Microstructural and Texture Evolution of Strip Cast Nd-Fe-B Flake
In this work, the microstructure and texture evolution of the strip cast Nd-Fe-B flake has been systematically investigated by correlating multiple state-of-the-art characterization techniques. We found that (i) besides the existence of random ultrafine equiaxed grains at the wheel side of the flake, elongated (001) textured grains were formed into a V-shape zone between neighboring nucleation sites, which possibly resulted from the in-plane growth of the low energy preferred growth direction of grains (a axis). Both ultrafine random equiaxed grains and elongated (001) textured grains are detrimental to achieving a high-performance Nd-Fe-B magnet, due to the inhomogeneous grain shape and nonuniform distribution of rare earth-rich phase within these grains or along the grain boundaries, which deteriorate the alignment of the Nd-Fe-B powders in the subsequent hydrogen decrepitation process and jet milling procedure. To overcome the issues mentioned above, two potential approaches are proposed, which are increasing the nucleation rate on the wheel side and homogenization of rare earth-rich phase within grains or along grain boundaries; (ii) columnar grains containing (Nd,Pr)2Fe14B lamellae with an average spacing of ∼5 μm and discontinuous rare-earth rich phase were formed in the remaining part of the flake. Accordingly, a model in terms of the microstructure and texture evolution was proposed.