Phase transformations and magnetic properties of overquenched Pr7Fe88B5 ribbons during annealing have been investigated. X-ray diffraction and Mössbauer measurement indicate that melt spinning at different wheel velocities caused the as-quenched ribbons to have distinctive structures. Depending on their as-quenched structure, the phase transformation of the ribbons during annealing may take place in one of the following sequences: (1) amorphous phase (Am)+Pr2Fe14B+α-Fe→Pr2Fe14B+α-Fe; (2) Am+α-Fe→Am′+α-Fe→α-Fe+1:7 phase+Pr2Fe14B→Pr2Fe14B+α-Fe; and (3) Am→Am′+α-Fe→1:7 phase+α-Fe→Pr2Fe14B+α-Fe. In all cases, the microstructure of the ribbons after optimal annealing was found to only consist of two magnetic phases: Pr2Fe14B and α-Fe. However, with increasing initial quenching rate, the microstructure of optimally heat treated ribbons becomes coarser and more irregular, and the magnetic properties of them deteriorated drastically. The δM plots, irreversible susceptibility, and the temperature dependence of coercivity of the annealed ribbons were measured and analyzed. It was found that the coarser-grained and more irregular microstructures, as mentioned above, would lead to the weakening of the exchange coupling effect between the hard and soft phase, the inhomogeneous nucleation of reverse domain, a lower critical nucleation field, and a decrease in αex and Neff. These may be the reasons that the optimal magnetic properties of annealed ribbons reduce significantly with increasing initial quenching rate.

Effects of B and Cr additions on magnetostriction and the mechanical properties of polycrystalline Fe 83 Ga 17 alloy were investigated. Small addition of B increased magnetostriction of Fe 83 Ga 17 alloy slightly, and improved the room temperature ductility and tensile strength significantly. The elongation and tensile strength of the (Fe 83 Ga 17 ) 99 B 1 alloy increased to 3.56% and 548 MPa compared with that of Fe 83 Ga 17 alloy respectively. The Cr addition was shown to improve the room temperature mechanical properties of Fe 83 Ga 17 alloy beneficially. The maximum magnetostriction of (Fe 83 Ga 17 ) 98 Cr 2 alloy was 70 Â 10 À6 . The influences of B and Cr additions on the fracture mode of Fe 83 Ga 17 alloy were also studied in this paper.

No abstract

No abstract

The α-Fe/R2Fe14B-type nanocomposite magnets have been prepared by hot pressing melt spun Pr8Dy1Fe74.5Co10Nb0.5B6 flakes under a conventional pressure P of 125 MPa and high pressures ranging from 1 to 7 GPa. It was found that increasing compaction pressure from 125 MPa to 5 GPa led to marked grain refinement in the magnet and consequently resulted in significant improvement of magnetic properties. When hot pressing under even higher pressure (P>5 GPa), however, the crystallization was constrained and the hot pressed magnets retained a certain amount of amorphous phase besides the Pr2Fe14B-type phase and α-(FeCo) phase, which resulted in the deterioration of the magnetic properties. A remanence of 11.1 kG, coercivity of 10.2 kOe, and maximum energy product of 23.6 MGOe have been achieved in the magnet hot pressed under a pressure of 5 GPa.