Abstract: Nb/Nb5Si3 in-situ composites show great potential to replace Ni-based superalloys as a new generation of ultra-high temperature structural materials for aircraft engines. In the present study, Nb/Nb5Si3 in-situ composites with different compositions are prepared by non-consumable arc-melting technology. Constituent phase and microstructure of Nb-Si-Mo ternary alloys are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results indicate that partial liquidus surface projection of Nb-Si-Mo ternary system (<37.5 at% Si) contains four primary phase regions. Two liquid-solid four-phase equilibrium reactions and one solid four-phase equilibrium reaction appear in three-dimensional phase diagram. Between the two liquid-solid four-phase equilibrium surfaces, there exists a three-phase eutectic equilibrium region, the alloys in which solidify into Nbss/β-Nb5Si3lamellar eutectic by L→Nbss+β-Nb5Si3 reaction.

Key words: Nb/Nb5Si3 in-situ composites, Nb-Si-Mo ternary system, phase transitions, liquidus surface projection, three-dimensional phase diagram