超温对DD6单晶高温合金组织及高周疲劳性能影响

Effect of Over-Temperature on Microstructure and High Cycle Fatigue Properties of DD6 Single Crystal Superalloy

为了研究超温对DD6单晶高温合金组织及高周疲劳性能的影响,对标准热处理的DD6合金进行1200℃/1 h、1200℃/50 MPa/1 h 2种条件高温短时热处理以模拟超温过程。采用SEM观察标准热处理、1200℃/1 h、1200℃/50 MPa/1h条件下的合金组织,在旋转弯曲疲劳试验机上测试了上述3种条件合金的高周疲劳性能。结果表明:1200℃/1 h的超温使DD6合金的γ'相尺寸稍微增大,立方化及均匀化程度明显降低,基体通道区域析出少量细小二次γ'相,γ/γ'相界面出现锯齿化现象;1200℃/50 MPa/1 h的超温使DD6合金γ'相尺寸增大,立方化及均化化程度明显降低,基体通道显著变宽,基体通道区域析出大量细小二次γ'相,γ'相产生了轻微的定向粗化;1200℃/1 h的超温使合金高周疲劳性能降低,1200℃/50 MPa/1 h的超温的合金高周疲劳性能与标准热处理合金的相当,合金800℃条件下的疲劳断口呈类解离断裂特征。

In order to study the effect of the over-temperature on the microstructure and high cycle fatigue properties of DD6 single crystal superalloy, the alloy after standard heat treatment was held at 1200℃ and 1200℃/50 MPa for 1 h, which simulated different over-temperature processes, and was then air cooled. The microstructure and high cycle fatigue properties of DD6 alloy with standard heat treatment, 1200 ℃/1 h, 1200 ℃/50 MPa/1 h at 800℃ were investigated by SEM and rotary bending fatigue testing machine, respectively. The results show that after heat-treatment at 1200℃ for 1 h, the γ＇ particles become larger slightly in size and quite nonuniform, serrated y/y＇ interface appears and a small number of fine secondary γ＇-particles precipitate in the y matrix channels. After heat-treatment at 1200 ℃/50 MPa for 1 h, the γ＇ particles also become larger in size while also quite nonuniform; a large number of fine secondary γ＇ particles precipitate in the ）, matrix channels which have become wider significantly and the directional coarsening of）,＇ particles occurs. In addition, the rafting of the sheet-like morphology of γ＇ particles is formed along the [100] and [010] directions after fatigue test. The high cycle fatigue properties of DD6 alloy by standard heat treatment are higher than those of the alloy by 1200℃/1 h, but are similar to those of the alloy by 1200℃/50 MPa/1 h. Analysis on fracture surfaces of three heat treatment processes at 800℃ demonstrates that quasi-cleavage mode is observed.