含β相TiAl合金高温变形的不连续屈服行为

DISCONTINUOUS YIELDING BEHAVIOR OF β PHASE CONTAINING TiAl ALLOY DURING HIGHTEMPERATURE DEFORMATION PROCESS

在热模拟试验机上进行高温压缩实验,研究了含β相的Ti-42Al-9V-0.3Y合金的高温变形行为,分析了其不连续屈服行为的产生机理.研究表明,含β相的Ti-42Al-9V-0.3Y合金的主要热变形软化机制为β相的动态回复和γ相的动态再结晶,高温变形过程的不连续屈服行为与β相的动态回复和γ相中超位错(Burgers矢量b=1/2(112))的增殖相关.基于Orowan方程建立的位错动力学模型可合理解释该合金不连续屈服的产生原因,证实可动位错密度的快速增加和低的位错速度应力敏感系数m~*容易诱发TiAl合金的不连续屈服.合金在较低温度(1100—1150℃)和较高应变速率(1 s^(-1))下产生波动屈服归因于位错滑移和孪晶交互作用.

γ-TiAl base alloys are promising high-temperature materials for aviation and aerospace applications due to their low density, exceptional high-temperature strength and good oxidation resistance. However, low ductility and poor hot workability limit the use of such alloys. The introduction of β phase appears to be effective to improve the hot workability of TiAl alloys, while the influence of β phase on hot deformation behavior of TiAl alloy has been rarely investigated until now. In this work, high-temperature compression experiments of β phase containing TiAl alloy （Ti-42Al-9V-0.3Y） were conducted on a Gleeble-1500 thermal simulation machine at 1000—1200℃ and strain rates of 0.001—1.0 s-1. The hot deformation behavior of the TiAl alloy was investigated and the discontinuous yielding mechanism was analyzed. The results show that the main deformation softening mechanism was the dynamic recovery （DRV） of β phase and dynamic recrystallization （DRX） of γ phase. The discontinuous yielding behavior was closely related to the DRV in β phase and the multiplication of the superdislocation with Burgers vector $／bm b=1/2〈112〉 in γ phase. The established dislocation dynamics model based on the Orowan equationin the present work could reasonably explain the causes for the discontinuous yielding phenomenon, indicating that the rapid increase of mobile dislocation density and small dislocation motion velocity sensitivity m＊ could induce the discontinuous yielding of the TiAl alloy. In addition, the fluctuating yielding behavior was attributed to the interaction effect of dislocation slip and twin at lower temperatures of 1100—-1150℃ and higher strain rate of 1 s-1.