Decreasing the W-Cr solid solution decomposition rate: Theory, modelling and experimental verification

Abstract

Tungsten-based alloys are essential materials in the nuclear fusion reactors’ development. Particularly, tungsten-chromium single solid solution is interesting for the combination of a good oxidation behaviour and lack of lower-melting-point phases. The W-Cr system has a miscibility gap though and the solid solution within the particular condition is inherently metastable/unstable and tends to decompose forming a Cr-rich phase. In this study, we have combined computer simulations and experimental work to find additional alloying elements to promote the stability of W-Cr solid solution. The results showed that alloying with Ta may result in lowering the stabilising temperature of the alloy, positively affecting the decomposition rate. Experiments performed on a W-Cr-Ta alloy showed prolonged solid solution lifetime when compared to W-Cr alloy. Formation of the third decomposed phase, enriched in Ta, was observed and changes in the chromium diffusion in the alloy were identified to be the governing factor for slowing down the decomposition.