Effect of Heat Treatment on the Microstructure of Multiphase NiAl-based Alloy

The alloy Ni-Al26.6-Cr13.4-Co8.l-Ti4.3-W1.3-Mo0.9 (at. pct) was fabricated from superalloy K44 and Al element using vacuum induction and casting technique. Investigations to this alloy reveal that a new phase Cr3Ni2 possessing low melting point and poor ductility is formed, which is distributed as a network along NiAl matrix grain boundaries. Subsequent different solution and aging treatments are carried out and lead to microstructural changes to various extents. Rapid cooling after solution at 1250℃ for 20 h gives rise to macrocracks in the specimen while slow cooling after the same treatment results in the formation of spheric α-Cr solid solution and needle-like Ni3Al phase, which are embedded in NiAI matrix. It is comfirmed that aging treatments initiate lath-shaped Ni3Al phase and pearl-shaped a-Cr phase to precipitate from the NiAl matrix, which own orientation relationships with these precipitates.