engleski

Microhardness and Microstructural Changes of Al-W Thin Films during Isochronal Annealing

Thin films of Al-W alloys were prepared on sapphire substrates by magnetron co-sputtering. The results of X-ray diffraction analysis proved that the as-prepared samples, within a composition range Al80W20 to Al67W33, were 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. The thermal stability of films was investigated after isochronal annealing the samples for one hour in a temperature range 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 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 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 Al5 W) co-existing 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. All our microhardness isochronal curves obtained for the both types of annealed samples indicate that mechanisms influencing microhardness change during annealing are similar for amorphous and crystalline states.

Preparation of Al-W thin films by magnetron sputtering; metastable crystalline films; amorphous films; isochronal annealing; X-ray diffraction.

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