Coefficients of thermal expansion of (Ni 0·5 Al 0·5 ) (1–x) Hf x alloys ( x =0...0·2)

Abstract

The coefficients of thermal expansion (CTEs) of Ni–Al–Hf alloys have been investigated due to their potential as corrosion resistant coatings in aggressive environments at high temperature. The CTEs of (Ni_0·5Al_0·5)_(1–x)Hf_x alloys (x=0...0·2) were measured between 473 and 1073 K (200–800°C) and range between 8 and 15×10^–6 K^–1 depending on temperature and alloy composition. The temperature dependence of the CTE was found to be properly described by a simple expression: (19·982–0·24016X_Hf)[0·15182+1·8287×10^–3(T/K)–2·12378×10^–6(T/K)²+8·87011×10^–10(T/K)³]. It was shown that the CTE of (Ni_0·5Al_0·5)_(1–x)H_fx alloys varies linearly with the amount of Hf in the alloy which allows the control of the CTE. Within the (Ni_0·5Al_0·5)_(1–x)H_fx alloy composition range (x=0...0·2) it covers the CTE range of most of the austenitic and ferritic steels and the CTE of the coatings can be adjusted to those of the substrate to be protected without inducing additional strains at the coatings/substrate interface.