Search

In order to investigate the effect of porosity on the comprehensive performance of bioactive coatings， a TiO2 coating was prepared on the surface of TA2 pure titanium using micro-arc oxidation.By varying the concentrations of Na2B4O7 and NaOH in the electrolyte， the effects of electrolyte composition on the phase composition， microstructure， hardness， thickness and hydrophilicity of the micro-arc oxidation coating were examined under constant current mode.Results showed that the coating phase was primarily rutile TiO2.The phase composition， morphology， thickness， hardness and wear resistance of the coating were significantly affected by the concentrations of sodium hydroxide and sodium tetraborate.Moderate addition of NaOH can enhance the thickness， porosity， hardness， wear resistance and corrosion resistance of the coating.However， when the concentration of sodium hydroxide was too high， porosity decreased and coating performance was reduced.When the electrolyte formula was 0.15 mol/L NaOH and 0.10 mol/L Na2B4O7， a porous coating with a "trabecular bone-like" structure was prepared， exhibiting high porosity and good comprehensive performance.

For obtaining a thick ceramic coating with good film-forming and wear resistance, a new type of composite electrolyte was composed of sodium phosphate and sodium hexametaphosphate as the basic electrolytes, while sodium tungstate and sodium tetraborate were added as additives. In this composite electrolyte system, micro-arc oxidation treatment was performed on 1060 aluminum alloy. Using the coating thickness and surface porosity as optimization indicators, the electrolyte formula was optimized using the L9(34) orthogonal test. Meanwhile, the microstructure, surface porosity, phase composition, thickness, microhardness and wear resistance of ceramic coatings prepared under this electrolyte formula were studied systematically. Results showed that the ceramic coating prepared with a formula of Na3PO4 concentration of 32.0 g/L, Na2B4O7 concentration of 16.0 g/L, Na2WO4 concentration of 4.5 g/L and(NaPO3)6 concentration of 30.0 g/L had the structure with uniform micropores and dense film layer, the thickness of 22.8 μm, the porosity of 3.86%, and the microhardness of 475 HV. Furthermore, the wear resistance of the coating was significantly improved compared to the substrate, and the ceramic coating were mainly composed of γ-Al2O3 and a small amount of α-Al2O3 composition.

In this work, first‐principles calculations were used to study the structural, elastic and thermodynamic properties of Mg17Al12 and M‐doped Mg17Al12 (Mg16Al12M, M = Ga, In, Ge, Sn, Pb) compounds. The calculated results show that Mg16Al12M compounds have negative defect formation energies, the calculated phonon dispersions have no imaginary frequencies, and their single‐crystal elastic constants satisfy the mechanical stability criterion. Thus, Mg16Al12M compounds are thermodynamically, dynamically and mechanically stable. The calculated GH/BH, Poisson's ratio v and Cauchy pressure values indicate that Mg17Al12 and Mg16Al12M are ductile, the ductility of the doped system is greater than that of Mg17Al12. Mg17Al12 and Mg16Al12M have elastic anisotropy, and the order of anisotropy is Mg16Al12Sn > Mg16Al12Ga > Mg16Al12In > Mg17Al12 > Mg16Al12Ge > Mg16Al12Pb. Finally, the minimum thermal conductivities based on Clarke's and Cahill's models were discussed, and the results show the heat transfer rates of Mg17Al12 and Mg16Al12M along the [111] direction are faster than those along other directions. [ABSTRACT FROM AUTHOR]

In this paper, based on density functional theory, the structural stability and mechanical properties of AuIn2 doped with RE (RE = Y, Sc) were investigated. The bulk modulus, shear modulus, Young's modulus and Poisson's ratio of the materials were calculated by Viogt−Reuss−Hill approximation. The calculation results show that Sc−SAu (trace of Au substituted by Sc in AuIn2), Y−SAu and Y−SIn have stable structure, and Y−SAu has obvious effect on the toughness indexes of AuIn2 alloy. Furthermore, based on Clarke and Cahill modes, the lattice thermal conductivity of the intermetallic compound was calculated and shows the same tendency with the Debye temperature and fast heat transfer rate in the direction of [110]. [ABSTRACT FROM AUTHOR]

The electronic, elastic, and thermal properties of TM5SiB2 (TM = V, Nb, and Ta) MAB phases are calculated herein using first-principles calculations. The obtained electronic structures show that there are p-d hybridizations between B, Si, and TM atoms, and TM-B and TM-Si bonds are formed by the electrons transfer between TM and B, TM and Si. Elastic Modulus and elastic Anisotropy Index, three-dimensional surface construction, and two-dimensional projection are used to discuss the elastic anisotropy, and the results show that these TM5SiB2 MAB phases are anisotropic in elastic modulus with the order of V5SiB2 > Nb5SiB2 > Ta5SiB2. Besides, the Debye temperature and sound velocity of these TM5SiB2 are also analyzed. The thermal conductivities are obtained, and the thermal conductivity is also anisotropic and in the same order as elastic modulus. [ABSTRACT FROM AUTHOR]

