粉末冶金TiAl合金热变形行为及加工图的研究

采用热模拟压缩试验研究了粉末冶金TiAl合金在温度1000～1150℃、应变速率0.001～1s-1范围内的高温变形特性,发现合金的流动应力-应变曲线具有应力峰和流变软化特性。为了研究TiAl合金在有限应变下的变形行为,基于动态材料模型(DMM)建立起了TiAl合金加工图。试验结果表明,在高应变速率(0.1s-1)变形时,材料落入流动失稳区域,出现表面开裂。这对材料的变形是有害的,要避免在流动失稳区进行热加工处理。而在温度为1000～1050℃,应变速率为0.001～0.01s-1时,功率耗散率η值在35%～50%之间。这个区域对应的变形机制为动态再结晶,适合进行热加工。在高温(≥1100℃),低应变速率(0.001s-1)变形时,功率耗散率η达到最大值60%,此时材料发生超塑性变形。

Hot Deformation Behavior and Processing Maps of PM TiAl Alloy

The hot deformation characteristics of PM TiAl alloy were studied in the temperature range of 1000 ～ 1150 ℃ and strain rate range of O. 001 ～ 1s~(-1) using hot compression test. The stress-strain curves exhibited an obvious peak followed by a broad flow sof-tening. In order to investigate the deformation behavior of PM TiAl alloy at a finite strain level, processing maps were constructed on the basis of a dynamic material modeling(DMM). The results showed that the alloy fall into flow instability region due to cracking at higher strain rate (> 0.1s~(-1)). Thermo mechanical processing in this region should be avoided beeanse this was harmful to deforma-tion of the alloy. Power dissipation efficiency ηranged from 35% to 50% in the temperature range of 1000 ～ 1050 ℃ and strain rate range of 0.001～0.01s~(-1). The deformation mechanism of this region was dynamic recrystallization and this region was suitable for thermo mechanical processing. When deformed at higher temperature (≥1100℃ ) and lower strain rate (0.001s~(-1)), power dissipa-tion efficiency ηreached a peak value of 60%. Superplastic deformation occurred in this region.