Microstructural and magnetic improvements in tube-cast Pr-Fe-B-Cu alloys via heat treatments and rapid upset forging

摘要

Alloys of Pr-Fe-B-Cu were cast into Cu and stainless steel tubes. It could be seen that a preferred crystallographic orientation was obtained after cooling. Fine platelets of Pr_2Fe_(14)B matrix phase were formed, surrounded by various grain boundary phases, and there was a significant reduction in the amount of free Fe present, in comparison to conventional slab cast alloys. In order to improve the magnetic properties in the as-cast state, two alternative routes were used. The first involved a series of two step heat treatments to develop an improved microstructure. After an optimum heat treatment of 1000 deg C for 24 hours + 500 deg C for 3 hours, significantly improved magnetic properties were obtained for a 17.5 percent Pr alloy; B_r = 752 mT, H_(ci) = 613 kAm~(-1) and BH_(max) = 96 kJm~(-3). The second route involved a rapid upset forging [RUF] process, with a strain rate of 11.5 s~(-1), to hot deform the alloys. Following post-forging heat treatments, properties of B_r = 966 mT, H_(ci) = 780 kAm~(-1) and BH_(max) = 160 kJm~(-3) were obtained for a 15percent Pr alloy. That nature of the improvements in properties as a result of heat treatments and RUF were investigated and are discussed in the present work.