Effects of Ni, Co, B, and Ge on the microstructures and mechanical properties of Nb-Ti-Si ternary alloys

Nb-Si in situ composites with a nominal composition of Nb-22Ti-12Si-X (at.%, X represents Ni, Co, B, or Ge) are prepared using non-consumable arc melting technology. The effects of the alloying elements on the microstructures and mechanical properties are investigated. The Nb-22Ti-12Si ternary alloy consists of Nbss and Nb₃Si. A new phase of Ti₂Ni or Ti₂Co is introduced into the ternary system after adding Ni or Co. The addition of 6% Ge promotes the formation of Nb₅Si₃ and creates significantly finer microstructures. The values of the high temperature strength and room temperature fracture toughness of Nb-22Ti-12Si-6Ge are 566.33MPa and 12.81 MPa·m^1/2, respectively, which are approximately 88.2% and 18.5% higher than those of Nb-22Ti-12Si (300.98 MPa and 10.81 MPa·m^1/2). The addition of 3% B changed the morphological features and induced the appearance of large fine rosettes, which is favorable for restraining the crack propagation, and it also leads to a 22.3% increase in room temperature fracture toughness compared with the Nb-22Ti-12Si ternary alloy.