The Effect of Refractory Elements on Microstructure and Mechanical Properties of Ni3(Si,Ti) Intermetallic Alloys

Microstructure, mechanical properties and cold workability of quaternary Ni(3)(Si,Ti) intermetallic alloys with L1(2) structure, which were alloyed with two atomic percent of a refractory element X (X: I-If, Ta and W), were investigated. The Ta-added Ni(3)(Si,Ti) alloy showed an L1(2) single phase microstructure, while the microstructure of the Hf-added alloy was comprised of Ni(5)Hf and/or Ni(3)Hf intermetallic dispersions in the L1(2) matrix, and that of the W-added alloy consisted of fcc Ni solid solution phase within the L1(2) grain. In the homogenized condition, hardness increased in the order of the Hf-added, the Ta-added and the W-added alloys. The hardenings of the Hf-added and the Ta-added alloys were attributed to second-phase dispersion hardening and distinctive solid solution hardening, respectively. Among these alloys, only the W-added alloy was successfully cold-rolled to thin sheet with a thickness of 200 mu m. It was found that both room-temperature and high-temperature tensile strength of the W-added alloy sheet was enhanced compared with that of the unalloyed Ni3(Si,Ti) sheet. Also, high-temperature tensile ductility was significantly improved in the W-added alloy sheet, by suppressing the propensity of brittle intergranular fracture.