Microstructural Investigation of Mixed Rare Earth Iron Boron Processed Via Melt-Spinning and High Pressure Gas-Atmoization for Isotropic Bonded Permanent Magnets.

Buelow, N. L.

Technical Information Center Oak Ridge Tennessee

关键词: Iron alloys;    Boron containing alloys;    Rare earths;    Magnets;    Microstructure;   

RP-ID  :  DE2006850076

学科分类：工程和技术（综合）

美国|英语

来源: National Technical Reports Library

【 摘 要 】

A solid solution of three rare earths (RE) in the RE(sub 2)Fe(sub 14)B structure have been combined to create the novel mixed rare earth iron boron (MRE(sub 2)Fe(sub 14)B) alloy family. MRE(sub 2)Fe(sub 14)B exhibits reduced temperature dependent magnetic properties; remanence and coercivity. The desired form of MRE(sub 2)Fe(sub 14)B is a powder that can be blended with a polymer binder and compression or injection molded to form an isotropic polymer bonded permanent magnet (PBM). Commercially, Nd(sub 2)Fe(sub 14)B is the alloy of choice for PBMs. Powders of Nd(sub 2)Fe(sub 14)B are made via melt-spinning as can be MRE(sub 2)Fe(sub 14)B which allows for direct comparisons. MRE(sub 2)Fe(sub 14)B made using melt-spinning at high wheel speeds is overquenched and must be annealed to an optimal hard magnetic state. Due to the rare earth content in the MRE(sub 2)Fe(sub 14)B powders, they must be protected from the environment in which they operate. This protection is accomplished by using a modified fluidized bed process to grow a protective fluoride coating nominally 15nm thick, to reduce air oxidation. MRE(sub 2)Fe(sub 14)B has demonstrated reduced temperature dependent magnetic properties in ribbon and PBM form. The real challenge has been modifying alloy designs that were successfully melt-spun to be compatible with high-pressure gas-atomization (HPGA). The cooling rates in HPGA are lower than melt-spinning, as the powders are quenched via convective cooling, compared to melt-spinning, which quenches initially by conductive cooling. Early alloy designs, in gas atomized and melt-spun form, did not have similar phase compositions or microstructures. Alloy additions, such as the addition of zirconium as a nucleation catalyst, were successful in creating similar phases and microstructures in the HPGA powders and melt-spun ribbon of the same MRE(sub 2)Fe(sub 14)B composition.