Relações de fases e propriedades magneticas nos sistemas Fe-R e Fe-R-B (R=Nd, Pr)

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

The phase relations and magnetic properties of the Fe-R and Fe-R-B (R = Nd, Pr) were studied by metallography, Differential Thermal Analysis, Hicro-analysis, X-Ray Diffractions and Coercivity Measurements. In the Fe-Nd system a new stable ferromagnetic phase with 22,7 % at .Nd and Tc = 231ºC is found. Rich-Nd Fe-Nd alloys and rich-Pr Fe-Pr alloys, solidify through a metastable eutectic reaction with ferromagnetic metastable phases precipitation which results in high coercivities. The oxygen contamination in the rich-Fe Fe-Pr alloys decomposes the Fe17Pr2 compound into Fe and Pr2O3. Also, in the Fe-Pr system a new phase with 2:3 ratio Fe:Pr, possibility stabilized by oxygen, is found. In the Fe-Nd-B ternary system the solidification in the neighborhood of the F-Pr-B was studied. A new ferromagnetic phase with Tc = 287 ± 3ºC is observed in the TMA measurements. A 700ºC isothermal section included the new binary phase was determined. Magnetic analysis shows two ferromagnetic phases with Tc = 246 and 287ºC in as-cast Nd-rich Fe-Nd-B alloys. Also, in the Fe-Pr-B system, magnetic analysis shows two ferromagnetic phases with Tc = 223 and 268ºC in as-cast Pr-rich alloys. For both ternary systems an annealing at 600ºC dissolves the phases with Tc = 246 or 223ºC and precipitates Fe14R2 B. This results in an Hc increase from 4,5 KOe in the as-cast to annealing condition for an Fe15Nd80B5 alloy, and from 15,5 KOe in the as-cast to above 18 KOe annealing condition for an Fe15Pr80B5 alloy. This suggests that the dissolution of the metastable phases and the presence of additional ferromagnetic phases in the intergranular regions of sintered Fe-R-B magnets might be the key factors in obtaining the high coercivities.

ASSUNTO(S)

materiais ferro - propriedades magneticas

ACESSO AO ARTIGO

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