一种单晶高温合金不同温度的高周疲劳性能

研究了一种单晶高温合金700℃和800℃的高周疲劳性能,采用扫描电镜和透射电镜分析了断口和断裂机制.结果表明,随着温度升高,合金的疲劳强度系数降低,Basquin系数增加,高周疲劳极限降低.合金700℃与800℃具有相同的高周疲劳断口,都有几个{111}面平面组成,为类解理断裂机制.疲劳断口由裂纹源区、扩展区和瞬断区3部分组成.裂纹起源于试样的表面或亚表面,并沿{111}面扩展.扩展区可见河流状花样、滑移带、疲劳弧线和疲劳条带特征.瞬断区可见解理台阶和撕裂棱.断裂后γ′相仍保持立方形状,位错不均匀分布在γ基体通道中.

High cycle fatigue properties of a single crystal superalloy at different temperatures

The high cycle fatigue properties of a single crystal superalloy were investigated at 700 ℃ and 800 ℃. SEM and TEM were used to study the fracture surface and fracture mechanism. The results showed that the fatigue strength coefficient dropped, Basquin exponent rose and the fatigue limit decreased with the increasing test temperature. The fracture surfaces were the same at the above temperatures, each consisting of several {111} planes. The fracture mechanism was all quasi-cleavage fracture. Fatigue source zone, crack propagation zone and transient fracture zone could be seen on the fracture surface. The fatigue crack initiated at or near the surface and propagated along {111} planes. The river pattern, slip band, fatigue arc and fatigue striation could be seen in the crack propagation zone. The cleavage step and tear ridge could be seen in the transient fracture zone. The γ′ phase morphology still maintained cubic after fracture. Dislocations were unevenly distributed in the γ matrix of the alloy.