Experimental study on phase relations in the Al-Mo-Nb ternary system

Abstract

Aluminium alloying can improve the anti-oxidation property of the Nb/Mo-Si-based superalloy. Therefore, the Al-Mo-Nb ternary system is one of the important subsystems of the Al-alloyed multi-component system. The isothermal sections at 1200 and 1000 ℃ and the liquidus projection of the Al-Mo-Nb system were studied experimentally. The phase structures and the phase constituents of the as-cast alloys and the annealed alloys were analyzed and measured using X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) as well as electron probe micro-analysis (EPMA) techniques. Five three-phase regions and eleven two-phase regions in isothermal section at 1000 °C and six three-phase regions and twelve two-phase regions in isothermal section at 1200 °C were determined, and no ternary compound was observed. Fourteen primary solidification regions and eleven invariant reactions were deduced based on the study on the solidification processes of the as-cast alloys. The present experimental results can be used for the future thermodynamic assessment of the Al-Mo-Nb ternary system, and be helpful for the database development of the multi-components Nb/Mo-Si-based superalloy system.