Ultrasonic Response in Nd-Fe-B Sintered Material During Elastic Deformation
The rare earth material based on Nd-Fe-B alloy shows remarkable magnetic properties in the energy product (BH)max and coercive force. It is manufactured by pressing in a unidirectional magnetic field to align the easy axes, and then sintering, leading to a large magnetic and mechanical anisotropy between the normal and parallel directions. The material is first developed by Croat  and Sagawa  independently in 1984. Following them, many researchers [3–6] have studied the material. They concentrated the efforts on the investigation of the manufacturing process to have better magnetic properties as well as on the observation of the microstructure to understand the mechanism realizing the high coercive force. The previous studies showed that the material consists of the major phase of Nd2Fe14B grains and the boundary phase of the Nd-rich alloys. It is considered that their different melting points and different thermal expansion coefficients introduce microcracks during the cooling process after sintering.