First-principles calculations on structural energetics of Cu-Ti binary system intermetallic compounds in Ag-Cu-Ti and Cu-Ni-Ti active filler metals

Structural, mechanical and thermodynamic properties, as well as the electronic structures of Cu-Ti binary system intermetallic compounds in Ag-Cu-Ti and Cu-Ni-Ti active filler metals were calculated systematically using a first-principles density functional theory (DFT). The calculated formation enthalpy index that all the Cu-Ti intermetallic compounds are thermodynamic stable from degradation to pure metals and the relationship between Cu content (x) and formation enthalpy (y) for tetragonal structure meets the function y=0.572+(−1.005/(0.048*sqrt(3.142/2)))*exp(−0.5*((x−47.167)/13.533)^2). The mechanical properties, including bulk modulus B, shear modulus G, Young's modulus E and Poisson's ratio v, and elastic anisotropy were derived from the elastic data Cij. For the tetragonal Cu-Ti intermetallic compounds, the shear modulus G and Young's modulus E are negatively related to the formation enthalpy, while for the orthorhombic Cu-Ti intermetallic compounds, G and E are positively related to the formation enthalpy. Moreover, the elastic anisotropy increases in the following order: Cu4Ti