铸态粗晶Ti-5553钛合金高温变形行为与机理研究

Hot Deformation Behavior and Underlying Mechanism of As-cast Ti-5553 Alloy with Coarse Grain

摘要:

本文借助Gleeble-3800热模拟试验机系统地研究了铸态粗晶Ti-5553合金在温度700 ℃~1100 ℃、应变速率为0.001 s_^-1~10 s_^-1条件下的高温变形行为。研究结果表明合金的流变应力对变形温度和速率都有强敏感性,流变软化过程也随变形参数的改变呈现出不同的模式。通过经典的动力学模型,建立了合金高温变形的本构关系和激活能分布图,进一步基于动态材料模型构建了合金的热加工图并实现了对不同加工区间变形机制的识别。合金在低温区(700 ℃)和高速率区( 1 s_^-1)均展现出失稳变形的特征,包括外部开裂、绝热剪切带、局部流变等机制,在实际加工中应对这些加工区域进行规避。合金在800 ℃及中低速率( 0.1 s_^-1)变形下的主导机制为α相的动态析出,在中高温(900 ℃-1100 ℃)及中低速率变形下的主导机制为动态回复与动态再结晶的结合。此外,合金在高温较低应变速率(1100 ℃/0.01 s_^-1)条件的变形中表现出大范围动态再结晶的行为特点并伴随稳定的流变软化,因此此条件附近的参数区间被认定为该合金的最优加工窗口,应在实际加工中给予优先考虑。

Abstract:

The hot deformation behavior of as-cast Ti-5553 (Ti-5Al-5Mo-5V-3Cr) alloy with coarse grain was investigated at the temperature range of 700 °C-1100 °C and strain rate range of 0.001 s_^-1-10 s_^-1 by Gleeble-3800 thermal physical simulator. The results show that the flow stress is sensitive to both temperature and strain rate, and the flow curves display various softening modes at different conditions. The activation energy map and constitutive relationship are constructed for the alloy, and the average deformation activation energy is calculated as 447.2 kJ/mol. The hot processing map is successfully established based on the dynamic materials model with the identification of underlying mechanisms at various processing regions. Two peak domains are identified in the hot processing map, which are: 800 °C-975 °C/0.001 s_^-1-0.01 s_^-1 and 1000 °C-1100 °C /0.01 s_^-1-0.1 s_^-1, and the flow instability region locates at the region with strain rate higher than 1 s_^-1. External cracking, adiabatic shear banding and/or flow localization are observed at low-temperature deformation and in the flow instability region, and these conditions should be avoided for actual processing. The mechanism at the peak efficiency domains are DRV or the combination of DRV and DRX, among which the region with the occurrence of extensive DRX is recommended as the optimal processing window for the alloy at high temperature about 1100 °C and medium-low strain rate about 0.01 s_^-1.