The effect of ternary additions on the vacancy hardening of FeAl

Abstract

It is now well-established that following high temperature heat treatments a high concentration of vacancies can be retained in ordered b.c.c. (or B2-structured) compound FeAl at room temperature, even following furnace cooling. This can result in a substantial increase in hardness, and a concomitant decrease in ductility. This anomalous hardening can be relieved by low temperature (400 C) aging during which the excess vacancies are removed. In a previous study it was shown that small nickel additions (< 1 at.%) can partially suppress the significant hardening effect in near-stoichiometric FeAl following high temperature annealing. However, these additions also produced significant increases in the equilibrium hardness following low temperature vacancy-relieving heat treatments. Further studies on these alloys revealed some compositional anomalies which may have affected some data. These previous studies were repeated and the revised data are presented. In addition, the effect of other transition metal ternary additions on vacancy hardening effects in FeAl was studies. A range of alloys with nominal composition Fe[sub 49]Al[sub 50]X[sub 1] (X = Cu, Ni, Co, Mn, Cr, V, Ti) were prepared. These alloys were subjected to both high temperature annealing and subsequent vacancy-relieving heat treatment. Their behavior was monitored by microhardness measurements and theirmore » microstructure was examined by both optical microscopy and transmission electron microscopy.« less