In our work, to figure out the effects of V and Si vacancies on formation energies, elastic properties, phonon dispersions, electronic structures, and thermodynamic properties of VSi2, we used first-principles calculations. VSi2 with V and Si vacancies are dynamically and thermodynamically stable from the calculated formation energies and phonon dispersions. Moreover, VSi2 with V and Si vacancies are mechanically stable certified by single-crystal elastic constants. The presence of different atomic vacancies can weaken the bond strength of V–Si and Si–Si bonds, and eventually leads to the decreasing phase stability and elastic modulus, but can increase elastic anisotropy and ductileness. Finally, thermodynamic properties, including Debye temperature, sound velocities, and directional sound velocities, of perfect VSi2 and VSi2 with different vacancies are calculated. Highlights Based on the calculated vacancy formation energies and phonon dispersions, the perfect VSi2 and VSi2 with different vacancies are thermodynamically and dynamically stable. The vacancies can reduce the thermodynamical stability of VSi2, VSi2 with V vacancies are more stable than those with Si vacancies, and among VSi2 with vacancies, VSi2 with V-Va1 is the most stable. The perfect VSi2 and VSi2 with different vacancies are brittle, and the atomic vacancies can improve the ductility of VSi2 slightly, but can weaken the elastic modulus. The order of elastic anisotropy is Si-va3 > Si-va1 > Si-va2 > V-va2 > V-va1 > perfect VSi2. The Si–Si and V–Si bonds are broken after Si or V atoms removed, resulting in the decreasing bond strength in VSi2 with vacancies, and eventually leading to the lower phase stability and elastic moduli of VSi2 with vacancies compared to the perfect VSi2. The calculated sound velocities also show anisotropy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the present study, we calculated the effects of boron content on the elastic properties, fracture toughness, ideal tensile strength ([0001] and [11 2 ¯ 1] directions) and thermal conductivities of the stable hexagonal tungsten borides (hP12-WB2, hP16-W2B5, hP16-WB3 and hP10-WB4) by the first-principles calculations. The results showed that the hardness of the four tungsten borides is ranked in the order hP16-WB3 > hP10-WB4 > hP16-W2B5 > hP12-WB2, and hP16-WB3 is the hardest with the hardness of 36.9 Gpa and can be considered as a potentially superhard material. The fracture toughness of these tungsten borides decreases as the boron content increases. Moreover, the [0001]-direction ideal tensile strength and the thermal conductivities increase with the increase in boron content. The [0001]-direction ideal tensile strength is in the sequence of hP10-WB4 > hP16-WB3 > hP16-W2B5 > hP12-WB2. Finally, the thermal conductivities of these borides are anisotropic and in the order of hP10-WB4 > hP16-WB3 > hP16-W2B5 > hP12-WB2. [ABSTRACT FROM AUTHOR]

In our work, to figure out the effects of V and Si vacancies on formation energies, elastic properties, phonon dispersions, electronic structures, and thermodynamic properties of VSi2, we used first-principles calculations. VSi2 with V and Si vacancies are dynamically and thermodynamically stable from the calculated formation energies and phonon dispersions. Moreover, VSi2 with V and Si vacancies are mechanically stable certified by single-crystal elastic constants. The presence of different atomic vacancies can weaken the bond strength of V–Si and Si–Si bonds, and eventually leads to the decreasing phase stability and elastic modulus, but can increase elastic anisotropy and ductileness. Finally, thermodynamic properties, including Debye temperature, sound velocities, and directional sound velocities, of perfect VSi2 and VSi2 with different vacancies are calculated. Highlights Based on the calculated vacancy formation energies and phonon dispersions, the perfect VSi2 and VSi2 with different vacancies are thermodynamically and dynamically stable. The vacancies can reduce the thermodynamical stability of VSi2, VSi2 with V vacancies are more stable than those with Si vacancies, and among VSi2 with vacancies, VSi2 with V-Va1 is the most stable. The perfect VSi2 and VSi2 with different vacancies are brittle, and the atomic vacancies can improve the ductility of VSi2 slightly, but can weaken the elastic modulus. The order of elastic anisotropy is Si-va3 > Si-va1 > Si-va2 > V-va2 > V-va1 > perfect VSi2. The Si–Si and V–Si bonds are broken after Si or V atoms removed, resulting in the decreasing bond strength in VSi2 with vacancies, and eventually leading to the lower phase stability and elastic moduli of VSi2 with vacancies compared to the perfect VSi2. The calculated sound velocities also show anisotropy. [ABSTRACT FROM AUTHOR]