RAPIDLY SOLIDIFIED ALLOYS OF IRON - RARE-EARTH - BORON FOR PERMANENT MAGNETS (COERCIVE FORCE, HYSTERESIS, ANISOTROPY, PRASEODYMIUM, MELT SPINNING)

The effects of composition and processing variables on the magnetic properties of rapidly solidified iron-rare earth-boron alloys have been explored using a vibrating sample magnetometer. Additionally, supporting microstructural analyses are given to help explain the observed variations. This work has concentrated on producing large intrinsic coercivities, i.e., greater than about 10 kOe, directly at controlled solidification rates in melt spinning.;Variations in processing are shown to produce material inhomogeneities that have corresponding detrimental effects on coercivity. The expected variation in solidification rate through the thickness of the melt spun materials is demonstrated also to yield variations through the thickness in grain size and coercivity.;Moderate substitutions of cobalt for iron in alloys based on (Fe(,100-x)Co(,x))(,76)Pr(,16)B(,8) are shown to significantly raise the Curie temperature of the tetragonal phase and produce corresponding increases in the temperature coefficients of remanence and coercivity.;Intrinsic coercivities of only 100 - 1000 Oe are obtained at the lowest (0-4 m/s) and highest (40-80 m/s) wheel surface speeds in all alloys investigated. Intrinsic coercivities over 20 kOe have been obtained at intermediate wheel surface speeds (20-30 m/s) in alloys of Fe(,76)R(,16)B(,8) where R is praseodymium or neodymium. Typical hysteresis loops are also given. Substituting samarium and cerium for praseodymium and neodymium does not lead to large intrinsic coercivities at all wheel surface speeds. Replacements of boron with the metalloids carbon or silicon are also ineffective in producing large intrinsic coercivities. The phase responsible for the large coercivities has been identified as a tetragonal phase with a = 0.881 nm and c = 1.178 nm. The Curie temperature of the phase is shown to be about 285(DEGREES)C. The optimum coercivity found at intermediate wheel surface speeds has been shown to be due to the refinement of the microstructure to a grain size approximately 50 nm- 1 (mu)m in diameter. The coercivity mechanism is observed to be reverse domain nucleation.