Evaluation of process variables in the alignment factor of Nd-Fe-B magnets made by metal injection molding

Permanent Nd-Fe-B sintered magnets were fabricated with the metal injection molding technique. The alloy powder was mixed with a multi-component binder system, generating a feedstock that was injection molded into cube-shaped samples, under magnetic field for crystallographic texture development. Subsequently, samples underwent binder extraction in two stages (chemical and thermal) and were sintered under high vacuum. This study is focused on the effect of process variables on the magnet's texture. The texture degree, expressed by the alignment factor f(phi), was evaluated by analyzing the second quadrant of hysteresis curve. As expected, results show that magnetic field intensity during injection molding plays an important role on particle alignment, but acts in combination with particle mobility, which in turn, is dictated by the other process variables. For example, by increasing feedstock's viscosity and powder loading, the alignment factor, and consequently the remanence, decreases. In optimized conditions it is possible to obtain an alignment factor of 95%, above uniaxially pressed, sintered Nd-Fe-B magnets, resulting in elevated flux density magnets.