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10 pages, 3541 KiB

Open AccessArticle

Effects of Vacancy Defects on Electrical and Optical Properties of ZnO/WSe₂ Heterostructure: First-Principles Study

by Xi Yong, Ao Wang, Lichuan Deng, Xiaolong Zhou and Jintao Li

Metals 2022, 12(11), 1975; https://doi.org/10.3390/met12111975 - 18 Nov 2022

Cited by 1 | Viewed by 1741

In this work, based on the first principles calculation of density functional theory (DFT), we studied the band structure changes of monolayer ZnO and ZnO/WSe₂ before and after vacancy generation, and systematically studied the vacancy formation energy, band structure, density of states, [...] Read more.

In this work, based on the first principles calculation of density functional theory (DFT), we studied the band structure changes of monolayer ZnO and ZnO/WSe₂ before and after vacancy generation, and systematically studied the vacancy formation energy, band structure, density of states, electronic density difference and optical properties of ZnO/WSe₂ heterostructure before and after vacancy generation. The results show that the band structures of ZnO, WSe_2, and ZnO/WSe₂ heterostructure are changed after the formation of Zn, O, W, and Se vacancies. The bandgap of the ZnO/WSe₂ heterostructure can be effectively controlled, the transition from direct to indirect bandgap semiconductor will occur, and the heterostructure will show metallic properties. The optical properties of heterostructure have also changed significantly, and the absorption capacity of heterostructure to infrared light has been greatly increased with red shift and blue shift respectively. The generation of vacancy changes the electrical and optical properties of ZnO/WSe₂ heterostructure, which provides a feasible strategy for adjusting the photoelectric properties of two-dimensional optoelectronic nano devices and has good potential and broad application prospects. Full article

(This article belongs to the Special Issue Preparation, Properties, Computational Simulations of Precious and Rare Metal Materials and Their Compounds)

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13 pages, 4867 KiB

Open AccessArticle

Mechanical Properties and Microstructural Evolution of Ti-25Nb-6Zr Alloy Fabricated by Spark Plasma Sintering at Different Temperatures

by Qing Zhu, Peng Chen, Qiushuo Xiao, Fengxian Li, Jianhong Yi, Konda Gokuldoss Prashanth and Jürgen Eckert

Metals 2022, 12(11), 1824; https://doi.org/10.3390/met12111824 - 27 Oct 2022

Cited by 1 | Viewed by 1484

Abstract

High-energy ball milling and spark plasma sintering (SPS) are used to create high-strength Ti-25Nb-6Zr biomedical alloys with β structures. The Ti-25Nb-6Zr alloy microstructure and mechanical properties were examined as a function of the sintering temperatures. The results showed that as the sintering temperature [...] Read more.

High-energy ball milling and spark plasma sintering (SPS) are used to create high-strength Ti-25Nb-6Zr biomedical alloys with β structures. The Ti-25Nb-6Zr alloy microstructure and mechanical properties were examined as a function of the sintering temperatures. The results showed that as the sintering temperature was raised, the densification process was expedited, and the comprehensive mechanical characteristics increased at first, then dropped slightly. Moreover, under high temperatures, the fracture morphology of the Ti-25Nb-6Zr biomedical alloys exhibited more dimples, indicating enhanced plasticity of the material. Evaluating the mechanical properties of the Ti-25Nb-6Zr biomedical alloy sintered at 1623 K indicated a high compressive strength of 1678.4 ± 5 MPa and an elongation of 12.4 ± 0.5%. The strengthening mechanisms are discussed in terms of the formation and distribution of bcc-Ti in the matrix as well as the homogeneous distribution of Nb and Zr. This research presents a new method for fabricating Ti-25Nb-6Zr biomedical alloys with high strength and low modulus values. The theoretical grounds for the development of high-performance Ti-Nb-Zr alloys will be laid by detailed research of this technology and its strengthening mechanisms. Full article

