First-principles Study on Mechanical Properties and Melting Curve of HfxTa1-xC System
HfxTa1-xC is a very promising candidate for thermal protection materials above 2000 ℃ due to its excellent properties such as high melting point,high hardness,high strength,high electrical conductivity,and high thermal conductivity.However,the rules of its mechanical properties and melting temperature varying with the composition remain elusive.Firstly,the mechanism of the variation of mechanical properties of HfxTa1-xC system solid solutions with its components was systematically investigated from the microscopic point of view of covalent bond strength and valence electron concentration(VEC)based on the special quasirandom structures(SQS)method and first-principles calculations.It revealed that among the five components of solid solutions(i.e.,HfC,Hf0.75Ta0.25C,Hf0.5Ta0.5C,Hf0.25Ta0.75C and TaC),the H f0.25Ta0.75C solid solution possessed the largest elastic modulus and shear modulus.It was mainly attributed to two reasons:(1)the component possessing the strongest covalent bonding strength among the above ternary compounds;(2)the special bonding states between the p-orbital from C and the d-orbital from Hf or Ta strongly resisting the deformation and being completely filled near VEC=8.75(for Hf0.25Ta0.75C).Secondly,the melting curves of the HfxTa1-xC system solid solutions were calculated using the ab initio molecular dynamics(AIMD)-based molecular dynamics Z method.It showed that there existed indeed the phenomenon for anomalous increase in the melting temperature of HfxTa1-xC system solid solutions,and the highest melting temperature of 4270 K was predicted on Hf0.5Ta0.5C,which was mainly attributed to the synergistic effect of the conformational entropy and the strength of the covalent bond.The results provide a theoretical guidance for the experimental selection of the optimal components of high melting temperature and high mechanical properties for HfxTa1-xC system solid solutions in the thermal barrier coating applications,as well as a reference for the study of other transition metal carbides.
HfxTa1-xCfirst-principlemechanical propertymelting temperature
万方数据
