Plasma sprayed Nd–Fe–B permanent magnets

This study demonstrated that the plasma spray deposition method is an alternative process for producing Nd–Fe–B magnets in addition to the two existing principal processes: the powder metallurgy process for producing sintered Nd–Fe–B magnets and the melt spinning process for bonded Nd–Fe–B magnets. Plasma spray is a potentially better process for producing magnetic parts with complicated shape, large area, thin thickness, small dimension, or unusual geometry. High intrinsic coercivity greater than 15 kOe was readily obtained for Nd16Dy1Fe76B7 even in the as-deposited condition when the substrate was preheated. The plasma spray process contains only three steps: melting, crushing, and plasma spray, which is much simpler than the powder metallurgy and melt spinning processes. Without preheating the substrate, the coercivity was usually very low (∼0.1 kOe) in the as-deposited condition and it increased to 10 to >15 kOe after anneal. Evidence of magnetocrystalline anisotropy was observed in plasma sprayed Nd15Dy1Fe77B7 magnets when the substrate was not preheated. It is believed that a crystal texture was developed during the plasma spray as a result of the existence of a temperature gradient in the solidifying melt.