Production of Fe-6.9 wt%Ti alloy sheets for application in electric machines: Physical properties characterization

Early structural damage and resulting failures can be caused by vibration in AC electrical machines. Since the stator is under a magnetic field that varies with time, the stator magnetic material contracts and expands due to the magnetostriction, producing noise and vibration. Therefore, a low magnetostriction value is desirable to minimize the effect of vibration and avoid earlier motor breakdowns. However, not only a low magnetostriction value is enough. Low values of magnetic losses avoid the material heating, consequently preventing magnetic properties degradation. To minimize these magnetic losses, a suitable material might have high resistivity and magnetic permeability, and also low coercive field. Fe-Ti alloys have low magnetostriction values and are soft magnetic material, making them good candidates for using in motors' stators. In the present work, two Fe-Ti alloys with composition 6.9 wt% Ti (8 at.%) were studied. One of the alloys was studied after the as cast ingot annealing at 1200 degrees C. The other alloy was hot rolled from 7 mm down to 0.5 mm of thickness. The maximum magnetic induction of the rolled alloy was 1.74 T, about 12% higher than the not rolled one. In addition, the rolled Fe-Ti alloy magnetostriction is lower than 1 ppm up to 1.25 T, while in the not rolled condition is also 1 ppm, but only up to 0.75 T.