Executive Summary : | Nd-Fe-B permanents magnets are workhorses in many applications such as electronic devices, automobiles, industrial application etc. The low coercivity (Hc) (~1.2 T) of NdFeB magnet is of a major concern as it further deteriorates at higher temperature making the magnet unusable at about 150 ºC, which is the typical operating temperature of motor application. The magnetic isolation of Nd2Fe14B grains by non-ferromagnetic species along the grain boundaries (GBs) by means of grain boundary diffusion process (GBDP) involving low-melting eutectic alloys reduces the exchange interactions and thereby increases the coercivity of NdFeB significantly. Conventionally binary low melting eutectics such as Nd-X (X=Cu, Al etc.) are used in GBDP in enhance the coercivity of the magnet but this process of improvement in Hc is always accompanied by reduction in saturation magnetization (Ms) and remanence (Br) which are equally crucial in designing a good magnet. In this context, tailoring composition of conventional eutectic with minor addition of ferromagnetic elements such Fe, Co would facilitate simultaneous enhancement in Hc, Ms and Br. So, the overall objective of this work is to decorate the NdFeB melt spun ribbons by the grain boundary diffusion of champion Nd1-(x+y)Cux(Fe, Co)y alloy and thereby enhancing magnetic properties for target applications. The proposed gradient of eutectics will be designed and developed by combinatorial alloy design where in a custom-designed vacuum induction melting setup enabling the processing of multiple sample variants will be used, which will be a novel technique for developing low melting eutectics. The combinatorial approach of rapid alloy prototyping facilitates the development of cast ingots with gradient low melting eutectic alloy compositions produced from a single master melt. The grain boundary diffusion process (GBDP) of the champion eutectic will be carried out by suitable heat treatment process in the pulverized melt spun ribbon. The magnetic properties of this GBDP melt spun ribbon will be compared with that of GBDP commercial sintered permanent magnet infiltrated with the same champion eutectic alloy. Correlative microscopic approach will be adopted to characterize a specific region of interest (GB in this study) at different length scales starting from bulk scale to nano scale analysis combining SEM-EDS, EBSD, atom probe tomography (APT), transmission Kikuchi diffraction (TKD) and TEM in order to understand the grain boundary diffusion processes and sintering mechanisms. |