Effect of severe deformation on the microstructure and properties of Nd-Fe-B powders caused by hydrostatic extrusion

[Display omitted] •Consolidation of Nd-Fe-B powder by hydrostatic extrusion at room temperature.•The strong local defecting of the Nd2Fe14B creates a new phase.•Structural changes occurring in Nd-Fe-B involve a permanent reduction in the magnetic properties. The commercial Nd-Fe-B (Magnequentch MQU-F42) powder was consolidated by hydrostatic extrusion at room temperature in three stages. The values of thru strain obtained after the stages, were 1.38, 2.27, 3.12. A high degree of deformation leads to local changes occurring in the microstructure of the material that negatively affects its magnetic properties. Mossbauer spectroscopy has shown that a new phase appears in the deformed material, most probably as a result of strong local defecting (amorphization) of the Nd2Fe14B phase. Rietveld analysis of the diffraction phase investigation results indicates that deformation leads to a clear fragmentation of the material grain and to the deformation (change of parameters) of the crystal lattice. The heating of deformed materials leads to a series of irreversible transformations that start at a temperature of about 200 °C. As a result, α-Fe is produced from the defected phase in the form of 3 nm crystallites. The release of free Fe changes the chemical composition of the 'defected phase', making it impossible for it to revert to the structure prior to deformation. It can be concluded that the structural changes occurring in Nd-Fe-B powders during severe deformation are irreversible and involve a permanent reduction in the magnetic properties of the material.