Microhardness characterization of Al-W thin films

Thin films of Al-W alloys were prepared on sapphire substrate by the magnetron cosputtering . By X-ray diffraction it was revealed that within a composition range Al80W20 to Al67W33 the films were X-ray amorphous. The increase of tungsten content in the films (Al60W40 and Al50W50) resulted in the appearance in a mixture of two or three metastable crystalline phases. Apparently the mixture of crystalline phases coexisted with a small fraction of amorphous one. Vickers microhardness of the as-prepared films varied from ~11 GPa for completely amorphous up to ~20 GPa for the films consisting of a mixture of phases. The thermal stability of films was investigated after isochronal annealing the samples for 1 h in a temperature range from 293 K to 1273 K. It was revealed that there was slight increase in the microhardness during annealing up to a temperature chosen within interval ~(773 -848) K, and such annealing has a small influence on the XRD patterns. In contrast, the annealing above this temperature interval induced detectable changes in the microhardness and a significant changes in X-ray diffraction patterns. The results of analysis of XRD patterns demonstrated that amorphous thin films do not disintegrate directly into the ordered equilibrium (a-W, Al4W, and Al5W) coexisting phases, but the metastable (a-W(Al), b-W(Al), and Al(W) ) intermediary phases were observed 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 offered, and this explanation is based also on the results of the XRD investigation we performed.