High coercivity, isotropic plasma sprayed samarium-cobalt magnets

Abstract

A value of 67.5 kOe has been measured for the room temperature coercivity of an isotropic, heat treated, 1‐5 samarium‐cobalt plasma sprayed deposit. This value is believed to be the largest published, so far, for a permanent magnet. Sprayed magnets are generally found to be better than 93 percent dense with coercivities of 35 to 60 kOe. Deposits comprised of fine microstructures yield broad, unresolved x‐ray diffraction peaks. Low temperature crystallization of these deposits yields diffraction patterns representative of the high temperature equilibrium structure. The emergence of peaks, ascribed to SmCo₅, from a low temperature 700 °C heat treatment implies both formation and stability of the SmCo₅ phase at this temperature. These results dispute the existence of the generally accepted eutectoid decomposition reaction for SmCo₅ at 750–800 °C. If such a reaction were present the products of crystallization should have included Sm₂Co₇ and not SmCo₅. High temperature investigations on sprayed magnets indicate that temperatures of 1100 °C result in low values of coercivity, possibly due to grain growth.