Strengthening of oxidation-resistant Fe-Cr-Al-Y alloys by directional solidification of eutectic compositions

Abstract

Two eutectic alloys having solid-solution Fe-Cr-Al-Y matrixes reinforced by fibres of (Fe, Cr)₇C₃ have been identified and aligned by directional solidification. Alloy A (60·2Fe-33·2Cr-3·2Al-2·6C-0·8Y), which has a ferritic matrix and has good cyclic oxidation resistance to 1373 K, has better creep properties than existing ferritic alloys. Its stress-rupture properties are strongly influenced by the dimensions of the fibres which are subject to a phase transformation; at 973 K the optimum creep properties are obtained with a mean fibre radius of 2·5 μm. Alloy B (60·2 Fe-18·2Cr-15·0 Ni-3·2Al-0·8Y-2·6C), which has an austenitic matrix, has poorer oxidation resistance but preliminary tests show the stress-rupture properties to be superior to those of current iron-base materials, approaching the behaviour of nickel-base superalloys such as Nimonic 115.