Relationship between the thermal stability of coercivity and the aspect ratio of grains in Nd-Fe-B magnets: Experimental and numerical approaches. (15th January 2020)

• Record Type: Journal Article
• Authors: Tang, Xin; Li, J.; Miyazaki, Y.; Sepehri-Amin, H.; Ohkubo, T.; Schrefl, T.; Hono, K.
• Is Part Of: Acta materialia. Volume 183(2020)
• Page Start: 408
• Page End: 417
• Publication Date: 2020-01-15
• Subjects: Nd-Fe-B magnets -- Hot-deformed magnets -- Coercivity -- Thermal stability -- Micromagnetic simulations; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2019.11.038
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract : The influence of the aspect ratio of grains on the thermal stability of coercivity of Nd-Fe-B hot-deformed magnets was systematically investigated by experimental and numerical approaches. With increasing amount of Nb doping from 0.2 at.% to 0.6 at.% in the hot-deformed magnets, the aspect ratio of grains, defined as the ratio of the width to the height of a Nd2 Fe14 B grain ( D c / D ab ), decreased while the average grain size was preserved. No change of temperature coefficient of coercivity ( β ) was observed in the as hot-deformed samples with different grain aspect ratios. However, the reduction of aspect ratio (increase of the height and reduction of the width of platelet shaped Nd2 Fe14 B grains) improves β for the sample infiltrated with a Nd-Cu eutectic alloy; i.e., from β = −0.42 %/°C to −0.40 %/°C for the aspect ratio reduction from 4.7 to 3.1. Micromagnetic simulations indicated that the grain aspect ratio is not a dominant factor to the thermal stability of coercivity for exchange-coupled anisotropic polycrystals. While smaller aspect ratio reduces demagnetizing field caused by magnetically isolated grains, resulting in the improvement of the thermal stability of the coercivity for Nd-Cu infiltrated hot-deformed magnets. Graphical abstract: Image, graphical abstract