Microstructure Modification of Additively Manufactured Mo–9Si–8B by Annealing and Its Effects on High‐Temperature Mechanical Properties

Electron beam powder bed fusion (EB‐PBF) enables crack‐free Mo–Si–B alloys, yet the effect of postprocess annealing on microstructure and high‐temperature properties is not fully established. Here, EB‐PBF Mo–9Si–8B is annealed at 1200–1600 °C for 1–50 h and characterized by SEM/EBSD, quantitative image analysis, compression, and creep testing. The as‐manufactured state exhibits a very fine Mo ss dendritic network with interdendritic Mo 5 SiB 2 and Mo 3 Si. Annealing at 1200 °C largely preserves this morphology, whereas 1400–1600 °C treatments cause pronounced silicide coarsening. Phase fractions approach the 1600 °C Mo–Si–B equilibrium, and curvature‐driven parabolic growth is found for both intermetallics. Response‐surface modeling defines a practical processing window, where phase balance and morphology are near equilibrium. Compression tests between 1200 and 1400 °C reveal a transition from matrix/subgrain‐boundary‐controlled strength at 1200 °C to intermetallic‐controlled strength at 1400 °C. EB‐PBF Mo–9Si–8B achieves compressive strengths comparable to or above conventionally processed Mo–Si–B alloys. Creep tests at 1093 °C show that annealing at 1600 °C for 50 h reduces steady‐state creep rates partially by up to almost two orders of magnitude, demonstrating the effectiveness of tailored annealing for ultra‐high‐temperature applications.