Si enrichment of conventional electrical steel by PVD for high frequency applications.

The present work deals with the viability of a method for Si enrichment of conventional Fe-3%Si sheets, by means of physical vapour deposition of Si a t its surface and subsequent diffusion heating. The aim is to obtain magnet ic sheets with a Si content of 6.5wt%, for they show higher resistivity and null magnetostriction, leading to lower energy losses and solving the nois e problems at high frequencies. The PVD deposited films, with similar to 5 mu m thickness, show good adhesi on to the substrate. Concerning the heat treatment, there is a critical hea ting rate between 5 and 15 degrees/min, above which delamination of the fil m is observed without formation of intermetallics at the interface. At 3 de grees/min the conditions for the formation of intermetallics are given. Dir ect heating up to 800 degrees C leads to the formation of a Fe3Si(alpha(1)) surface layer, which, being brittle, does not delaminate during the heatin g process. Subsequent heating up to temperatures around 1200 degrees C allo ws the homogenisation of the sheet composition. There is evidence of Kirken dall effect in the diffusion couple Fe3Si(alpha(1))/Fe(alpha), due to the f act that the diffusion of Fe in Fe3Si(alpha(1)) is faster than the diffusio n of Si in Fe(alpha).