Navigating the BCC-B2 refractory alloy space: Stability and thermal processing with Ru-B2 precipitates

TitleNavigating the BCC-B2 refractory alloy space: Stability and thermal processing with Ru-B2 precipitates
Publication TypeJournal Article
Year of Publication2024
AuthorsKube SA, Frey C, McMullin C, Neuman B, Mullin KM, Pollock TM
JournalActa Materialia
KeywordsB2 phase, Calphad, Combinatorial, High temperature materials, Precipitation strengthening, Refractory multi principal element alloys, Thermal processing

Refractory multi-principal element alloys (RMPEAs) could provide next-generation high temperature alloys, but their ductility and high temperature strength need significant improvement. Emulating superalloy γ-γ’ microstructures, RMPEAs combining a ductile BCC matrix with embedded B2 precipitates for strengthening could meet this goal. Two-phase BCC-B2 RMPEAs have recently been demonstrated, but the B2 phase typically exhibits insufficient thermodynamic stability for operating temperatures ≥1300 °C. Using high-throughput CALPHAD predictions, we screen across 3,500 potential BCC-B2 systems. Promising compositions are predicted for alloys combining Ru-based B2s with refractory BCC elements. A total of 20 such compositions were arc-melted to characterize their as-cast and heat-treated microstructures. In these alloys, the RuHf B2 exhibits exceptional stability beyond 1900 °C but cannot be solutionized. By contrast, RuTi does solutionize and reprecipitate between 1300 and 1900 °C, providing a robust thermal processing pathway. RuAl can be solutionized but also tends to form competing intermetallic phases. Altogether, Ru-B2 RMPEAs offer great design flexibility and surpass the stability and thermal processability of previously studied BCC-B2 refractory alloys.