Alloy design for Al addition on microstructure and mechanical properties of Ni3(Si,Ti) alloy

The effect of Al addition on the microstructure and tensile properties of Ni₃(Si,Ti) alloys with an L1₂ ordered structure, which were fabricated through thermomechanical processing from arc-melted ingots, was investigated. Al was added to a Ni₃(Si,Ti) alloy by using two methods such that Al substituted for (1) only Ti and (2) both Ni and Ti along a Ni₃(Si,Ti)-Ni₃Al pseudo-binary line. In the case of the alloys prepared by the former method, the addition of more than 4 at.% Al resulted in a two-phase microstructure consisting of disordered fcc Ni solid solution dispersions in the L1₂ matrix, while in the case of the alloys prepared by the latter method, the addition of 4 at.% Al retained the L1₂ single-phase microstructure. In the case of the 4 at.% Al-added alloys, the room-temperature tensile properties were similar and independent of the alloying methods, whereas the high-temperature yield stress was higher in the alloys prepared by the latter method than in the case of the alloys prepared by the former method. These results suggest that a single-phase microstructure consisting of an entire L1₂ structure is favorable for obtaining high-temperature tensile properties.