(This article belongs to the Special Issue Preparation, Properties, Computational Simulations of Precious and Rare Metal Materials and Their Compounds)

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17 pages, 3632 KiB

Open AccessArticle

Effects of Vacancies on the Structural, Elastic, Electronic and Thermodynamic Properties of C11_b-VSi₂ by First-Principles Calculations

by Shan Xu, Yonghua Duan, Mingjun Peng and Li Shen

Metals 2022, 12(10), 1625; https://doi.org/10.3390/met12101625 - 28 Sep 2022

Cited by 7 | Viewed by 1579

Abstract

The effects of V and Si vacancies on structural stability, elastic properties, brittleness-toughness transition, Debye temperature and electronic properties of tetragonal C11_b-VSi₂ are investigated using the first-principles calculations. The vacancy formation energy and phonon dispersions confirm that perfect C11_b [...] Read more.

The effects of V and Si vacancies on structural stability, elastic properties, brittleness-toughness transition, Debye temperature and electronic properties of tetragonal C11_b-VSi₂ are investigated using the first-principles calculations. The vacancy formation energy and phonon dispersions confirm that perfect C11_b-VSi₂ and C11_b-VSi₂ with different atomic vacancies are thermodynamically and dynamically stable. The C11_b-VSi₂ with V-atom vacancies is more stable than that with Si-atom vacancies. The introduction of different atomic vacancies enhances the elastic modulus and its anisotropy of C11_b-VSi₂. The electron density difference and densities of state of perfect VSi₂ and VSi₂ with different vacancies are calculated, and the chemical bonding properties of perfect VSi₂ and VSi₂ with vacancies are discussed and analyzed. Additionally, the results show that the chemical bond strength of VSi₂ is enhanced by the introduction of vacancies. Finally, Debye temperatures of perfect VSi₂ and VSi₂ with vacancies are also calculated. Full article

(This article belongs to the Special Issue Preparation, Properties, Computational Simulations of Precious and Rare Metal Materials and Their Compounds)

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11 pages, 2157 KiB

Open AccessArticle

Achieving Tunable Microwave Absorbing Properties by Phase Control of NiCoMnSn Alloy Flakes

by Xiaogang Sun, Jian Xu, Lian Huang, Daitao Kuang, Jinrong Liu, Guanxi Wang, Qifei Zhang and Yonghua Duan

Metals 2022, 12(9), 1542; https://doi.org/10.3390/met12091542 - 18 Sep 2022

Cited by 1 | Viewed by 1711

Abstract

Microwave absorption performance of metal alloys are highly dependent on their phase structures. However, the phase control of Ni–Mn-based alloys to achieve effective microwave absorption properties has been rarely reported. In this work, Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes [...] Read more.

Microwave absorption performance of metal alloys are highly dependent on their phase structures. However, the phase control of Ni–Mn-based alloys to achieve effective microwave absorption properties has been rarely reported. In this work, Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes were fabricated by balling milling method, and the contents of γ phase in the flakes were tuned by the subsequent heat treatment process. The as-fabricated Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes exhibited excellent tunable microwave absorption by control of their phase structures. The optimal reflection loss was lower, up to −56.4 dB at 8.8 GHz, and was achieved at a single thickness of 2.0 mm. This can be attributed to the optimal structure of Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes by phase control, and thus achieving improved attenuation property and impedance matching. This study proved Ni₄₃Co₇Mn₃₉Sn₁₁ alloy flakes should be a promising microwave absorption material. It is also demonstrated that phase control is an effected strategy for optimal microwave absorption properties of metal alloys and may have some reference value for related studies. Full article

(This article belongs to the Special Issue Preparation, Properties, Computational Simulations of Precious and Rare Metal Materials and Their Compounds)

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12 pages, 5063 KiB

Open AccessArticle

Synthesis, Characterization and Antimicrobial Studies of Ti-40Nb-10Ag Implant Biomaterials

by Bin Zhu, Yuqin Zhang, Yongcheng Chen, Ping Yuan, Wentong Wang, Hao Duan and Zhihua Wang

Metals 2022, 12(8), 1391; https://doi.org/10.3390/met12081391 - 22 Aug 2022

Cited by 6 | Viewed by 1685

Abstract

Bacterial infection and stress shielding are important issues in orthopedic implants. In this study, Ag element was selected as an antibacterial agent to develop an antibacterial Ti-40Nb-10Ag alloy by spark plasma sintering (SPS). The microstructure, phase constitution, mechanical properties, microhardness, and antibacterial properties [...] Read more.

