Improvement of mechanical workability and constancy of permeability of Fe-Ni-Si alloy by splat cooling technique

Iron-rich alloy ribbons containing about 15 wt % nickel and 12 wt % silicon, which have been called Senperm, were prepared in the crystalline state using a single roller quenching method. The ribbons were remarkably flexible and had a silver-white lustre. They were not oxidized even if they were left in the air for a few months. They could not be bent 180° the minimum winding diameter was 6 mm. The magnetic properties were measured with an open magnetic circuit apparatus and an LCR-meter. The magnetic properties of the as-prepared ribbons were: initial permeability μi=500 and the range of constant permeability Hi=0.25 Oe for SP-No.1; μi=250 and Hi=1.4 Oe for SP-No.2. After annealing at 900°C for a few hours in a vacumm, the ribbons became more flexible and could be bent 180° easily. The minimum winding diameter decreased to 1.2 mm. The magnetic properties were improved noticeably and were: μi=350, Hi=0.6 Oe for SP-No.1 and μi=50, Hi=2.7 Oe for SP-No.2. It was also confirmed that μi was nearly constant up to 50 kHz. The grain strucrure was observed using a 25 kV scanning electron microscope.