Preparation And Study Of High Temperature Aging Of Sm Co Magnets And Their Protective Films

The field of National defense has requirements for permanent magnets capable of operating at temperature≥400℃. The Sm2Co17-style magnets become the most promising choice for permanent magnet application at high temperatures because of their high Curie temperature, high coercivity, high magnetic energy product, and good corrosion resistance.However, the formation of the surface degradation layer results in an irreversible loss of magnetic properties at such high temperatures. So far, the formation mechanism of the surface degradation layer of SmCo-based magnets at high temperatures is still controversial. Furthermore, the successful coatings for SmCo-based magnets have been still lacking.This paper studied the isothermal aging behavior of Sm2Co17magnets in air at500℃,600℃and700℃. The results show that the formation of surface degradation layer caused the decline of magnetic properties, and the thickness of surface degradation increase gradually with the increase of aging temperature (or the extension of aging time). In order to discuss the main reason for the formation of surface degradation layer, the isothermal aging behavior of Sm2Co17magnets in vacuum at500℃also was investigated. The results show that the oxygen diffusion, but not the vaporization of Sm, is the main reason of the formation of surface degradation layer. In view of the oxygen diffusion, this paper developed NiCrAlY film and NiCrAlY/AlO3composite film to protect the Sm2Co17magnets. The protection performance of thin films was studied.In this paper, the NiCrAlY film and the amorphous Al2O3film were deposited by DC magnetion sputtering and DC pulsed magnetron sputtering, respectively. The deposition process of NiCrAlY film and NiCrAlY/Al2O3films were optimized. The results show that the NiCrAlY film can effectively protective Sm2Co17magnets in air at temperature≤500℃.However, the diffusion rate of Oxygen element in NiCrAlY film over600℃, and the interdiffusion between the NiCrAlY film and matrix of magnets become serious. Thus, the structure of NiCrAlY film was unstable over and the protective effect of NiCrAlY film is not good in air over600℃. Moreover, the protactive effect of NiCrAlY/Al2O3films for Sm2jCo17magnets is very good and the structure of composite film has a stable structure in air at600℃.