Precipitation in a Ni–Al–Mo Directionally Solidified Eutectic Composite

Abstract

The influence of ageing treatments on the hardness and microstructure of directionally solidified eutectic composite of a Ni-12.7 at%Al-21.6 at%Mo alloy has been investigated. On ageing at temperatures between 873 and 1373 K after quenching from 1533 K two kinds of precipitates are formed in the γ phase depending upon the ageing temperature and the ageing time. At ageing temperature below 1100 K, a fine coherent metastable phase of orthorhombic Ni₂Mo is formed. By ageing above 1100 K, Mo platelets precipitate in the γ matrix at the expense of the metastable Ni₂Mo. The hardness of the material changes appreciably by the ageing treatments.