Microstructure and magnetic properties of Mn-Al-C alloy powders prepared by ball milling

Magnetically anisotropic Mn-Al-C powders have been prepared by ball milling the tau-phase Mn53.3Al45C1.7 alloy. Flake-shaped powders were obtained after milling for 2 h and the thickness decreased continuously with extended milling time. No sign of decomposition was observed in the as-milled state, however, magnetization decreased and coercivity increased continuously with milling time because of the defects introduced in the milling process. mu H-0i(c) of 0.52 T was obtained in powders milled for 12 h. By annealing the as-milled powders at 773 K for 30 min, the magnetization increased significantly because of the recovered crystal structure of tau-phase. A degree of texture ranging from 17.8% to 37.1% has been obtained and the magnetically easy axis lies within the plane of the flakes. Optimized magnetic properties, with M-r of 54.8 Am-2 kg(-1) and mu H-0i(c) of 0.28 T, was obtained in Mn53.3Al45C1.7 powders milled for 5 h followed by heat treatment at 773 K.