Effects of Combined Additions of Al, Be, and Ti on Precipitation Hardening of Fe-Ni Alloys

Abstract

Effects of combined additions of Al, Be, and Ti on age hardening characteristics and precipitated phases in Fe-4-7% Ni alloys were investigated. The results obtained were as follows:(1) When Al and Be were added simultanously, the maximum aged hardness obtained was the average of those of the single additions. The precipitated phases were NiAl and NiBe, both being CsCI type. The hardening was considered due to formation of clusters with ordered structure and also to precipitation of NiAl.(2) When Be and Ti were added simultanously, the age hardening effect was found to be additive and NiBe and Ni₃Ti phases were separately recognized in the electro-chemically extracted residue.(3) When Al and Ti were both added, fine spherical Ni₂AlTi phase was precipitated and the hardness increase due to aging was remarkable.(4) Even if 24% Cr was added to Fe-4% Ni alloys, the combined effect of Al was also recognized. The precipitated phase of Fe-24% Cr-4% Ni-Ti alloy was mainly X phase.