Decomposition of Gamma-Phase Manganese Copper Alloys

Abstract

The decomposition of γ‐Mn–Cu alloys containing more than 60 at.% Mn to the mixed (α+γ) phase has been studied using x‐ray and neutron diffractometry and measurements of electrical resistance and Young's modulus of elasticity. There is strong evidence that manganese‐enriched clusters having the γ‐phase structure are produced prior to the precipitation of α‐Mn. When γ‐phase alloys were aged at 450°C for increasing periods of time, they remained single phase, but developed long‐range antiferromagnetic order associated with a tetragonal (c/a<1) lattice distortion, and with a corresponding rise of the Néel temperature to an asymptotic value of ∼470°K for all compositions. The effects of aging at other temperatures, and the behavior of furnace‐cooled alloys are discussed in terms of the pre‐precipitation of manganese‐rich clusters.