反应堆耐压壳体用Ti-5Al-3V-3Zr-0.7Cr合金热变形行为研究

ResearchSon the hot deformation behavior of Ti-5Al-3V-3Zr-0.7Cr titanium alloy as a candidate material for pressure hull of fusion reactor

摘要:

利用Gleeble-3800型热模拟试验机对经过三次真空自耗熔炼的Ti-5Al-3V-3Zr-0.7Cr(wt%)合金进行热模拟等温压缩试验,研究了在750~900℃及0.001~1s_-1应变速率下的高温流变行为及再结晶行为。结果表明,在合金的高温变形过程中,流变曲线呈现出明显的先硬化后软化的流变行为特征,应变速率的降低或温度的升高都会使合金的流动应力降低；造成该合金流变软化的主要原因是动态再结晶。动态再结晶的临界应变与峰值应变之间成线性关系,随着温度和真应变增加,再结晶体积分数呈“S”型增加；应变速率减小,再结晶体积分数也呈抛物线增长。合金的最佳高温塑形变形参数为：750℃/0.001-0.01s_-1和850-900℃/ 0.01-0.1s_-1。

Abstract:

_{Ti-5Al-3V-3Zr-0.7Cr titanium alloy, a new near α titanium alloy, as a candidate material for pressure hull of fusion reactor was researched detailedly in this paper. Firstly, the flow behavior was analyzed by stress-st rain curves obtained by isothermal compression of Ti-5Al-3V-3Zr-0.7Cr alloy, and it was found that the stress decreased with the increasing deformation temperature and the decreasing strain rate, the extent of softeningfirstincreasedthendecreased after 800℃with increasing deformation temperature at higher strain rates of 0.1 and 1s-1, while it decreased continuously with increasing deformation temperature at lower strain rates of 0.001 and 0.01s-1, and the flow stress dropped rapidly after peak stress presenting the dynamic recrystallization characteristics. Secondly, the constitutive model of Ti-5Al-3V-3Zr-0.7Cr alloy was developed in the form of the hyperbolicSsine and the deformation activation energy was calculated to be about 548.74 kJ/mol. Thirdly, Based on the conventional recrystallized fraction curves, the evolution of recrystallized volume fraction is greatly affected by the strain rates and the deformation temperature. The flow softening of the alloy has been proved to be mainly attributed to the occurrence of DRX. Based on the dynamic materials model and Prasad’s instability criterion, the power dissipation map and instability map of Ti-5Al-3V-3Zr-0.7Cr alloy were constructed at strains of 0.4 and 0.6, the obtained optimal processing windows of Ti-5Al-3V-3Zr-0.7Cr alloy were 750℃/ 0.001-0.01s-1 and 850-900℃/ 0.01-0.1s-1 with the peak efficiencies of 65% and 73% respectively.}