Effect of Different Sizes of α Phase on Tensile Properties of Metastable β Titanium Alloy Ti-5.5Cr-5Al-4Mo-3Nb-2Zr

不同尺寸的α相对亚稳β钛合金Ti-5.5Cr-5Al-4Mo-3Nb-2Zr拉伸性能的影响

To study the relationship between the microstructure and tensile properties of the novel metastable β titanium alloy Ti-5.5Cr-5Al-4Mo-3Nb-2Zr,a heat treatment process of ABFCA(solid solution in α+βregion with subsequent furnace cooling followed by aging treatment finally)was designed,by which α phases of different sizes can be precipitated in the β matrix.The results show that the microstructure obtained by this heat treatment process is composed of primary α(α_(p))phase,submicro rod-like α(α_(r))phase and secondary α(α_(s))phase.The alloy with multi-scale α phase has an excellent balance between strength and ductility.The elongation is about 18.3% at the ultimate tensile strength of 1125.4 MPa.The relationship between the strength of the alloy and the α phase was established.The strength of the alloy is proportional to the power of‒1/2 of the average spacing and width of α phase.The α_(s) phase with a smaller size and phase spacing can greatly improve the strength of the alloy by hindering dislocation slip.The transmission electron microscope analysis shows that there is a large amount of dislocation accumulation at the α/β interfaces,and many deformation twins are found in the α_(p) phase after tensile deformation.When the dislocation slip is hindered,twins occur at the stress concentration location,and twins can initiate some dislocations that are difficult to slip.Meanwhile,the plastic strain is distributed uniformly among the α_(p),α_(r),α_(s) phases and β matrix,thereby enhancing the ductility of the alloy.

为了研究新型亚稳β钛合金Ti-5.5Cr-5Al-4Mo-3Nb-2Zr的微观组织与拉伸性能之间的关系,设计了一种可以在β基体中析出不同尺寸α相的ABFCA热处理工艺(在α+β相区进行固溶处理,然后随炉冷却,最后进行时效处理)。这种热处理工艺获得的微观组织由初生α相(α_(p))、亚微米级棒状α相(α_(r))和次生α相(α_(s))组成。结果表明,具有多尺寸α相的合金具有较高的强度和极好的塑性。当合金的极限抗拉伸强度为1125.4 MPa时,合金的断后伸长率可以达到18.3%。建立了合金强度与α相之间的关系,即合金的强度与α相的宽度以及平均间距的-1/2次幂成线性关系,尺寸和相间距较小的α_s相通过对位错滑移的阻碍作用使合金的强度大大提高。透射电子显微镜观察表明,在α/β界面上存在大量的位错塞积,而且在拉伸变形之后的α_(p)相内发现了大量的形变孪晶。当位错滑移受到阻碍时,在应力集中处萌发孪晶,而孪晶又可以启动一些难以滑移的位错,同时塑性应变在α_(p)、α_(r)、α_(s)相和β基体中均匀分布,使得合金的塑性有较大提升。