Alloying Effects On Mechanical Properties Of Ni₃Al:First-principles Study

In this paper,the first-principles method based on density functional theory is used to systematically study the site preference of alloy elements in Ni₃Al system and the influence of alloying elements on the tensile and shear deformation of Ni₃Al system.These alloys are Cr,Mo,W alloy elements in the same main group and Ta,W,Re alloy elements in the same period and metal elements Ru in platinum group.The site preference of alloying elements shows that both single alloying elements and co-alloying elements can be doped into Ni₃Al system stably.The stability of Ni₃Al system doped with co-alloying elements is lower than that of with single alloying element except for Ta.Cr,Mo,W,Ta,and Re prefer the Al site when they are doped into the Ni₃Al system seperately,and prefer the Al-Al double lattice sites when doped co-alloying elements.Ru has no obvious site preference.Moreover,when doping with co-alloying elements,the site preference of the individual alloying elements in the co-alloying elements does not change.The calculation results show that the ideal tensile strength and critical strain in the[001]and[111]directions of the Ni₃Al system are reduced when a single alloy element is doped,but the ideal tensile strength in the[110]direction is increased.After doping with co-alloying elements,the ideal tensile strength in the[110]direction is further improved.The strengthening effect of co-alloying element doping is greater than that of any single elements in the formation of co-alloying,showing a common strengthening effect.The ideal tensile strengths in the[110]direction of pure Ni₃Al,ternary Ni₃Al(W),Ni₃Al(Ta)and quaternary Ni₃Al(W-Ta)systems are 8.22GPa,10.85GPa,10.33GPa and 12.13GPa,respectively.The shear deformation calculation results show that the single alloy element can significantly improve the ideal shear strength of Ni₃Al system in both[1 10](111)and[112](111)directions,and the degree of enhancement increases with period number of alloying elements increases.The strengthening effect of co-alloying element doping is greater than that of any single elements in co-alloying.There is also a phenomenon of the common strengthening the shear deformation resistance.The ideal shear strengths in the[112](111)direction of pure Ni₃Al,ternary Ni₃Al(W),Ni₃Al(Re)and quaternary Ni₃Al(W-Re)systems are 3.67GPa,5.66GPa,5.64GPa and 6.81GPa,respectively.Combining the overall differential charge density and PDOS,it can be concluded that there are covalent-like bonds between the co-alloy atoms and the nearest neighboring Ni atoms.The covalent-like bond helps to improve the deformation resistance of the Ni₃Al system and the covalent-like bond between the co-alloying atoms and their common nearest neighboring Ni atoms makes the co-alloying atoms combine with the surrounding20 Ni atoms to produce a common strengthening effect,which is the main physical mechanism for the co-alloying elements to strengthen together.