变形温度与应变速率耦合作用对TWIP效应Ti-15Mo合金力学性能的影响

Coupling effect of deformation temperature and strain rate on mechanical properties in TWIP Ti-15Mo alloy

变形温度和应变速率均影响β型钛合金的力学性能,且其影响均关联塑性变形过程中变形方式的变化。利用TEM,EBSD,SEM,XRD,OM和拉伸试验机研究变形温度和应变速率耦合作用对{332}〈113〉孪生诱发塑性效应Ti-15Mo合金力学性能的影响。结果表明:在298 K和573 K下,屈服强度均随应变速率的增加逐渐升高,即依赖于位错热激活过程,且573 K下显著的位错热激活作用使得屈服强度表现出更大的应变速率依赖性。不同于298 K下,Ti-15Mo合金在573 K下通过{332}〈113〉孪生和位错滑移耦合变形;构建的流变应力模型表明位错强化成为其主要强化方式。高应变速率下,塑性变形早期形成的更多孪晶虽然会抑制孪生的进一步产生降低加工硬化率,但同时有效降低位错不均匀分布引起的局部应力集中延缓颈缩的发生;两个方面的共同作用使得Ti-15Mo合金在变形温度和应变速率耦合作用下呈现出更小的应变速率依赖性。

Both deformation temperature and strain rate affect the mechanical properties ofβtitanium alloy,and are related to the change of deformation mode in the process of plastic deformation.The effects of deformation temperature and strain rate coupling on the mechanical properties of{332}〈113〉twinning induced plastic effect Ti-15 Mo alloy were studied by TEM,EBSD,SEM,XRD,OM and tensile testing machine.The results show that as increase of strain rate,yield strength increases at 298 K and 573 K,which is intensively dependent on dislocation thermal activation behavior.The larger contribution of dislocation activation at 573 K exhibites the higher strain rate dependency on yield strength.At 573 K,the Ti-15 Mo alloy is deformed by{332}〈113〉twinning and dislocation slip,which is different from that at 298 K,and the established flow stress model indicates that dislocation strengthening has a greater contribution.At a high strain rate,the formation of more twins at early deformation suppresses the subsequent formation of twins,decreasing the work hardening rate,whereas can effectively decrease the local stress concentration due to the inhomogeneous distribution of dislocations,delaying the necking.Consequently,these two factors result in the lower strain rate dependency on flow stress in the Ti-15 Mo alloy under the coupling effect of deformation temperature and strain rate.