镍基单晶高温合金DD6热机械疲劳试验

针对单晶气冷涡轮叶片的服役载荷特征,以镍基单晶高温合金DD6为对象,设计开展了薄壁圆管试样热机械疲劳(TMF)试验。结果表明:DD6变形响应呈现出明显的TMF棘轮效应,且与相位角、机械载荷水平等密切相关；在相同载荷条件下,同相(IP)TMF寿命总是明显短于反相(OP)。引入高温保载时间或增大机械载荷均会引起棘轮应变的明显增加,缩短结构寿命。结合断口和纵向切片分析,识别了不同载荷条件下影响单晶寿命的关键损伤因素,其中IP TMF主导损伤机理为蠕变和疲劳,而OP TMF主导损伤机理为氧化和疲劳。 

Experiment on thermomechanical fatigue in nickel based single crystal superalloy DD6

According to the service loads experienced by air cooled single crystal turbine blades, thermomechanical fatigue (TMF) experiments were designed and conducted on thin-walled tube specimens made of nickel based single crystal superalloy DD6. The results indicated that the deformation response of DD6 exhibited remarkable ratcheting effect, which was closely related to the phase angle and mechanical loading; and the lifetime of in phase (IP) TMF under all experiment conditions were shorter than that of out of phase (OP) TMF. Either introducing dwell time at peak temperature or increasing mechanical load led to more ratcheting strains and fewer failure cycles. Based on the metallographic examination on fracture surface and longitudinal section of specimens, the critical life-limiting factors under different load conditions were identified. Creepage and fatigue dominate in the competing damage mechanisms for IP TMF, while oxidation and fatigue dominate for OP TMF.