First Principles Study On Mechanical And Thermodynamic Properties Of Metal Carbides

Metal carbides have high melting points,high hardness,wear resistance,corrosion resistance,good toughness and low thermal expansion coefficients.They are widely used in aerospace,nuclear industry and other fields.It is essential to deeply understand the nature of the excellent mechanical and thermodynamic properties of these materials,confirm their temperature dependence,and rationally apply these materials in extreme environments,as well as design new materials to further improve their mechanical strength and stability.At present,research on metal carbides focuses more on their crystal structure,phase stability and electronic properties,while their mechanical and thermodynamic properties need further study.Moreover,the existing prediction models of elastic modulus and thermal expansion coefficient,which are crucial physical quantities in material design,cannot be effectively applied to metal carbides.Therefore,this paper systematically studies the mechanical and thermodynamic properties of binary metal carbides using first-principles based on density functional theory and provides prediction models for the Young’s modulus and thermal expansion coefficient of these materials.The main contents of the paper are as follows:Firstly,a lattice structure with the lowest energy in the binary metal carbides corresponding to each metal in the Materials Projects database was constructed.Structural optimization was carried out using first principles to obtain the optimized lattice parameters.The thermal stability of the constructed structure was analyzed by calculating the enthalpy of formation,and the elastic constants of the system with thermal stability were calculated using the difference method,Based on the generalized stability criterion,the mechanical stability of various system carbides was determined,and metal carbides that meet both thermal and mechanical stability were obtained.Secondly,the mechanical properties of the constructed binary carbides were studied,and the variation rules and influencing factors of mechanical properties such as bulk modulus,shear modulus,Young’s modulus,Poisson’s ratio,Pugh’s ratio,hardness and elastic anisotropy of the materials were systematically studied.A simple and easy-to-calculate model suitable for predicting the Young’s modulus of metal carbides was proposed,which includes not only the volume and electronegativity,which affect the Young’s modulus,but also the influence of valence electrons.The determination coefficient of the prediction model is 0.90.Based on this model,the Young’s modulus of metal carbides can be quickly and accurately predicted.Then,taking TiC with NaCl structure as a research sample,the thermal expansion coefficients under different parameter settings were obtained by changing different calculation parameter settings.The influence of different parameters on the thermal expansion coefficient was analyzed,which has certain guiding significance for the calculation of the thermal expansion coefficient.By comparing with experimental data,it is determined that the optimal parameter setting for calculating the thermal expansion coefficient is the combination of LDA functional and primitive cell.Finally,the thermodynamic properties of metal carbides,such as sound velocity,Debye temperature,heat capacity,adiabatic bulk modulus,and coefficient of thermal expansion,were studied to fill in the lack of reference data for related properties.Using atomic radius,electronegativity,and Debye temperature as parameters,a model was established to quickly and accurately predict the thermal expansion coefficient of metal carbides,with a determination coefficient of 0.90.