Phase changes in Fe-rich Sm-Fe-V-Zr alloys

This paper describes the effect of Zr additions on phase changes in Sm-Fe-V system, around the compound Sm3(Fe,V)29. In SmxFe94.2-x-yV5.8Zry (x=7.7-8.9, y=0-1.6) alloys homogenized at temperatures above 1453 K, the hexagonal Th2Ni17-type (2-17H) phase, which was not observed in the ternary alloys, is present as the main phase. The amount of 2-17H phase increases and the amount of α-(Fe,V) decreases with increasing Sm content, after homogenization at temperatures above 1453 K. However, in the alloys homogenized at temperatures below 1373 K, the 2-17H phase is not observed and the Sm3(Fe,V)29-type (3-29) and Th2Zn17-type (2-17R) phases are present, accompanied by a small amount of ThMn12-type (1-12) phase, in which α-(Fe,V) is embedded. In Sm77Fe85.3V5.8Zr1.2 and Sm8.2Fe84.8V5.8Zr1.2 alloys homogenized at 1473 K for 20 h, X-ray diffraction (XRD) showed that the 2-17H phase transforms into 3-29 and TbCu7-type (1-7) phases after annealing for 4 h up to 1323 K, and into 3-29 and 2-17R after annealing at 1423 K. Transmission electron microscopy (TEM) observations then revealed that these grains consist of a submicron scale, two phase mixture. XRD studies showed that for Sm8.2Fe84.8V5.8Zr1.2 alloys homogenized at 1473 K for 20 h, subsequent annealing at 1323 K for 1 min-12 h causes the following phase changes: 2-17H → 3-29+1-7 → 3-29+2-17R, with increasing annealing time. The two phase microstructure described above was mainly observed in alloys composed of 3-29 and 1-7 phases, and it coarsened and gradually disappeared with increasing annealing time. This is the first report of two phase decomposition in the Sm-Fe-V system, however, the coercivities of the nitrided alloys in which a two phase mixture was observed, were small. (orig.)