Experimental investigation of phase equilibria in the Co−Hf−Mo system at 1373 and 1223 K

Abstract Spark plasma sintering (SPS) was used to fabricate the Co−Hf−Mo−Ni diffusion multiple in a designed geometry to contain two Co−Hf−Mo and Co−Hf−Ni diffusion triples in one sample, which offers a high-efficiency and low-cost method for preparing this diffusion multiple. In this work, the phase equilibria of the Co−Hf−Mo system at 1373 and 1223 K were established according to the analysis of results obtained using a scanning electron microscope (SEM), X-ray diffraction (XRD), and electron probe microanalysis (EPMA) from annealed diffusion triples and equilibrated alloys. The homogeneity range of the ternary compound τ with Hf9Mo4Co structure was verified in diffusion triples, and solubilities of Mo in Co−Hf, Co in Mo−Hf, and Hf in Co−Mo binary compounds were detected at 1373 and 1223 K. The isothermal sections over the entire composition range at 1373 and 1223 K were successfully constructed. The obtained phase equilibria data provide guidance for the development of multicomponent γ/γ′ Co-based superalloys