Coercivity and Phase Evolution in Mechanically Milled (FeCo) 2 B-Type Hard Magnetic Alloy

Two types of re-substituted (FeCo) 2 B-type alloys with stoichiometric (Fe 0.675 Co 0.3 Re 0.025 ) 2 B and 1.5 at% boron-excess compositions were prepared by suction casting and subsequent mechanical milling and annealing. Phase evolution in the (FeCo) 2 B-type alloys in the course of mechanical milling and annealing was investigated. Single-phase re-substituted (FeCo) 2 B-type material was prepared from stoichiometric (Fe 0.675 Co 0.3 Re 0.025 ) 2 B by the combination of suction casting and mechanical milling. The two alloys had the same phase constitution of (Fe, Co) 2 B-type and amorphous phases in heavily milled state. However, the heavily milled alloys had different phase constitution after annealing; the stoichiometric alloy consisted of single (Fe, Co) 2 B-type phase, while the boron-excess alloy consisted of two-phase mixture of (Fe, Co) 2 B-type and (Fe, Co)B-type phases. The two heavily milled alloys had similar coercivity of around 1 kOe after full annealing.