Bacterial infection and stress shielding are important issues in orthopedic implants. In this study, Ag element was selected as an antibacterial agent to develop an antibacterial Ti-40Nb-10Ag alloy by spark plasma sintering (SPS). The microstructure, phase constitution, mechanical properties, microhardness, and antibacterial properties of the Ti-40Nb-10Ag sintered alloys with different sintering temperatures were systematically studied by X-ray diffraction (XRD), scanning electron microscope (SEM), microhardness tests, compressive tests, and antibacterial tests. The Ti-40Nb-10Ag alloys were mainly composed of α-Ti, β-Ti, and Ti2Ag intermetallic phases. This study shows that the change in sintering temperature affects the microstructure of the alloy, which results in changes in its microhardness, compressive strength, elastic modulus, and antibacterial properties. At the sintering temperature of 975 °C, good metallurgical bonding was developed on the surface of the alloy, which led to excellent microhardness, compressive strength, elastic modulus, and antibacterial ability with an antibacterial rate of 95.6%. In conclusion, the Ti-40Nb-10Ag alloy prepared by SPS at 975 °C is ideal and effective for orthopedic implant. Full article

(This article belongs to the Special Issue Preparation, Properties, Computational Simulations of Precious and Rare Metal Materials and Their Compounds)

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17 pages, 11343 KiB

Open AccessArticle

Comparison of Modified Johnson–Cook Model and Strain–Compensated Arrhenius Constitutive Model for 5CrNiMoV Steel during Compression around Austenitic Temperature

by Hengyong Bu, Qin Li, Shaohong Li and Mengnie Li

Metals 2022, 12(8), 1270; https://doi.org/10.3390/met12081270 - 28 Jul 2022

Cited by 3 | Viewed by 1888

Abstract

Isothermal compression behaviors of 5CrNiMoV steel were studied at temperatures of 870, 800, 750, and 700 °C, with strain rates of 0.001, 0.005, 0.01, 0.05, and 0.1 s⁻¹, the compression temperatures 870 and 800 °C are above Ac3, as well as [...] Read more.

Isothermal compression behaviors of 5CrNiMoV steel were studied at temperatures of 870, 800, 750, and 700 °C, with strain rates of 0.001, 0.005, 0.01, 0.05, and 0.1 s⁻¹, the compression temperatures 870 and 800 °C are above Ac3, as well as 750 and 700 °C below Ac3 temperature. The Modified Johnson–Cook (MJC) model and the Strain–Compensated Arrhenius (SCA) model were employed to demonstrate the relationship between the flow stress and the compression parameters. The correlation coefficient (R) and average absolute relative error (AARE) between the calculational and experimental flow stress were used to evaluate the accuracy of the two models. The results show that the effect of dynamic softening on flow stress is much more significant at higher temperatures and lower strain rates, while this effect is not obvious when the strain rate exceeds 0.005 s⁻¹ with the temperature below Ac3. The MJC model has a good accuracy close to the reference conditions (0.001 s⁻¹ and 700 °C), and it is suitable to predict the plastic behavior when the flow stress is lower than 200 Mpa. The unbiased AARE values were 6.82 and 5.71 for MJC model and SCA model, respectively, which implied the SCA model has a higher accuracy than the MJC model. The SCA model was believed to be capable of being used to illustrate the thermomechanical behavior of 5CrNiMoV tool steel in a wide range of plastic deformation conditions. Full article

