Phase equilibria between the B2, L12, and fcc phases in the Ir–Ni–Al system

The isotherms of the Ir–Ni–Al in the composition range up to 50 at% Al are presented at 1573 K. The phase constitution and microstructure of the Ir–Ni–Al alloys were examined using X-ray diffractometry (XRD), scanning electron microscopy (SEM) with an electron probe microanalyzer (EPMA), and transmission electron microscopy (TEM) after heat treatment at 1573 K for 168 h. The B2-NiAl and B2-IrAl phases connected with each other at 1573 K. The highest solubility limit of Ir into Ni₃Al was about 3.5 at% in the tested alloys. Then, a wide fcc + B2 and a narrow fcc + L1₂ and B2 + L1₂ two-phase region appeared in the isothermal section. In part of the B2 phase, a martensitic transformation from the B2 to the L1₀ phase was observed.