Influence of strain rate and temperature on the deformation mechanisms of a fine-grained Ti-6Al-4V alloy
Influence of strain rate and temperature on the deformation mechanisms of a fine-grained Ti-6Al-4V alloy
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DOI：
10.1016/j.msea.2020.139718
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发表时间：
2020-07-14
期刊：
影响因子：
6.4
通讯作者：
Velay, Vincent
中科院分区：
文献类型：
--
作者：
Despax, Laurie;Vidal, Vanessa;Velay, Vincent
根据其初始显微组织，钛合金，如Ti-6Al-4V，在热成形过程中可能具有不同变形机制的激活。在这项工作中，中断拉伸试验和热处理是用来提高细晶Ti-6Al-4V合金在两个温度（750摄氏度和920摄氏度），因此两个不同的β相分数的机械和微观组织行为的理解。通过扫描电子显微镜（SEM）和图像分析确定了显微组织特征，如α晶粒尺寸和相分数。此外，通过电子背散射衍射（EBSD）获得了α颗粒的择优结晶取向以及颗粒之间和内部的局部取向差的演变。通过力学试验，推导出了应变速率敏感性参数和激活能。从所有这些微观结构和力学数据来看，似乎有几种机制取决于应变水平和温度范围而被激活。在750 ℃时，对于高应变速率，变形主要由α相中的位错活动（织构变化、动态再结晶）控制，并且在非常低的应变速率下，可能由GBS控制，GBS与α（回复）和β中的位错活动相适应。相反，在920 ℃时，与高m值相关的整体织构强度的明显降低表明GBS是变形的主导模式。然而，由于在该温度下α/β体积分数约为48%/52%，因此不仅α相而且β相以及α/α和β/β边界可能有助于流动行为。在长变形时间（低应变速率和高温）期间，由体扩散控制的动态粗化行为（进入α和β）可以发生并改变α/β、α/α和β/β边界的类型、分布并减少数量。这可能部分与在920 ℃和10（-4）s（-）（1）下观察到的流动硬化有关。
Depending on their initial microstructure, titanium alloys, as the Ti-6Al-4V may have activation of different deformation mechanisms during hot forming processes. In this work, interrupted tensile tests and heat treatments are used to improve the understanding of the mechanical and microstructural behaviour of a fine-grained Ti-6Al-4V alloy at two temperatures (750 degrees C and 920 degrees C) and so for two different beta phase fractions. The microstructural features like, alpha grain size and phase fraction, were determined by Scanning Electron Microscope (SEM) and image analysis. Moreover, evolution of the preferred crystallographic orientation of alpha grains and local misorientations between and inside grains were obtained by Electron Backscatter Diffraction (EBSD). The strain rate sensitivity parameter as well as the activation energy were deduced from mechanical tests. It appears, from all these microstructural and mechanical data, that several mechanisms are activated depending on the strain level and on the temperature range. At 750 degrees C, for a high strain rate, the deformation is mainly controlled by dislocations activity in the alpha phase (texture changes, dynamic recrystallization) and, at very low strain rate, by probably GBS accommodated with dislocations activity into alpha (recovery) and beta. On the contrary at 920 degrees C, a clear decrease of the overall texture intensity associated with a high m value suggests that GBS is the dominant mode of deformation. Nevertheless, as the alpha/beta volume fraction is around 48 %/52 % at this temperature, not only the alpha phase but also the beta phase as well as alpha/alpha and beta/beta boundaries might contribute to the flow behaviour. During long deformation time (low strain rate and high temperature), dynamic coarsening behaviour (both into alpha and beta), that is controlled by bulk diffusion, can occur and modify the type, the distribution and decrease the number of alpha/beta, alpha/alpha and beta/beta boundaries. This can be partly related to the flow hardening observed at 920 degrees C and 10(-4) s(-)(1).