The benefit of alloying additions of palladium in improving the oxidation resistance of tungsten alloys at elevated temperatures has been reported in this journal recently (1). Now, the enhancement of the high temperature strength of tungsten by alloying with iridium is the subject of a new study at the Arizona State University (2).

The investigators report that dilute alloys containing up to 1 weight per cent iridium in solid solution display considerably enhanced yield and tensile strengths at high temperatures. For a tungsten-0.8 weight per cent iridium alloy, a yield strength improvement of 75 per cent is observed at 1727°C. This gain becomes progressively less marked as the temperature increases towards 2327°C. The incremental strength benefit was found to be linearly dependent on the iridium concentration, consistent with the mechanism of solid solution strengthening by atoms in substitutional positions causing symmetrical lattice distortion. Examination of the fracture behaviour showed that iridium promotes the intergranular failure mode at lower temperatures.

These results demonstrate that iridium is a viable alternative to rhenium as a strengthening alloying element in tungsten. Earlier work by the authors has shown that iridium also improves the fabricability of tungsten at ambient temperatures, and is better than rhenium. Such findings should encourage the use of tungsten-iridium alloys in industrial applications.