Influence of phase decomposition on mechanical properties and oxidation resistance of WCrY SMART material

Abstract

Self-passivating W-11.4Cr-0.6Y (in wt.%) alloy is a plasma-facing candidate armour material in fusion power plants. In the present work, the as-sintered material, fabricated via ball milling and field-assisted sintering, was annealed at 1000 °C for varying durations to induce phase decomposition. This process leads to the transformation of the initially homogeneous microstructure into two distinct phases: the W-rich phase (αW, Cr) and the Cr-rich phase (αCr, W). Cr-rich phases preferentially form at grain boundaries, where yttrium oxides are also located, and gradually coarsen to the submicron range with increasing annealing time. The chemical compositions of both phases remain relatively stable after 75 h of annealing. The Cr content in (αW, Cr) is 18.6 at.% at 75 h and 17.8 at.% at 100 h. Compared to the as-sintered state, the 100 h-annealed material exhibits significant softening at room temperature and demonstrates increased flexural strength across all tested temperatures, but lower fracture toughness at elevated temperatures. The oxidation behavior of the 100 h-annealed material under humid air at 1000 °C reveals two stages in its TGA curve: inital growth of the inner oxide layer followed by subsequent development of the protecting chromia layer. In contrast, the as-sintered material exhibits a continuous, linear mass increase throughout the oxidation process. These findings present promising prospects of the decomposed microstructure for first wall applications.