Xinyu Wang

Bio: Xinyu Wang is an academic researcher from Kunming University of Science and Technology. The author has contributed to research in topics: Materials science & Boriding. The author has an hindex of 4, co-authored 8 publications receiving 40 citations.

Insight into structural, electronic, elastic and thermal properties of A15-type Nb3X (X = Si, Ge, Sn and Pb) compounds

Abstract: Niobium-based compounds with the A15 structure have been widely applied in fusion engineering test reactor and superconducting materials. Hence, for a better understanding of the physical properties of A15-type Nb3X (X = Si, Ge, Sn and Pb) compounds, their structural, electronic, elastic and thermodynamic properties were investigated using the first-principles calculations. The calculated formation enthalpies indicated that these Nb3X compounds are energetically favorable and the sequence of thermodynamic stability is Nb3Si > Nb3Ge > Nb3Sn > Nb3Pb. Meanwhile, the phonon dispersions verified that these Nb3X compounds are dynamically stable. The electronic properties, such as the density of state, band structure, electron density difference and Mulliken population, suggested that these compounds are metallic, and Nb-Nb and Nb-X chemical bonds are ionic-covalent mixed bonds. The single-crystal and polycrystalline elastic properties were calculated. Moreover, the elastic anisotropy was discussed by elastic anisotropic indexes, three-dimensional surface construction and planar projections of elastic modulus, and the sequence of elastic anisotropy is Nb3Si > Nb3Ge > Nb3Sn > Nb3Pb. Finally, thermal properties such as Debye temperatures and sound velocities were analyzed based on elastic moduli.

Explorations of electronic, elastic and thermal properties of tetragonal TM4N3 (TM=V, Nb and Ta) nitrides

Abstract: In this work, we performed the first-principles calculations to reveal the electronic, elastic and thermal properties of the tetragonal TM4N3 (TM V, Nb, Ta) nitrides. The obtained electronic structures indicated that there is the p-d hybridization between N and TM atoms, and the electrons transfer from TM to N atoms to form TM N bonds. The polycrystalline elastic modulus was obtained from the single-crystal elastic constant. Based on the elastic constants and moduli, the elastic anisotropy was discussed by elastic anisotropy indexes and three-dimensional (3D) surface construction and its projection. Besides, Debye temperature, sound velocity and minimum thermal conductivity were also analyzed. The results showed that these nitrides are mechanically stable and ductile. Meanwhile, the elastic and thermal properties of the tetragonal TM4N3 (TM V, Nb, Ta) nitrides are anisotropic, and the order of anisotropy in elastic modulus and minimum thermal conductivity for TM4N3 (TM V, Nb and Ta) nitrides is V4N3 > Nb4N3 > Ta4N3.

The vacancy defects and oxygen atoms occupation effects on mechanical and electronic properties of Mo5Si3 silicides

Abstract: Improving brittle behavior and mechanical properties is still a big challenge for high-temperature structural materials. By means of first-principles calculations, in this paper, we systematically investigate the effect of vacancy and oxygen occupation on the elastic properties and brittle-or-ductile behavior on Mo5Si3. Four vacancies (Si–Va1, Si–Va2, Mo–Va1, Mo–Va2) and oxygen occupation models (O–Mo1, O–Mo2, O–Si1, O–Si2) are selected for research. It is found that Mo–Va2 vacancy has the stronger structural stability in the ground state in comparison with other vacancies. Besides, the deformation resistance and hardness of the parent Mo5Si3 are weakened due to the introduction of different vacancy defects and oxygen occupation. The ratio of B/G indicates that oxygen atoms occupation and vacancy defects result in brittle-to-ductile transition for Mo5Si3. These vacancies and the oxygen atoms occupation change the localized hybridization between Mo–Si and Mo–Mo atoms. The weaker O–Mo bond is a contributing factor for the excellent ductile behavior in the O-Si2 model for Mo5Si3.

Effect of structural vacancies on lattice vibration, mechanical, electronic, and thermodynamic properties of Cr₅BSi₃

Abstract: In recent years, transition metal silicides have become the potential high temperature materials. The ternary silicide has attracted the attention of scientists and researchers. But their inherent brittle behaviors hinder their wide applications. In this work, we use the first-principles method to design four vacancy defects and discuss the effects of vacancy defects on the structural stability, mechanical properties, electronic and thermodynamic properties of hexagonal Cr 5 BSi 3 silicide. The data of lattice vibration and thermodynamic parameters indicate that the Cr 5 BSi 3 with different atomic vacancies can possess the structural stabilities. The different atomic vacancies change the mechanical properties and induce the Cr 5 BSi 3 to implement the brittle-to-ductile transition. The shear deformation resistance and volume deformation resistance of Cr 5 BSi 3 are weakened by different vacancy defects. But the brittleness behavior is remarkably improved. The structural stability and brittle-to-ductile transition of Cr 5 BSi 3 with different vacancies are explored by the electronic structures. Moreover, the thermal parameters indicate that the Cr 5 BSi 3 with vacancies exhibit different thermodynamic properties with temperature rising.

Growth kinetics of the FeB/Fe2B boride layer on the surface of 4Cr5MoSiV1 steel: experiments and modelling

Abstract: The boriding of 4Cr5MoSiV1 steel was performed in the temperature range of 860°C–980 °C to examine the influence of boriding conditions on the boride layers The experimental results show the formation of FeB and Fe2B layers with the predominant saw-tooth morphology The boride layer depth increases with increase the boriding temperature and time Thick and compact boride layers could be obtained at temperatures higher than 900 °C The growth kinetics of boride layers is characterized by a parabolic curve FeB and Fe2B exhibit a hardness of 1600HV01 and 1300HV01, respectively, which is 4 and 3 times that of the substrate A diffusion model, based on the boron concentration profiles of the surface layers and the parabolic growth law, was established to predict the growth kinetics of the boride layers including both the FeB and the Fe2B layer A satisfactory agreement between the model and experimental results was obtained The work thus provides an approach to investigate and to predict the boride layer growth of 4Cr5MoSiV1 steel in the boriding process