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Microstructure and temperature dependent of coercivity of hot-deformed Nd–Fe–B magnets diffusion processed with Pr–Cu alloy

Acta Materialia

2015年9月4日(金)

Acta Materialia ( Volume 99, 15 October 2015, Pages 297–306 )
H. Sepehri-Amin, Lihua Liu, T. Ohkubo, M. Yano, T. Shoji, A. Kato, T. Schrefl, K. Hono

Abstract

The coercivity of hot-deformed Nd–Fe–B magnet was substantially enhanced from 1.0 T to 2.6 T by the grain boundary diffusion process using Pr–Cu alloy. However, the temperature dependence of coercivity is larger compared to the sample diffusion processed with Nd–Cu. Microstructure studies showed a good isolation of platelet shaped Nd2Fe14B grains by Pr-rich intergranular phase, which explains pronounced coercivity at room temperature. Small portions of Nd2Fe14B become (Nd,Pr)2Fe14B phase, which has a higher anisotropy field compared to that of the Nd2Fe14B phase at room temperature, while it becomes lower than that of the Nd2Fe14B phase above ∼110 °C. Co is depleted from the (Nd,Pr)2Fe14B phase, which is considered to cause a slight decrease in Curie temperature. Micromagnetic simulations with the magnetically isolated grains including (Nd,Pr)2Fe14B regions showed that the degradation of thermal stability of coercivity in the Pr–Cu diffusion processed sample is due to the large temperature dependence of anisotropy field in the (Nd,Pr)2Fe14B regions.

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