Precipitation in the Ni•Cu-base alloy monel K-500

Abstract

The precipitation of the intermetallic γ' phase and of carbide phases in the Ni•Cu-base aluminium- and titanium-bearing age-hardenable alloy Monel K-500 has been investigated, using transmission electron microscopy. It was found that the γ ' particles nucleate homogeneously and remain spherical in shape and coherent with the matrix even after prolonged aging. The coarsening kinetics of these precipitates were examined and a linear dependence of the average precipitate radius on the cube root of the aging time was observed. The principal carbide phase in this alloy was identified as a titanium-rich MC-type phase, coarse particles of which are distributed in a non-uniform manner within the grains and also at the grain boundaries. In addition, a grain boundary carbide phase, isostructural with Cr₂₃C₆, was found to form in this chromium-free alloy on aging.