Abstract
The phase NiAl with its wide homogeneity range, and especially when of high Al content, is a reliable alumina scale former and exhibits remarkable oxidation resistance at high temperatures. By contrast, the line phase NbAl3 oxidises with formation of mixed layers of Al2O3 and fast growing oxides. However, the mechanical strength of NiAl is not sufficient for application at high temperatures, but the strength is enhanced in multiphase alloys in the systems Ni–Al–Cr and Nb–Ni–Al. Increasing the Cr content of two phase NiAl–Cr alloys reduces the oxidation resistance, but for three phase NbAl3–NbNiAl–NiAl alloys the oxidation resistance is comparable to that of NiAl, since the Al content of the phases NiAl and NbNiAl is high in the phase equilibrium.
MST/1570
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