Nects of hot isothermal pressing on the microstructures and soft magnetic properties of nanocrystalline Fe86Zr7B6Cu1 ribbons

The effects of hot isothermal pressing (HIP) on the microstructures and soft magnetic properties of nanocrystalline Fe86Zr7B6Cu1 ribbons were studied. Amorphous Fe86Zr7B6Cu1 ribbons were annealed at 600degreesC for 1 h by HIP under pressures in the range of 0-150 MPa. It is shown that hot isothermal pressure results in a marked decrease in grain size of bcc alpha-Fe and a distinct improvement in soft magnetic properties. An increase in pressure from 0 to 150 MPa leads to a decrease of grain size from 13.2 to 7.3 nm, a decrease in coercive force from 15.8 to 1.8 A m(-1), an increase in initial permeability from 1.2 x 10(4) to 6.3 x 10(4), and a decrease in relaxation frequency from 2.5 x 10(5) to 5.1 X 10(4) Hz. The decrease in grain size may result from the fact that pressure promotes nucleation of the alpha-Fe phase and constrains its growth during the crystallization process.