ANISOTROPIC THERMAL EXPANSION AND FRACTURE OF RADIALLY ORIENTED TOROIDS OF RE-Co PERMANENT MAGNETS

The mechanism of the fracture of radially oriented toriods of sintered SmCo_5has been investigated. It showed that the fracture of radially oriented toroids af-ter sintering may be caused by wild anisotropy of thermal expansion. An expres-sion of orientability in critic fracture has been derived. Their orientability notonly calculated by this expression but also obtained from experiments should notbe more than 0.7. The anisotropic behaviour of their thermal expansion may bemarkedly reduced by a partial substitution of Cu for Co and a shift of its com-position toward the Co enriched 2-17 phase region. Noticeably, both Sm(Co_(0.80)Cu_(0.14)Fe_(0.06)), and Sm(Co_(0.87)Cu_(0.13))_8 are almost completely isotropic. It seems thatthey are the ideal materials for radially oriented toroids of best performace. Theorigin of anisotropy of thermal expansion has been further discussed and that thepossibility of Cu atoms partially substituting the 2c sites in Sm (Co,Cu)_5 was sug-gested.