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

The most recently developed high temperature materials are known as in-situ composites or directionally solidified eutectics. Since the composites are formed during solidification, they have excellent morphological stabilities up to near their melting temperatures. The Ni-Al-Mo system has received the greatest attention for recent several years(1)~(3) since the alloy is expected to form a structure consisting of ductile α-Mo fibers aligned in aductile γ+γ' matrix†. However variations in microstructures and the resultant strength by thermal treatments have not been investigated in earlier papers(1)~(3). In a separate paper(4) the present authors have reported the detailed microstructural analysis of as-grown composite and the microstructural and strength variations of the composite due to quenching from high annealing temperatures. The present paper describes the microstructural changes occurring during ageing of a Ni-12.7at%Al-21.6at%Mo alloy composite after quenching from 1533K studied by transmission electron microscopy