Si ENRICHMENT OF CONVENTIONAL ELECTRICAL STEEL BY MEANS OF PHYSICAL VAPOUR DEPOSITION Jon Molina Aldareguia a , Carmen Garcia-Rosales and Javier Gil Sevillano Centro de Estudios e Investigaciones Te ´cnicas de Gipuzkoa (CEIT), Po Manuel Lardizabal, 15, 20009 San Sebastia ´n, Basque Country, Spain (Received March 1, 1999) (Accepted May 19, 1999) Keywords: Soft magnetic material; Magnetic energy losses; PVD; Diffusion Introduction There are several reasons to develop new core materials with higher performance than the conventional Fe -3 wt.% Si alloys. First of all, the energy losses play an important role. Fe-Si alloys are almost exclusively used in applications where magnetization is applied under AC conditions and, therefore, the most important energy losses concerned are Eddy current losses and hysteresis losses (1,2). At the same time, the semiconductor devices are quickly leading towards the use of higher and higher frequencies. Nevertheless, their use in power devices is limited because of the lack of suitable core materials in the transformers to operate at higher frequencies. The high losses and noise problems of conventional Fe -3 wt.% Si alloys at high frequencies limit the magnetisation of such core materials to low levels, preventing the miniaturization of the devices. In this context, Fe -6.5 wt.% Si shows the following advantages (3): firstly, a high resistivity and permeability, and therefore, low Eddy current losses and hysteresis losses, especially at higher frequencies. And secondly, an almost null magnetostriction constant, which allows the noise problems to be solved (4 – 6). However, it is well known that Fe-Si alloys are brittle at silicon contents greater than 4 wt.% Si (7) and therefore, they can not be manufactured by conventional rolling processes. Until now there have been attempts to produce Fe -6.5 wt.% Si by five different routes: new rolling technologies (8 –11), chemical vapour deposition (CVD) from conventional Fe -3 wt.% Si (12–16) strip casting (15), rapid quenching (17) and spray forming (2). From all of them, the one and only method being used on a commercial scale is the CVD route. The aim of this paper is to present the first encouraging results in exploring a new route of producing Fe -6.5%wt. Si: the process of sufficiently enriching a conven- tional Fe -3 wt.% Si thin sheet (0.15– 0.3 mm, non oriented and grain oriented) with silicon by means of PVD and subsequent diffusion heating at high temperatures. a Current address: Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, UK Pergamon Scripta Materialia, Vol. 41, No. 7, pp. 729 –735, 1999 Elsevier Science Ltd Copyright © 1999 Acta Metallurgica Inc. Printed in the USA. All rights reserved. 1359-6462/99/$–see front matter PII S1359-6462(99)00208-0 729