The effect of evolving grain shape and alignment on the coercivity in thermomechanically deformed Nd-13.9(Fe-0.92 Co-0.08)(80.3) B5.3Ga0.5 permanent magnets

A series of samples of nominally identical composition have been melt-quenc hed and thermomechanically deformed to varying degrees, resulting in a vari ation in crystallographic alignment. The effect of the alignment on the coe rcivity has been studied using measurements of the temperature dependence o f coercivity. The analysis was performed using a well-known phenomenologica l model which relates the coercivity to the anisotropy field, through a par ameter alpha, and the saturation magnetization, through an effective demagn etization coefficient N-eff. It was discovered that the trends in alpha and N-eff as a function of crystallographic grain alignment are the opposite t o what is expected and measured previously in analogous sintered samples of varying crystallographic alignment. An explanation for this behavior is pr oposed in which the evolving grain shape and grain boundary topography caus ed by deformation becomes the controlling factor in the coercivity rather t han the crystallographic alignment of the grains. (C) 2001 Elsevier Science B.V. All rights reserved.