Structural evolutions of the Fe–40Al–5Cr powders during mechanical alloying and subsequent heat treatment

Abstract

Nanocrystalline Fe–40Al–5Cr powders were synthesized by mechanical alloying (MA) of the Fe, Al elemental powders and the Fe–20Cr prealloyed powders. Structural evolutions, morphologies, composition homogenization and ordering transformation of the Fe–40Al–5Cr powders during MA and subsequently heat treatment were studied. In the early stage of MA (<15 h), solid solutions of Fe(Al) and Fe–Cr(Al) form through Al diffusing into Fe and Fe–20Cr, respectively. Layered Fe(Al)/Fe–Cr(Al) laminae are the typical structure of the milled powders. On prolonging the milling time from 15 to 70 h, the layered laminae disappear, and the milled powders turn to be dense, fine and spherical. Meanwhile, the composition homogenization of the milled powders is also gradually accomplished. After the Fe–40Al–5Cr powders milled for 70 h, nanocrystalline Fe(Al, Cr) powders form with a homogeneous composition. During heating the milled powders from room temperature to 600 °C, the ordering transformation from Fe(Al, Cr) to B2-FeAl(Cr) occurs. The Cr content in the Fe–40Al–5Cr powders was found to hinder the composition homogenization and ordering transformation of the powders during MA and subsequent heat treatment.