The effect of cooling rate and heat treatment on hardness across the FeAl-NiAl pseudobinary

Abstract

Vacancies in binary ordered body-centered cubic, or B2-structured, intermetallic compounds, such as FeAl, NiAl and CoAl have been studied extensively. It is well-known that rapid quenching from elevated temperatures results in the retention of a high concentration of thermal vacancies. These retained vacancies can manifest themselves by means of increase in electrical resistance and hardness. Following subsequent low temperature annealing, the excess vacancies are removed and reductions in hardness and electrical resistance are observed, concomitant with this change faulted dislocation loops and voids are formed. It has recently been demonstrated that for FeAl in particular, the hardness is strongly dependent upon heat treatment, and a large number of vacancies are retained even following furnace cooling from elevated temperatures. In contrast, NiAl, although shown to retain a high concentration of vacancies following heat treatment, does not demonstrate such large increases in hardness. To investigate this phenomenon further a range of alloys were presented across the FeAl-NiAl pseudobinary, where the aluminum content was maintained at 50at.%. These alloys were subjected to a range of heat treatments followed by microhardness measurements. The purpose of this paper is to show the effect of heat treatment on hardness as a function of both composition andmore » heat treatment between equiatomic NiAl and FeAl.« less