Study of phases evolution in high-coercive MnAl powders obtained through short milling time of gas-atomized particles

摘要

Gas-atomized Mn54Al46 particles constituted nominally of only epsilon- and gamma 2-phases, i.e. no content of the ferromagnetic Llo-type tau-phase, have been used to study the evolution of phases during short time of high-energy milling and subsequent annealing. Milling for 3 min is sufficient to begin formation of the tau-MnAl phase. A large coercivity of 4.9 kOe has been obtained in milled powder after annealing at 355 degrees C for 10 min. The large increase in coercivity, by comparison with the lower value of 1.8 kOe obtained for the starting material after the same annealing conditions, is attributed to the combined formation of the tau-MnAl and beta-Mn phases and the creation of a very fine microstructure with grain sizes on the order of 20 nm. Correlation between morphology, microstructure and magnetic properties of the rapidly milled MnAl powders constitutes a technological advance to prepare highly coercive MnAI powders. (C) 2017 Elsevier B.V. All rights reserved.