Ti-5.5Al-3Nb-2Zr-1Mo钛合金热变形行为及组织演变规律研究

Study on Hot Deformation Behavior and Microstructure Evolution Rule of Ti-5.5Al-3Nb-2Zr-1Mo Titanium Alloy

为探究Ti-5.5Al-3Nb-2Zr-1Mo钛合金热变形过程中的动态热变形行为及组织演变规律,采用Gleeble-1500热模拟实验机进行了热压缩实验(变形温度855~1015℃、应变速率0.001~10s^(-1)、变形量60%),构建了Arrhenius型热变形本构方程,并对热压缩后的微观组织和晶界结构进行了分析。结果表明:合金在高温热压缩过程中具有明显的动态软化特征,流变应力随变形温度的升高而降低,随变形速率的提高而增大。合金在(α+β)相区的热变形激活能为541kJ/mol,在β相区的热变形激活能为243 kJ/mol。其微观组织演变受变形温度和变形速率影响敏感,合金在(α+β)相区的主要软化机制为动态再结晶,变形晶粒边界处形成了大量细小的再结晶晶粒以及大角度晶界;在β相区软化机制以β相动态回复为主,变形后粗大β晶粒经冷却转变为晶内交错排列的细长针状α相组织。

In order to investigate the hot deformation behavior and microstructure evolution of Ti-5.5Al-3Nb-2Zr-1Mo titanium alloy during hot deformation, the hot compression tests were carried out under the deformation temperatures of 855-1015 ℃, strain rates of 0.001-10s^(-1) and deformation degree of 60% on a Gleeble-1500 thermo-mechanical simulator. The Arrhenius-type constitutive equation of the titanium alloy was constructed. The microstructure and grain boundary character after hot compression were analyzed. The results show that the titanium alloy shows obvious dynamic softening behavior during hot compression, and the peak stress increases with the decrease of the deformation temperature and the increase of the strain rate. The activation energy of hot deformation in the(α+β) two-phase region is calculated as 541 kJ/mol, and the activation energy of hot deformation in the β single-phase region is 243 kJ/mol. The microstructure evolution during hot deformation is sensitive to the deformation temperature and strain rate. During the deformation in the(α+β) phase region, incomplete dynamic recrystallization of the α phase occur, associated with the formation of a large number of high-angle grain boundaries.Meanwhile, the dynamic recovery of β-phase is the main softening mechanism for the alloy during the deformation in βsingle-phase region. An interlaced acicular α metallographic structure appears in the subsequent water quenching process.