铸造TiAl基合金的热变形行为及加工图

通过高温压缩模拟试验结果建立TiAl基合金的热加工图,结合扫描电镜、透射电镜等试验手段,研究铸造TiAl基合金在温度为1 000~1 150℃、应变速率为0.001~1 s 1范围内的热变形行为。结果表明:铸造TiAl基合金是温度、应变速率敏感材料,其流变应力随温度升高和应变速率降低而降低。铸造TiAl基合金的高温变形机制以层片晶团的扭折、弯曲及动态再结晶过程为主。在高温(1 150℃),低应变速率(≤0.01 s 1)下变形后,铸态组织中β相含量明显减少直至消除。在变形温度1 150℃、应变速率0.001 s 1下变形时,铸造TiAl基合金未发生超塑性变形;此时由于动态再结晶晶粒异常长大导致加工图上该区域功率耗散值未达到最大,而是有减小的趋势。

Hot deformation behaviors and processing maps of as-cast TiAl based alloy

The hot deformation behaviors of as-cast TiAl based alloy were investigated in the temperature range of 1 000~1 150 ℃ and the strain rate range of 0.001~1 s 1 using isothermal compression modeling tests combining with SEM,TEM,etc.The results show that the as-cast TiAl based alloy is sensitive to deformation temperature and strain rate.Hot deformation mechanisms of this alloy mainly refer to the kinking,bending,and recrystallization of the lamellar colonies.The rheological stress decreases with increasing temperature and decreasing strain rate.Also,the small amount of β phase that exists in as-cast microstructure can be eliminated after deformation at a higher temperature(1 150 ℃) and a lower strain rate(≤0.01 s 1).No superplastic deformation can be found when deformed at 1 150 ℃ and 0.001 s 1;instead,the corresponding power dissipation efficiency η shows the trend of decreasing due to the abnormal growth of dynamic recrystallization grains.