Manganese enriched diffusion layers on NiAl alloy

Abstract

Materials based on Ni–Al intermetallics are prospective high temperature materials. Properties of these intermetallics can often be improved by surface diffusion layers enriched by various metals. In this contribution results of a study are presented about microstructure and composition of Mn enriched diffusion layers on a NiAl alloy.

A pure Mn plate was annealed at 900°C for 4 h in contact with a prism of the NiAl phase. The ordered B2-NiAl (β′) phase can absorb only a few per cent of manganese without structural changes. When absorbing more Mn, the ordrerd B2-NiAl phase transforms into the disordered bcc β′ NiMnAl phase forming the first structurally different (narrow) layer on NiAl. Its Mn content increases from 25 wt-% (in contact with B2-NiAl phase) up to 35 wt-% across this homogeneous layer. Higher average Mn content in the next layer manifests in precipitation of β-Mn particles (containing several per cent of Ni and Al) from the β″ matrix. Owing to diffusion of Ni and Al into the original Mn plate the β″ NiMnAl precipitates are formed in the Mn matrix containing several per cent of Ni and Al (when studying microstructure and composition at room temperature after annealing).