Microhardness characterization of Al-W thin films

Thin films of Al-W alloys were prepared on sapphire substrates by magnetron co-sputtering. By X-ray diffraction, it was revealed that, within a compos ition range Al80W20 to Al67W33, the films were amorphous. The increase of t ungsten content in the films (Al60W40 and Al50W50) resulted in the appearan ce in a mixture of two or three metastable crystalline phases. Apparently, the mixture of crystalline phases co-existed with a small fraction of an am orphous one. Vickers microhardness of the as-prepared films varied from sim ilar to 11 GPa for completely amorphous up to similar to 20 GPa for the fil ms consisting of a mixture of phases. The thermal stability of films was in vestigated after isochronal annealing the samples for Ih in a temperature r ange from 293 to 1273 K. It was revealed that there was slight increase in the microhardness during annealing up to a temperature chosen within the in terval similar to 773-848 K, and such annealing has a small influence on th e XRD patterns. In contrast, the annealing above this temperature interval induced detectable changes in the microhardness and significant changes in X-ray diffraction patterns. The results of analysis of XRD patterns demonst rated that amorphous thin films do not disintegrate directly into the order ed equilibrium (alpha -W, Al4W, and Al5W) co-existing phases, but the metas table (alpha -W(Al), beta -W(Al), and Al(W) intermediary phases were observ ed to appear in the films before the former phases were observed. Thus, for the microhardess behaviour during isochronal annealing of Al-W thin films an explanation given for the metallic glasses investigated earlier can be o ffered, and this explanation is based also on the results of the XRD invest igation we performed. (C) 2001 Elsevier Science Ltd. All rights reserved.