THE EFFECT OF MICROSTRUCTURAL EVOLUTION ON THE COERCIVITY DEVELOPMENT OF PT-CO-B ALLOYS

The undercool-rapid-quench (URQ) processing of Pt42Co45B13 (at. %) (Pt-Co-B) alloys with subsequent annealing produced an intrinsic coercivity (H(ic)) as high as 15.7 kOe. The evolution of H(ic) during heat treatment is related to the initial URQ-processed microstructure and its influence on the annealing phase transformations. Higher solidification rates refine the dendrites, decrease the interdendritic volume fraction, and enrich the interdendritic boron concentration. Annealing the materials processed with a higher quenching rate leads to more rapid interdendritic decomposition with more refined transformation products and a concomitant larger increase in H(ic). The high H(ic) in Pt-Co-B alloys originates mainly from difficult magnetic domain nucleation owing to limited nucleation sites in magnetic single-domain size Co3B precipitates and an ordered magnetic anisotropic matrix with few defects such as antiphase domain boundaries and twins.