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.