Executive Summary : | The necessity for the design and development of sintered permanent magnets with defined grain boundary (GB) additives have increased significantly owing to the following two critical factors, 1. Persistent increase in prices of strategic rate-earth (RE) reserves such as Nd and Dy. 2. Requirement for higher operating temperatures of the sintered permanent magnets for critical applications. Not many well-defined grain boundary additives are available to overcome the above challenges. This situation is mainly due to the limitation in the availability of relevant data including thermodynamic database for prediction eutectic phases and their compositions involving RE elements. To overcome these challenges, the proposal intends to explore wide-range of eutectic alloys containing RE elements by the method of accelerated exploration of materials called “Combinatorial Materials Design (CAD)”. CAD enables in the synthesis of a well-defined range of compositions in a single melt-casting process thereby all associated synthesis parameters remain constant. In addition, a library of compositions with uniform gradient can also be obtained from a single master melt using the CAD method facilitating accelerated exploration of potential alloys exhibiting the required properties with limited of materials expenditure for their use as GB additives in sintered magnets. Upon identification of the champion GB additive alloy, it would be processed in the form of thin sheets of varying thicknesses and attempted for GB diffusion using ‘diffusion rolling (DR)’ process. DR process involves back and forth rolling of a packed assembly consisting of GB additive plates sandwiching the permanent magnet at various temperatures and controlled stress levels. Under optimum conditions of temperature and stress, this process would enable in the extended diffusion of GB additives in the sintered permanent magnets there by decorating majority of GBs which would then facilitate in the pinning of magnetic domains. Primitive magnets in different forms and DR magnets would be subjected to multi-scale characterisation involving XRD, EBSD/TKD, TEM and APT to identify the major phases present and to distinguish the GB phases formed. Correlative microscopy analysis would be performed to understand the degree of elemental segregation as a function of GB energy. Further, the macroscopic degrees of freedom associated with defect structures present in the sintered magnets would be investigated to determine the maximum possible extent to which additives can be included by DR process. Both the primitive and GB decorated permanent magnets would be studied for their magnetic properties especially the enhancement in coercivity in the presence of additives and their temperature dependence. This comprehensive effort hence offers the potential of developing novel additives suitable for the development of next-generation high performance permanent magnets. |