(This article belongs to the Special Issue Preparation, Properties, Computational Simulations of Precious and Rare Metal Materials and Their Compounds)

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19 pages, 4839 KiB

Open AccessArticle

Anisotropic Elastic and Thermal Properties of M₂InX (M = Ti, Zr and X = C, N) Phases: A First-Principles Calculation

by Bo Li, Yonghua Duan, Mingjun Peng, Li Shen and Huarong Qi

Metals 2022, 12(7), 1111; https://doi.org/10.3390/met12071111 - 28 Jun 2022

Cited by 35 | Viewed by 2240

Abstract

First-principles calculations were used to estimate the anisotropic elastic and thermal properties of Ti₂lnX (X = C, N) and Zr₂lnX (X = C, N) M₂AX phases. The crystals’ elastic properties were computed using the Voigt-Reuss-Hill approximation. Firstly, [...] Read more.

First-principles calculations were used to estimate the anisotropic elastic and thermal properties of Ti₂lnX (X = C, N) and Zr₂lnX (X = C, N) M₂AX phases. The crystals’ elastic properties were computed using the Voigt-Reuss-Hill approximation. Firstly, the material’s elastic anisotropy was explored, and its mechanical stability was assessed. According to the findings, Ti₂lnC, Ti₂lnN, Zr₂lnC, and Zr₂lnN are all brittle materials. Secondly, the elasticity of Ti₂lnX (X = C, N) and Zr₂lnX (X = C, N) M₂AX phase are anisotropic, and the elasticity of Ti₂lnX (X = C, N) and Zr₂lnX (X = C, N) systems are different; the order of anisotropy is Ti₂lnN > Ti₂lnC, Zr₂lnN > Zr₂lnC. Finally, the elastic constants and moduli were used to determine the Debye temperature and sound velocity. Ti₂lnC has the maximum Debye temperature and sound velocity, and Zr₂lnN had the lowest Debye temperature and sound velocity. At the same time, Ti₂lnC had the highest thermal conductivity. Full article

(This article belongs to the Special Issue Preparation, Properties, Computational Simulations of Precious and Rare Metal Materials and Their Compounds)

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14 pages, 6816 KiB

Open AccessArticle

First-Principles Study on the Elastic Mechanical Properties and Anisotropies of Gold–Copper Intermetallic Compounds

by Jian Wang, Hongbo Qin, Junfu Chen, Daoguo Yang and Guoqi Zhang

Metals 2022, 12(6), 959; https://doi.org/10.3390/met12060959 - 2 Jun 2022

Cited by 11 | Viewed by 2607

Abstract

In this study, first-principles calculations were utilized to investigate the lattice constants, elastic constants, and mechanical properties of gold–copper (Au–Cu) intermetallic compounds (IMCs), including AuCu₃, AuCu, and Au₃Cu. We also verified the direction dependence of the Young’s modulus, shear [...] Read more.

In this study, first-principles calculations were utilized to investigate the lattice constants, elastic constants, and mechanical properties of gold–copper (Au–Cu) intermetallic compounds (IMCs), including AuCu₃, AuCu, and Au₃Cu. We also verified the direction dependence of the Young’s modulus, shear modulus, and Poisson’s ratio of the compounds. The calculated lattice parameters agreed with the experimental data, and the single-crystal elastic constants, elastic modulus E, shear modulus G, bulk modulus B, and Poisson’s ratio ν were calculated. For the Young’s and shear moduli, AuCu₃ showed the highest anisotropy, followed by AuCu and Au₃Cu. The Poisson’s ratios of AuCu₃ and Au₃Cu crystals were isotropic on (100) and (111) crystal planes and anisotropic on the (110) crystal plane. However, the Poisson’s ratio of the AuCu crystal was anisotropic on (100) and (111) crystal planes and isotropic on the (110) crystal plane. Full article

(This article belongs to the Special Issue Preparation, Properties, Computational Simulations of Precious and Rare Metal Materials and Their Compounds)

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