Influence of phase decomposition on mechanical properties and oxidation resistance of WCrY SMART material
Self-passivating W-11.4Cr-0.6Y (in wt.%) alloy is the plasma-facing armour material candidate in fusion power plants. In the present work, the as-sintered material, fabricated via ball milling and field-assisted sintering, was annealed at 1000℃ 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). Nanosized Cr-rich phases preferentially form at grain boundaries and around yttrium oxides and gradually coarsen with increasing annealing time. The chemical compositions of both phases remain relatively stable after 75 hours of annealing, indicated by the limited peak shift in XRD. The Cr content in (αW, Cr) meassured by EDS is 18.6 at.% at 75 h and 17.8 at.% at 100 h. Compared to the as-sintered state, the 100h-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 100h-annealed material under humid air at 1000℃ reveals two stages in its TGA curve: inital growth of the inner oxide layer followed by subsequent development of the chromia layer. In contrast, the as-sintered material exhibits a continuous, linear mass increase throughout the oxidation process. These findings present prospects of the decomposed microstructure for first wall applications.