Si和Ti对Nb-6Hf-4Zr-2B合金组织和室温力学性能的影响

 为了寻求Nb合金的强度和塑性的平衡，设计了以Nb基固溶体Nbss为主导相的Nb-xSi-6Hf-4Zr-2B-yTi(x=4,8;y=10,30;原子分数)合金，研究了Si和Ti对合金组织和室温力学性能的影响。结果表明，合金由Nbss、Nb3Si和Nb5Si3等3相组成。4Si-(10,30)Ti合金铸态组织是Nb枝晶和分布在枝晶间的硅化物(Nb3Si和Nb5Si3)，8Si-(10,30)Ti合金Nb枝晶间分布的是Nb/硅化物(Nb5Si3)的共晶和Nb3Si，随着Si和Ti含量的增加，硅化物体积分数增加。1 600 ℃退火50 h可使部分Nb3Si共析分解，改变合金的组织形貌和各相的体积分数。随着Si和Ti含量的增加，合金的硬度和强度增加，但塑性和韧性降低。Nb枝晶的失效方式为解理断裂，而硅化物为脆性断裂。

Effect of Si and Ti on Microstructures and Mechanical Properties of Nb-6Hf-4Zr-2B Alloy at Room Temperature

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.