A Microstructural Study of the Al-Cr-Ru System

Abstract Work undertaken on the Al-Cr-Ru system has shown excellent oxidation resistance in air up to 1500°C for compositions between Al20:Cr60:Ru20 and Al35:Cr32:Ru33 (at.%). Since no phase diagram data for the Al-Cr-Ru system have been published to date, an investigation was initiated. This part of the investigation is to identify the phases which form on solidification, and to derive the liquidus surface for alloys containing in excess of 50 at. % aluminium. Samples were prepared as arc-melted buttons from 99.9% pure elements, and were analysed in the as-cast state in the SEM using EDS with elemental standards, and by X-ray diffraction. The B2 phase, based on AlRu, extends to at least 25 at. % Cr. The Al3Ru2 phase has not been identified, except perhaps as a thin peritectic layer which was too fine to analyse. This is not surprising, since it exhibits very limited extension in other Al- Ru-X ternary systems, and in the Al-Ru binary system reacts peritectically forming AlRU2, and also subsequently decomposes at lower temperatures.