Grain growth behavior in Fe3Al alloys fabricated by different methods

Abstract

Grain sizes were measured after various heat treatments in three Fe3Al alloys having similar composition that were fabricated using the techniques of ingot metallurgy (cast and wrought), hot extrusion of prealloyed powder, and hot isostatic pressing (HIP) of elemental powders. The ingot metallurgy (I/M) material exhibited normal grain growth behavior at temperatures above 750 °C, in agreement with previous observations. Both powder metallurgy (P/M) materials displayed unusual resistance to grain growth compared to the I/M alloy. In the case of the prealloyed P/M material, the initial (recrystallized) grain size was larger than the initial grain size of the I/M material, although little grain growth was observed for heat-treatment temperatures up to 1100 °C. At higher temperatures grain growth occurred at a rate comparable to that observed to the I/M alloy. The elemental powder P/M material exhibited similar grain growth behavior to the prealloyed P/M material, although the initial (as-HIPed) grain size was considerably smaller. Transmission electron microscopy (TEM) indicated that the grain growth resistance of the P/M materials could be attributed to grain boundary pinning by oxide particles presumed to originate from the powder particle surfaces. The difference in the stable grain size between the prealloyed and elemental powder P/M materials was attributed to the nature of the particle dispersions resulting from processing.