Ti-20Al-22Nb合金的凝固组织转变及力学行为

Transformation of Solidified Structure and Mechanical Behavior of Ti-20Al-22Nb Alloy

采用熔模铸造方法制备了名义成分为Ti-20Al-22Nb(at%)的合金,分别对铸态、热等静压及退火态合金进行了显微组织及室温拉伸性能分析。结果显示,合金由β基体、针状α2相及少量O相组成。铸态下为粗大的魏氏组织,由于非平衡凝固,原始晶粒内部组织转变不完全,组织中的疏松缺陷及组织不均匀导致合金低的塑性;经过α2+β/B2两相区热等静压消除了疏松缺陷,原始晶粒内部充分析出细小针状的α2相,组织均匀性提高,合金的拉伸延伸率由2%提高到5%;经过α2+/B2+O三相区退火热处理,过饱和β相向平衡态转变,通过包析转变β/B2+α2→O,在针状α2相周围形成环带状O相,合金的延伸率提高到11%。

Ti-20 Al-22 Nb(at%)alloys were prepared by investment casting.The microstructures and tensile properties at room temperature of as-cast,hot isostatic pressed and annealed alloys were analyzed.The results show that solidified alloy consists ofβmatrix,fine acicularα2 phase and a small amount of O phase.The as-cast alloy has course widmanstatten structure.Besides,the phase transformation inside originalβ/B2 grain is incomplete owing to non-equilibrium solidification.Loose defect and inhomogeneity of microstructures cause low plasticity of the material.The loose defects are eliminated by hot isostatic pressing in the two-phase region ofα2+β/B2,acicularα2 phase precipitates fully in the original grains,the microstructure homogeneity improves,and the elongation of the alloy increases from 2%to 5%.After annealing treatment in theα2+/B2+O three-phase region,the supersaturatedβphase transforms to the equilibrium state.Through the peritectoid transformation ofβ/B2+α2→O,ring-shaped O phase forms around needle-shapedα2 phase,and the elongation further increases to 11%.