First-principles Study On The Stability Of Multicomponent B1-type Carbide

Multi-component B1 type carbide are important to steel materials due to their excellent thermal stability and remarkable precipitation strengthening effect of nano-scale high-density precipitation,which are of very significant for improving the mechanical performances of steel materials.In addition,it is also very vital to the production,application and safety of steel materials to clarify the physical mechanism of hydrogen embrittlement in high-strength steel.This paper is supported through the National Natural Science Foundation of China,"Based on the principle of first-principles,the organization and performance control of multi-phase steel with high strength andhigh local forming properties(No.51774083)".Based on the first-principles calculation method of density functional theory,the influence of multi-component B1 type carbide formed in Mo,W,Cr,Zr doped Ti-V,Ti-Nb steel on the structural stability and the mechanism of H atom trapping by VC were studied.The main contents and conclusions of this paper are shown as follows:(1)Linear interpolation is used for Bl-type ternary carbide(Ti1-xMx)C(M=V,Cr,Zr,Nb,Mo,W),quaternary carbide(TixV0.7s-xM0.25)C and(TixNb0.75-xM0.25)C lattice constant is predicted,which provides theoretical guidance for the preparation of new multivariate composite carbide.The results show that(Ti1-xMx)C(M?Cr,Mo and W)should consider the influence of vacancy when using linear interpolation formula;The relationship between the values of y in MoCy and WCy and x in(Ti1-xMx)Cz shows that the effect of vacancies on the lattice constant of(Ti1-xMx)C gradually decreases with x increases from 0.1 to 0.5;The interaction of different alloying elements results in(Ti1-xMx)Cz using the interpolation method in the MoCy y value range from 0.61 to 0.74,and the WCy y value range is about 0.6.(2)The structural stability of type B1(TixV0.75-xM0.25)C(M=Cr;Zr,Mo and W)and(TixNb0.75-xM0.25)C(M=Cr,Zr,Mo and W)is investigated.The results show that(TixV0.75-xM0.25)C and(TixNb0.75-xM0.25)C system formation energy decreases as x increases,(Ti0.62sV0.125M0.25)C and(Ti0.625Nb0.125M0.25)C system structure exhibit excellent stability,and the stability from strong to weak is Nb>Zr>W>Mo>Cr,which provides a reference for new multi-component composite carbide.(3)The interaction between H and VC is investigated.The results show that the of VC tetrahedral site is unstable compared with VC when H is captured;Hydrogen atoms tend to occupy V4C3 vacancy,which can serve as irreversible hydrogen trap;After V4C3 captures H2,hydrogen exists in vacancy as an atomic state;VCx with different vacancy concentrations can be formed;When CVac=12.5%,V4C3 with 2×2×2 unit cell can capture more than 12 hydrogen atoms,.which indicates the direction of hydrogen trap design for high strength steel carbide.