Effect of Ta substitution method on the mechanical properties of Ni3(Si,Ti) intermetallic alloy

In this study, Ta was added to an L12-type Ni3(Si,Ti) alloy at different levels and into different substitution sites, substituting for either Ni, Ti or Si. The solubility limits of Ta in the L12 phase were 1.9 at%, 5.7 at% and 1.0 at% when Ta substituted for Ni, Ti and Si, respectively. The lattice parameters in the L12 phase region increased in the order of the Ta(Ni)>Ta(Si)>Ta(Ti) quaternary alloys, in which Ta substituted for Ni, Si and Ti, respectively. The room-temperature hardness in the L12 phase region increased linearly with increasing Ta content, and the increment rate increased in the order of the Ta(Ni)>Ta(Si)>Ta(Ti) quaternary alloys. Similarly, the room-temperature 0.2% proof stress as well as the tensile strength in the L12 phase region increased linearly with increasing Ta content, and the increment rate increased in the order of the Ta(Ni)>Ta(Si)>Ta(Ti) quaternary alloys. High tensile elongation was observed at room temperature when the microstructures remain in the L12 single phase. At high temperatures, a positive temperature dependence of the hardness as well as the flow strength was observed in the quaternary alloys. It was also shown that the wear resistance of the quaternary Ta(Ti) alloys was improved and attributed to plastically induced hardening of the worn surfaces combined with the positive temperature dependence of the flow strength. The strengthening and hardening resulting from Ta addition was suggested to be due to the hardening of the solid solution arising from the misfits in the atomic radius between Ta and the constituent atoms Ni, Ti or Si.