Microstructural and Magnetic Properties of Nanocrystalline Nd-Fe-B Rare Earth Magnet Prepared by Spark Plasma Sintering Technique

Abstract

A study was carried out to prepare a magnet with a c-axis alignment present in the melt-spun ribbons to be used as a precursor magnet for the hot deformation process. Melt-spun ribbons prepared at a wheel speed of 23 m/s resulted in nanograins with columnar grains having the <001> texture on the exposed side and very fine equiaxed nanograins on the wheel side of the ribbon. The ribbons were stacked and consolidated using the SPS technique with the variation of temperature (temperature series) and pressure (pressure series), which resulted in Nd₂Fe₁₄B grains in two-grain zones, namely (i) fine grain and (ii) coarse grain zones. The fine grains grow with temperature and dominate the coercivity mechanism in the temperature series, and the grains do not grow in the pressure series; hence, the coercivity is not affected by pressure. The calculation of the intensity ratio of I₍₀₀₆₎/I₍₁₀₅₎ in SPS compacted samples in both temperature and pressure series showed evidence of texture retention; however, the texture was not strong enough to influence the magnetic properties. The best magnetic properties of H_c of 12.2 kOe and (BH)_max of 11.6 MGOe were obtained in the temperature series sample prepared at temperature of 600 °C, pressure of 150 MPa, and dwell time of 2 min.