Solid state morphological instability of Ni 4Mo precipitates

Abstract

The morphology of ordered Ni 4Mo precipitates in an off-stoichiometric Ni-Ni 4Mo alloy is documented at relatively high aging temperatures (low supersaturation) and compared to the precipitate morphology at low to intermediate aging temperature (large supersaturation). It is found that the precipitate morphology is a function of the aging temperature. In particular, at low aging temperatures the precipitates develop into ellipsoids with a square cross-section. At high temperatures, the precipitates appear to be subject to morphological instabilities normally associated with liquid-to-solid transformations. Consequently, the observed precipitates tend to form solid-state dendritic protrusions at the high aging temperatures.