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 degrees C to 1200 degrees C. A phase transformation occurred at temperatures between 1000 degrees C-1050 degrees C, which was confirmed as a four-phase reaction, gamma'-Ni3Al+alpha-Cr ->gamma-Ni+beta NiAl. The beta-NiAl phase was observed to undergo a martensite transformation in the specimens that were quenched from temperatures above 1000 degrees 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. (C) 2011 Elsevier B.V. All rights reserved.
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