晶体取向对第四代单晶高温合金DD15高周疲劳性能的影响

在定向炉中分别采用籽晶法制备了001]、011]和111]3种不同取向的第四代单晶高温合金DD15,在800℃研究了不同取向的高周疲劳性能,分析了合金不同取向的显微组织、疲劳断口形貌和疲劳断裂组织。结果表明:在凝固方向横截面上不同取向合金的铸态枝晶和热处理γ′相组织明显不同。合金800℃的高周疲劳性能存在各向异性,疲劳极限按111]、001]、011]取向的顺序降低。不同取向合金的高周疲劳都是沿平面断裂,断裂平面与试样中心应力轴线的角度不同,角度按011]、001]、111]取向的顺序逐渐减小。不同取向高周疲劳断口特征基本相同,可见疲劳源区、疲劳扩展区和瞬断区。疲劳裂纹起源于试样表面或亚表面并沿{111}平面扩展。扩展区上可见河流状花样和疲劳条带。瞬断区可见撕裂棱和解理台阶特征,其断裂机制都为类解理断裂。由于试验温度较低,不同取向疲劳断裂后的γ′相仍保持立方形状。

Effect of Crystal Orientation on High Cycle Fatigue Properties of Fourth Generation Single Crystal Superalloy DD15

The fourth generation single crystal superalloy DD15 with001],011]and111]orientations was cast using seed method in the directionally solidified furnace.The high cycle fatigue properties of the alloy with different orientation were investigated at 800℃.The microstructure,fracture surface and fatigue ruptured microstructure of the alloy with different orientation were studied.The results show that the alloy with different orientation has obviously various ascast dendritic structure and heat treatedγ′phase on the section perpendicular to the solidified direction.The high cycle fatigue properties of alloy at 800℃has anisotropy and fatigue limit of the alloy decreases with the sequence of111],001]and011]orientation.The high cycle fatigue of alloy with different orientation breaks along the plane.The angle between the fracture plane and the stress axis of the sample is different and decreases with the sequence of011],001]and111]orientation.The high cycle fatigue fracture characteristics are basically the same.Fatigue source zone,crack propagation zone and transient fracture zone can be seen on the fracture surface of the alloy with different orientation.The fatigue crack initiated at or near the surface and propagated along{111}planes.The river pattern and fatigue striation can be seen in the crack propagation zone.The cleavage step and tear ridge can be seen in the transient fracture zone.The fracture mechanism is all quasi-cleavage fracture.Theγ′phase morphology still maintained cubic after fracture because of lower test temperature.