疲劳是涡轮叶片的一种主要失效模式.本文开展了DD11单晶合金在650℃中温条件下2种应力集中系数(Kt=1(光滑状态)、Kt=3(缺口状态))的旋转弯曲疲劳性能研究,对比了2种应力集中系数下的疲劳强度,并开展了相关断口分析.结果表明:应力集中系数由Kt=1增大到Kt=3时,疲劳极限由446 MPa降低为311 MPa,说明DD11单晶合金疲劳性能存在应力集中敏感性;疲劳寿命由105提高到107时,光滑状态由600 MPa降低为420 MPa,疲劳强度降低幅度为180 MPa,而缺口状态由370 MPa降低为290 MPa,降低幅度为80 MPa,说明应力集中条件下DD11单晶合金的疲劳寿命对于外载变化较敏感.断口分析表明,光滑试样断口(应力500 MPa/疲劳寿命9.7×105)由几个相交的光滑晶体学平面组成,疲劳源萌生在距表面100μm左右的铸造孔洞;缺口试样断口(应力340 MPa/疲劳寿命8.1×105试样)呈平面状,与应力轴垂直,为多源疲劳模式,疲劳源观察到小刻面,在加工刀痕不连续位置萌生.
The fatigue is one of the important failure modes of turbine blades. Rotating-bending fatigue performance of DD11 single crystal superalloy with two stress-concentration coefficients (SCs) (smooth:Kt=1, Notch:Kt=3) at 650℃ was investigated. Fatigue strengths of two SCs were compared and the fracture morphologies of fatigue were analyzed. The results show that fatigue limit declines from 446 MPa to 311 MPa when SC rises from Kt=1 to Kt=3, indicating that the clear stress concentration sensitivity exists in the fatigue performance of single crystal superalloys. Fatigue strength of smooth statue decreases from 600 MPa to 420 MPa when fatigue cycle increases from 105 to 107 , in which the amplitude of smooth statue is 180 MPa while the one of notched statue is 80 MPa. It indicates that the change of applied load exert a crucial role on the fatigue cycle of DD11 single crystal superalloy. Fatigue fracture surface of the smooth specimens ( stress: 500 MPa/cycle: 9. 7 × 105 ) was composed of several smooth crystallographic plane, initiated by a casting hole 100 μm from the surface, whereasfatigue fracture surface of the notched specimens(stress:340 MPa/cycle:8.1×105) is plane and perpendicular to the applied force axis, which is a multi-source fatigue model. Moreover, the main source initiated as the small facet on the discontinuous machine marks.
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