decomposing hydrogen peroxide (H₂O₂) into active radicals. This work can provide a new insight into the catalytic mechanism of the photo-Fenton process. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Neighbor-Affected Orientation Rotation in the Grain Boundary Region

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Materials 2022, 15(3), 1059; https://doi.org/10.3390/ma15031059 - 29 Jan 2022

Cited by 1 | Viewed by 678

Abstract

Orientation rotation at grain boundary regions associated with neighboring orientations in Fe-3.0 wt.% Si non-oriented silicon steel has been investigated by crystal plastic simulation. Rotation tendency relative to a certain target orientation is evaluated by deviation angle variation. Taking ideal λ (<001>//ND, normal [...] Read more.

Orientation rotation at grain boundary regions associated with neighboring orientations in Fe-3.0 wt.% Si non-oriented silicon steel has been investigated by crystal plastic simulation. Rotation tendency relative to a certain target orientation is evaluated by deviation angle variation. Taking ideal λ (<001>//ND, normal direction) as the target orientation, the deviation angle of scattered {001} <uv0> orientations at grain boundary regions affected by neighboring orientations during rolling is calculated and verified by experimental measurements. The rotation tendency and rotation velocity field at grain boundary regions are significantly changed by neighboring orientations. According to the neighbor affected orientation rotation, the initial texture can be precisely designed to control the deformation texture at grain boundary regions. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Characterization and Calculation of the Dynamic Recrystallization Texture in Fe-3.0 Wt.% Si Alloy

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Materials 2022, 15(2), 517; https://doi.org/10.3390/ma15020517 - 10 Jan 2022

Cited by 1 | Viewed by 713

Abstract

High-temperature plane-strain compression tests were performed on Fe-3.0 wt.% Si alloy from 900 °C to 1150 °C at strain rates of 5 s⁻¹ to 1 s⁻¹, and the texture development from different initial textures was investigated by means of electron [...] Read more.

High-temperature plane-strain compression tests were performed on Fe-3.0 wt.% Si alloy from 900 °C to 1150 °C at strain rates of 5 s⁻¹ to 1 s⁻¹, and the texture development from different initial textures was investigated by means of electron backscattered diffraction. Dynamic recrystallization occurs by strain-induced boundary migration, and the evolutions of the microstructure and different texture components vary with the initial texture. The critical orientation boundary separating the weakened and enhanced texture components moves with the initial texture, and a quantitative relationship is established to represent the dependence of the critical Taylor factor on the instantaneous texture. A model is proposed to describe the dynamic recrystallization texture by incorporating the oriented nucleation probability with a variable critical Taylor factor. The present work could improve the accuracy of hot deformation texture prediction based on strain-induced boundary migration. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Complete Goss Secondary Recrystallization by Control of the Grain Size and Texture of Primary Recrystallization in Grain-Oriented Silicon Steel

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Materials 2021, 14(18), 5383; https://doi.org/10.3390/ma14185383 - 17 Sep 2021

Cited by 2 | Viewed by 1132

Abstract

Matrix microstructure and texture controlling is an important way to optimize Goss ({110}<001>) abnormal grain growth (AGG) in high magnetic induction grain-oriented silicon (Hi-B) steel during primary recrystallization. In the present work, a matrix with homogeneous grain size and favorable texture components was [...] Read more.

Matrix microstructure and texture controlling is an important way to optimize Goss ({110}<001>) abnormal grain growth (AGG) in high magnetic induction grain-oriented silicon (Hi-B) steel during primary recrystallization. In the present work, a matrix with homogeneous grain size and favorable texture components was obtained through two-stage normalized annealing followed by primary recrystallization. Furthermore, secondary recrystallization was performed for sharp Goss orientation by slow heating and purified annealing. It was found that plenty of island grains, which occurred and disappeared gradually, accompanied the process of AGG. Through analyzing the evolution of microstructure and texture, we realized that the formation of island grains was related to the large-size grains in matrix, and the elimination of that was attributed to the special grain boundaries which satisfied both coincident site lattice (CSL) and high-energy (HE) models. It was essential to control grain size and favorable orientations in matrix comprehensively for the high-efficient abnormal growing of sharp Goss orientation, through which excellent magnetic properties could be obtained simultaneously. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Large Low-Field Reversible Magnetocaloric Effect in Itinerant-Electron Hf_1−xTa_xFe₂ Alloys

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Materials 2021, 14(18), 5233; https://doi.org/10.3390/ma14185233 - 11 Sep 2021

Cited by 2 | Viewed by 987

Abstract

First-order isostructural magnetoelastic transition with large magnetization difference and controllable thermal hysteresis are highly desirable in the development of high-performance magnetocaloric materials used for energy-efficient and environmental-friendly magnetic refrigeration. Here, we demonstrate large magnetocaloric effect covering the temperature range from 325 K to [...] Read more.

