Yttria-Reinforced Fe-Cr Ferritic Alloy-Based Nanocomposites for Fusion Reactor Structural Applications

Ferritic steel with oxide dispersion strengthening is a promising material for fusion and fission reactor components. In the present study, the influence of Mo, V, and Zr on microstructural evolution, thermal stability, and mechanical properties of yttria-dispersed ferritic Fe-14Cr-1Ti-0.25Y2O3-0.3 wt pct X (X = Mo/V/Zr) steels was investigated. This work is inspired by the concept of MA957 alloy, where Mo was replaced by V/Zr to develop new alloy compositions with possible improvement of thermal stability and mechanical properties through grain refinement and oxide dispersion strengthening. These steels were developed by mechanical alloying (MA) and subsequently consolidated by spark plasma sintering (SPS) at different temperatures (900 °C, 1000 °C, and 1050 °C) in high-purity argon atmosphere. The relative sintered density was found to be ~ 97 to 98 pct for specimens spark plasma sintered (SPSed) at 1050 °C. Microstructural analysis of the SPSed specimens (using scanning electron microscopy/transmission electron microscopy-selected area diffraction (SEM/TEM-SAED)) confirmed the formation of uniformly dispersed Y-Ti-O, TiO, and Ti-Cr-O nanosize complex oxide particles within the ultrafine ferritic matrix grains (~ 200 nm). The nanoindentation hardness value is found to correlate well with the compressive strength and wear resistance of the corresponding batches. The influence of V addition in Fe-14Cr-1Ti-0.25Y2O3 alloy is established to yield better thermal stability and superior mechanical properties (nanoindentation hardness of 16.7 GPa, compressive strength of 3068 MPa) as compared to Mo/Zr-stabilized alloys. This was analyzed and discussed in terms of microstructural evolution and strengthening mechanisms involved in comparison to the Mo/Zr-added steels.