Effect of alloying elements (Ni, Co, Cr, and Sn) on the mechanical properties of W–Cu alloy system predicted from first principles

In order to explore the reasons for the influence of alloying element X (X = Ni, Co, Cr, and Sn) on the strength, hardness and toughness of W–Cu alloy, this paper calculated the elastic constants and electronic structures of W–Cu alloy and W–X–Cu alloy based on first principles, and quantitatively evaluated the influence of alloying element X on the strength, hardness and toughness of W–Cu alloy from the atomic level. The results show that the W–Ni–Cu alloy system has the best strength and hardness when the doped content of Ni is 3.125%, and the alloy system has the best stiffness when the doped content of Cr is 12.5%. The electronic structure analysis shows that the charge density of Ni-3d, Co-3d, Cr-3d and Sn-5p orbitals increases with the increase of alloyed element doping ratio. Alloyed atom doping generates new chemical bonds in the system, and weakens the hybridization between Cu 3d and W 5d orbitals, thus affecting the bonding strength of W–Cu bonds. W–X bond is always a strong covalent bond, which can make up for the weakening of W–Cu bond to a certain extent. W–Cu bond and W–X bond jointly determine the strength and hardness of the system. Alloying atom X also changes the electron distribution on the 3d and 4 s orbitals of Cu atom, resulting in changes in the charge density between neighboring Cu atoms, which affects the toughness of the material system.