一种镍基单晶高温合金的反相热机械疲劳行为

采用扫描电镜、透射电镜等方法研究了一种镍基单晶高温合金在600～900℃的反相位热机械疲劳行为,旨在探讨单晶合金的热疲劳变形及断裂机制,丰富单晶合金热机械疲劳理论。试验结果表明:当应变幅由0.6%增大至0.9%时,热机械疲劳寿命下降,塑性应变量和应力范围增大。合金的循环应力响应曲线在低温半周表现为循环硬化行为,而在高温半周则表现为循环软化行为。合金主要的变形特征是局部区域滑移带的运动。热机械疲劳裂纹起始于试样表面应力集中处,并沿着滑移带在{111}面向合金内部扩展,拉应力对合金的断裂起到了主导作用。

On thermo-mechanical fatigue behaviors of a nickel-base single crystal superalloy

The purpose of this paper was to explore the thermal fatigue deformation and fracture mechanism of single crystal alloy and enrich the theory related to it. A nickel-base single crystal superalloy was employed to study OP thermo-mechanical fatigue behavior by using scanning electron microscope (SEM), transmission electron microscope (TEM) and some other research methods. The main results are summarized as follows:A mean tensile stress is observed in OP TMF. With the mechanical amplitude increasing from 0.6% to 0.9%, the fatigue life decreases, whereas the stress range and the plastic strain increase. The cyclic stress response curve of the alloy shows cyclic hardening at half cycle of low temperature while at the high temperature half cycle, the maximum compressive stress decreases during test, indicating a cyclic softening. The main mechanism for OP TMF is the formation of local slip bands in {111} planes. The interaction of creep, oxidation and fatigue damage lead to shorter life for TMF than isothermal fatigue. The fracture and propagation of slip bands is the main fracture style for OP TMF. The tensile stress is dominant factor affecting the fatigue life in the test.