Role of precipitation in strength and ductility of FeCo-2V-Cr alloy with low coercivity

Improvement of the creep resistance of FeCo–2V alloy arising from a small addition of Cr

“…Obviously, the precipitates with fcc/hcp structure are Co-enriched. Our previous work [10] has shown that the precipitates only have bcc structure for the alloy annealed at 800 C for 2 h. As mentioned above, the samples subjected to the creep tests are those after the annealing process. In addition, the bcc precipitates observed in the crept sample exhibits the same lattice constant as that of the precipitates prior to the creep test.…”

“…Following the homogenized annealing at 1200 C for 4 h in a vacuum of 10 À4 Pa, the ingots were forged and hot-rolled at 1100 C to the plates with a thickness of 3 mm. The plates were then cold-rolled to 2 mm in thickness with a reduction of 30%, followed by an annealing in vacuum at 800 C for 2 h. The annealed Cr-added samples have been found to have a number of bcc precipitates existing in FeCobcc matrix, whereas there is no indication of precipitation in annealed Cr-free samples [10]. Then creep tests were performed for the annealed alloys at 600 C under a constant load ranging from 175 to 275 MPa on mechanical high temperature creep and rupture testing machine (CTM304-A1).…”

“…Lattice mismatch at the interface of precipitates and matrix was suggested to give rise to a repulsive elastic interaction which adds to the resistant force against dislocation movements even at high temperatures [9]. In our previous work, it has been also found that addition of a very small amount of Cr to FeCoe2V alloy combined with appropriate heat treatment leads to a remarkable improvement in tensile strength and ductility while maintaining their excellent soft magnetic properties [10,11], owing to a certain amount of fine bcc precipitates existing in the matrix of FeCoe2V alloy. It further reveals that the precipitates play a key role in hindering dislocation movement [10].…”