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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。
The hot deformation compression tests were carried out to study the high-temperature deformation characteristics of TiAl alloy powder at temperature of 1000-1150 ℃ and strain rate of 0.001-1s-1. It was found that the flow stress-strain curve of the alloy possesses stress peaks and rheological softening properties. In order to study the deformation behavior of TiAl alloy under finite strain, a TiAl alloy processing diagram was established based on the dynamic material model (DMM). The experimental results show that at high strain rate (> 0.1s-1) deformation, the material falls into the area of flow instability and surface cracking occurs. This is detrimental to the deformation of the material and should avoid thermal processing in the fluid-prone zone. At the temperature of 1000 ~ 1050 ℃, the strain rate is 0.001 ~ 0.01s-1, the power dissipation rate η is between 35% ~ 50%. The corresponding deformation mechanism in this area is dynamic recrystallization, suitable for hot working. At high temperature (≥1100 ℃) and low strain rate (0.001s-1) deformation, the power dissipation rate η reaches a maximum value of 60%, at which point the material undergoes superplastic deformation.