Identifications of SmCo5 and Sm+1Co5−1-type phases in 2:17-type Sm-Co-Fe-Cu-Zr permanent magnets

Abstract Both SmCo5 and Smn+1Co5n−1-type phases were identified in the Sm25Co42.9Fe23.5Cu5.6Zr3.0 (wt.%) commercial sintered magnet even at the solution-treated state, with the 1:5H cell boundary phase occupying pyramidal planes, the 1:3R (n = 2) thin platelets occupying some basal planes, and the mixture of 1:3R, 2:7R (n = 3) and 5:19R (n = 4) phases distributing at grain boundaries. The mixed Smn + 1Co5n − 1-type phases at grain boundaries act as primary sinks and lead to sparse 1:5H-precipitates surrounding them after isothermal aging. It clearly reveals that the 1:5H cell boundaries are formed at the early decomposition stage and why they are rare at grain boundaries in the aged magnets.