Abstract
The microstructures of Sm2Fe17 alloys heat-treated in hydrogen and subsequently in a vacuum were observed by transmission electron microscopy (TEM). Sm2Fe17 alloys heat-treated in hydrogen at 600°C for 60 min showed a disproportionate reaction and had a microstructure composed of rod-shaped SmH2 grains and α-Fe. Hydrogen treatment at high temperature (850°C) caused grain growth, and SmH2 grains of 20-100 nm in diameter were observed embedded in an α-Fe matrix. Microstructural observations of the alloy heat-treated in a vacuum at 775°C for 5 min revealed the following recombination reaction process: Fe atoms diffuse into SmH2 grains and react with Sm atoms, resulting in the formation of an Sm2Fe17 compound. After heat treatment in a vacuum at 775°C for 30 min, the recombination reaction is already complete, and the Sm2Fe17 grains have grown to a size of 150-300 nm.
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