Phase stabilities in a NiCrAlYRe coating alloy

MCrAlY can serve as stand-alone overlay coatings or bond coats in thermal barrier coating systems, and its phase stabilities play a vital role in determining the performance of these coating systems. In the present paper, the phase evolution of a NiCrAlY model coating alloy containing Re was investigated by experimental observation and thermodynamic modeling in the temperature range from 800 °C to 1200 °C. A phase transformation occurred at temperatures between 1000 °C–1050 °C, which was confirmed as a four-phase reaction, γ′-Ni3Al + α-Cr → γ-Ni + β-NiAl. The β-NiAl phase was observed to undergo a martensite transformation in the specimens that were quenched from temperatures above 1000 °C, and this NiAl martensite could affect the microhardness of the NiCrAlY coating alloy significantly. TEM analysis illustrated that between the martensitic plates existed a twin boundary (macrotwin), and within the martensitic plates many nano striations (microtwins) were present.