Theoretical Study On The Properties Of Carbide Disperson W Alloy Interfaces And Impurities Segregation

Tungsten and its alloys are consdiereded as the most promising candidate for the plasma-facing materials(PFMs)of future fusion reactors.Because the W exhibits the low-temperature embrittlement and radiation embrittlement,and therefore,researchers focus on the dispersion stengthen W materials by adding a second-phase carbide particles in recent years.The interfaces between carbide and W matrix play an enssential role in improvement of the overall performance of W-based materilas,i.e.,mechnanical properties and irradiation resistance.Furthermore,during the service and manufacture,the impurities such as H,He,N and O are easily segregated to interface,leading the decrease of the overall performance of materials.Therefore,In this work,first-principles calculations are performed to study the stability,adhesion strength,the electronic structure of typical interfaces,i.e.,W-ZrC interfaces,W-TiC interfaces,W-Ta interfaces,W-ZrO2 interfaces,and the behaviour of segregation and diffusion,which provides a scientific basis for understanding the properties of interfaces in carbied disperssion strengthen tungsten,impurities segregation and the improvement of the overall performance of W alloys.Firstly,accoding to the orientation relatinship and the lattice constant of W and ZrC,we investigate interface stability and the overall performance of twelve different bulk-like interfaces.The results denote that the C-terminal ZrC(111)/W(110)has the stongest adhesion strength and the stoichimetric ZrC(200)c/W(100)interface exhibits the best stability.The electronic structure analyses indicate that Charge transfer from interfacial W to C atoms across the interface,and the C-W bonds formed by the strong hybridization between C-2p and W-5d are covalent bonds.The segregation energies of impurities H and He are-1.00 eV and-2.03 eV,respectively.And H prefers to segregate to the interface.The diffusion energy barrier of H and He along the interface are much lower than those of across the interface,which denote that H and He prefer to segregate to interface and diffuse along the interface.Secondly,we systematively investigate the properties of coherent and semi-coherent W-TMC(TMC=Mo,Ta,Ti,Zr,Hf and V)interfaces and the interfaces doped with light elment impurities(H,He,Li,Be,B,C,N,O,S and P).After subtracting off the contribution of strain energy,the interface energy of coherent TMC(100)/W(100)interfaces are larger than those of semi-coherent TMC(100)/W(110)interfaces which denotes that the former interfaces are more stable.And the interface energy of MoC(100)/W(100)(-0.44 eV)is negative meaning diffusion occurring among interfacial W,C and Mo atoms.When ZrC(100)/W(100)and TiC(100)/W(100)interfaces doped with different impurities,the impurities prefer to segregate to the interface inducing the decrease of cohesion of interface system.Our results are helpful for understanding the mechanism of improving the mechanical proerties and radiatin resistance,and proposing guidelines for the interface design of W materials with advanced properties.Finally,we systematively investigate the properties of ZrO2(001)/W(001)interface.The sandwich W(001)/ZrO2(001)1ML/W(001)interface with the lowest interface energy is the most stable of the five interface structures.The strong O-W covalent bonds are formed by the hybridization between O-2p and W-5d.ZrO2(001)Zr/W(001)interface has the largest ideal work of separation,2.36 eV.As tensile tests,the fracture plane may be not the interface and firstly broken between O atoms.The ZrO2(001)Zr/W(001)interface has the largest values of the fracture energy(13.74 J/m2)and the maximum theretical strength(7.20 GPa),and those of the sandwich W(001)/ZrO2(001)2ML(001)interface are smallest.Our results are helpful for understanding the effect of the dispersed ZrO2 particles on interfacial adhesion as O atoms segregate to interface.