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

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

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