关键词: 铌合金, 相组成, 微观组织, 材料强度, 断裂韧性

Abstract: To strike a balance between strength and plasticity of niobium alloys, Nb-xSi-6Hf-4Zr-2B-yTi (x=4,8;y=10,30;at%) alloys with an Nbss-dominant microstructure are developed, and the effect of Si and Ti additions on microstructures and mechanical properties of this kind of alloy at room temperature is evaluated. It is found that the alloy contains three phases: Nbss, Nb3Si and Nb5Si3. The microstructures of the as-cast 4Si-(10, 30)Ti alloys are composed of the dendrite Nbss and silicides (Nb3Si and Nb5Si3); as for the as-cast 8Si-(10, 30)Ti alloys, their microstructures are composed of the dendrite Nbss, eutectic (Nbss + Nb5Si3) and silicide Nb3Si. The fraction of silicides goes up with Si and Ti contents increasing. Upon annealed at 1 600 ℃ for 50 h, part of the Nb3Si decomposes into eutectoid and the microstructural morphology and volume fraction of each phase are changed. The hardness and strength enhance with Si and Ti contents increasing, whereas the plasticity and fracture toughness decrease. The fracture mode of the dendrite Nbss is cleavage, while the silicides fracture in a brittle manner.

Key words: niobium alloys, phase composition, microstructure, strength of materials, fracture toughness