Variation in Microstructure of Ground SmCo₅ Alloy during Disproportionation in Hydrogen and Recombination

Abstract

Electron scanning microscopy and energy-dispersive X-ray spectroscopy are employed to examine the phase transformations and morphology of ground KS37 alloy (with SmCo₅ matrix) during solid hydrogenation, disproportionation, desorption, and recombination under 0.4 MPa hydrogen pressure and 950 °С. It is found that the ground alloy has cellular microstructure. The disproportionation of the ground alloy leads to samarium hydride and cobalt with nanosized grains (35–100 nm). It is established how the morphology of the disproportionation products depends on reaction parameters. The desorption and recombination result in a nanosized Sm₂Co₇ phase with 40–75 nm grains and a partially nanosized SmCo₅ phase with 45–140 nm grains. The mechanism whereby the nanostructure of ferromagnetic alloys forms through hydrogen mechanical and heat treatment is explained. It is based on the variation in morphology during hydrogen-initiated phase transformations and dependences such as grain size of the disproportionation products on grain size of the alloy before hydrogenation and grain size of the recombined alloy on grain size of the disproportionation products.