Effect of Ta Element on Microstructure and Mechanical Properties of Nb-22Si-20Ti-6Mo Alloy

Abstract:

Nb-22Si-20Ti-6Mo-xTa (x=0, 1, 2, 3, 4, at%) alloys with different contents of Ta were prepared by vacuum non-consumable arc melting method, and effects of Ta content on phase constitution, microstructure and mechanical properties of Nb-22Si-20Ti-6Mo-xTa alloys were investigated. Results show that addition of Ta does not change the phase composition Nb-22Si-20Ti-6Mo-xTa alloys. All alloys consist of Nbss and β-Nb₅Si₃, and Ta is mainly dissolved in Nbss. Microstructure of alloys consists of bulk primary β-Nb₅Si₃ phase and Nbss/β-Nb₅Si₃ eutectic. Addition of Ta refines the microstructure, and the grain size of primary β-Nb₅Si₃ phase decreases from 26.84 μm to 14.65 μm. In addition, the amount of primary phase is decreased with increasing the Ta content, and the amount of eutectic structure is increased. Room-temperature compressive strength of Nb-22Si-20Ti-6Mo-xTa alloys is improved with increasing the Ta content, and it is increased from 2261 MPa to 2321 MPa with increasing the Ta content from 0at% to 4at%. Fracture strain of Nb-22Si-20Ti-6Mo-xTa alloys first decrease and then increase with increasing the Ta content. Fracture strain of NST-0Ta alloy is 9.9%, that of NST-1Ta alloy is 9.7%, and that of NST-4Ta alloy increases to a maximum of 10.6%. Compressive strength improvement of alloys is contributed to solid solution strengthening and grain refinement strengthening by the addition of Ta. Due to refinement of alloy microstructure and the increase in eutectic structure, fracture strain of alloy is increased.