中文摘要：

研究了多功能亚稳β型Ti2448（Ti 24Nb-4zr-8Sn,质量分数,%）合金在β单相区的高温变形行为.结果表明.在低应变速率（≤0.1 s^-）和高应变速率（≥1 s^-1）条件下,真应力和应变速率的双对数关系可以通过2个线性关系分别表征,平均应变速率敏感值（mavg）分别为0.265和0.032,这不同于常规β钛合金随着应变速率的增大而逐渐降低的应变硬化规律,即Sigmoidal曲线特征.微观组织演化和动力学分析显示,这种特殊的双线性关系与高应变速率导致的局域化非均匀塑性变形行为和动态再结晶（DRX）相关联.尽管动态回复（DRV）是该合金高温塑性变形的主要组织演变机制,高应变速率使得组织演变从DRV向DRX转变,并在交错的变形带内形成小于3μm的细晶组织.因此,高应变速率条件下的DRX是实现Ti2448合金高温变形过程中细化组织的主要机制.

英文摘要：

Ti2448 （Ti 24Nb-4Zr-8Sn, mass fraction, %） is a multifunctionalβ-type biomedical titanium alloy with low elastic modulus, high strength and good biocompatibility. The alloy exhibits a peculiar plastic deformation behavior at room temperature called highly localized plastic deformation. With aid of such mechanism, the initial microstructure with coarse grains can be easily refined to homogenous equiaxed microstructure with nano-sized grains by the conventional cold processing such as rolling. In the paper, its high temperature plastic deformation behavior and the corresponding microstructure evolution were investigated in the single β phase field by varying the strain rates in the ranges of 0.001-70 s-1. The results showed that the true stress and strain rate can be described by a bilinear relation, which is in sharp contrast with the conventional Sigmoidal relation found in other β-type titanium alloys. As the strain rates less than 0.1 s-1, the alloy follows the conventionalβ-type titanium alloys with a high average value of strain rate sensitivity being 0.265. As the strain rates higher than 1 s-1, the true stress and strain rate can be described by another linear relation with a much small average value of strain rate sensitivity being 0.032. This is different from other alloys exhibiting gradual decrease of strain hardening with the increase of the strain rates.Microstructure observations and kinetic analyses revealed that such bilinear relation would be related to its highly localized plastic deformation behavior and dynamic recrystallization （DRX）, which are triggered and enhanced at higher strain rates over 1 s-1. Although dynamic recovery （DRV） is still a key microstructure evolution mechanism of the alloy during plastic deformation in single βphase field, the increase of strain rate induces a transformation from DRV to DRX, resulting in significant grain refinement from the initial coarse grains about 80 μm to refined grains less than 3 μm. Thus, the DRX is a crucial mechanism of the T