First-order isostructural magnetoelastic transition with large magnetization difference and controllable thermal hysteresis are highly desirable in the development of high-performance magnetocaloric materials used for energy-efficient and environmental-friendly magnetic refrigeration. Here, we demonstrate large magnetocaloric effect covering the temperature range from 325 K to 245 K in Laves phase Hf_1−xTa_xFe₂ (x = 0.13, 0.14, 0.15, 0.16) alloys undergoing the magnetoelastic transition from antiferromagnetic (AFM) state to ferromagnetic (FM) state on decreasing the temperature. It is shown that with the increase of Ta content, the nature of AFM to FM transition is gradually changed from second-order to first-order. Based on the direct measurements, large reversible adiabatic temperature change (ΔT_ad) values of 2.7 K and 3.4 K have been achieved under a low magnetic field change of 1.5 T in the Hf_0.85Ta_0.15Fe₂ and Hf_0.84Ta_0.16Fe₂ alloys with the first-order magnetoelastic transition, respectively. Such remarkable magnetocaloric response is attributed to the rather low thermal hysteresis upon the transition as these two alloys are close to intermediate composition point of second-order transition converting to first-order transition. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Investigation on the Strengthening Mechanism of Flow Control Extrusion by Using Experiment and Numerical Simulation

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Guangshan Wu

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Yangqi Li

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Fei Chen

Materials 2021, 14(17), 5001; https://doi.org/10.3390/ma14175001 - 01 Sep 2021

Cited by 1 | Viewed by 1011

Abstract

Bimodal grain structure leads to high strength and strain hardening effect of metallic materials. In this study, an effective approach called flow control extrusion (FCE) is proposed to achieve heterostructures of pure copper. Compared with conventional extrusion (CE), FCE shows much stronger grain [...] Read more.

Bimodal grain structure leads to high strength and strain hardening effect of metallic materials. In this study, an effective approach called flow control extrusion (FCE) is proposed to achieve heterostructures of pure copper. Compared with conventional extrusion (CE), FCE shows much stronger grain refine ability and much weaker grain orientation concentration. The significant grain refinement and heterostructures depend on the severe shear strain from FCE. The heterostructures of sample subject to FCE transfer from bimodal structure to gradient structure with the decrease of temperature, as the grains in the surface of sample are all refined to ultrafine scale. Both these two heterostructures can realize the improvement of strength and strain hardening effect simultaneously. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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Open AccessArticle

Surface Treatment of Zn-Mn-Mg Alloys by Micro-Arc Oxidation in Silicate-Based Solutions with Different NaF Concentrations

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Materials 2021, 14(15), 4289; https://doi.org/10.3390/ma14154289 - 31 Jul 2021

Cited by 2 | Viewed by 1141

Abstract

Newly developed Zn-Mn-Mg alloys can be invoked as biomedical materials because of their excellent mechanical properties. However, the corrosion behavior of Zn-Mn-Mg alloys was still lacking in research. It had grown to be a hot research topic to improve the corrosion behavior of [...] Read more.

Newly developed Zn-Mn-Mg alloys can be invoked as biomedical materials because of their excellent mechanical properties. However, the corrosion behavior of Zn-Mn-Mg alloys was still lacking in research. It had grown to be a hot research topic to improve the corrosion behavior of Zn alloys by surface treatment to meet the application of degradable Zn alloys in biomedical applications. Micro arc oxidation (MAO) is a simple and effective method to improve the corrosion behavior of the alloy. MAO coatings were successfully prepared on the surface of Zn-Mn-Mg alloys by MAO in silicate-based solutions with different NaF concentrations. The microstructure and phase composition of MAO coatings prepared on Zn-Mn-Mg alloys with different NaF concentrations in the electrolyte was examined by a scanning electron microscope and X-ray diffraction. The results showed that the MAO coatings are porous and mainly composed of ZnO. With the increasing NaF concentration in the electrolyte, the average thickness increases. The distribution of the micro/nanopores was uniform, and the pore size ranged from the submicron scale to several micrometers after MAO treatment in the electrolyte containing different concentrations of NaF. Potential dynamic polarization curves and electrochemical impedance spectroscopy were employed to assess the corrosion behavior of MAO coatings in Hank’s solution. The highest corrosion rate can be achieved after MAO treatment, with an electrolyte concentration of 1.5 g/L NaF in Hank’s solution. These results indicated that MAO coating can accelerate the corrosion resistance of a Zn-Mn-Mg alloy. Full article

(This article belongs to the Special Issue Phase Transformation, Functional Properties, and Crystallography of Advanced Materials)

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