气膜孔分布对DD6单晶高温合金高周疲劳断裂行为的影响

Influence of Cooling Holes Distribution on High Cycle Fatigue Fracture Behavior of DD6 Single Crystal Superalloy

利用带不同电液束加工气膜孔分布的DD6单晶气冷叶片模拟试样,研究其在常温下的高周疲劳性能,并对试样断口及断口侧面形貌进行宏观与微观观察。结果表明:在相同的实验条件下,气膜孔的存在对试样高周疲劳寿命的影响较大,无孔试样的平均寿命约为带3排孔试样的4倍,但是气膜孔布局对疲劳寿命的影响相对较小。通过断口宏观与微观观察发现,无孔试样呈线源特征,而1~3排孔试样裂纹均从气膜孔附近起源,呈多源特征。根据断口和晶体学理论推测,对于无孔、1排孔和多排孔试样的中间部位,裂纹沿{001}滑移面扩展;而对于多排孔试样的上下2排孔孔周的裂纹沿{111}滑移面扩展。采用有限元方法分析4种不同试样孔边应力场的分布规律,数值模拟分析结果与试样的断裂位置及形貌吻合。

The modeling air-cooled turbine blades specimens of DD6 single crystal superalloy with different distributions of cooling film holes were used to study the high cycle fatigue properties at room temperature.The SEM fracture observation was carried out.The results indicate that the cooling holes have significant effects on the high fatigue life of DD6 single crystal superalloy.The average life of non-hole specimens is four times of that of the three-row holes specimens under the same testing conditions.However,the distribution of cooling film holes has relatively less influence on fatigue life.The fracture of the specimens with non-hole is linear source by SEM analysis,but the cracks are found around the cooling film holes and the fracture of the specimens with single row to three rows is a typical multi-source rupture,and cracks all initiate from near film holes.According to fracture and crystallography theoretical conjecture,the cracks propagate along the{001}slip plane for non-hole,single-row holes and the middle location of the multi-row holes specimens.However,the cracks around the holes grow along the{111}slip plane for upper and lower holes of the specimens with multi-row holes.In addition,the distribution of stress field along cooling holes of four different specimens was analysed by FEM method.The results show that the fracture location and morphology of specimens are consistent well with numerical simulation analysis.