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 Microstructures and High Cycle Fatigue Propertiesof the Single Crystal Superalloy DD6

摘要:

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℃/1h、1200℃/50MPa/1h二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℃/1h、1200℃/50MPa/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℃/1h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℃/50MPa/1h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℃/1h的超温使合金高周疲劳性能降低，1200℃/50MPa/1h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。

Abstract:

In order to study the effect of the over-temperature on the microstructures and high cycle fatigue properties of DD6 single crystal superalloy, the alloy after standard heat treatment was hold at 1200℃ and 1200℃/50MPa for 1h respectively, which simulated different over-temperature process, and was then air cooled. The microstructures and high cycle fatigue properties of DD6 alloy with standard heat treatment, 1200℃/1h, 1200℃/50MPa/1h at 800℃ were investigated by SEM and rotary benging fatigue testing machine. The results show that after heat-treatment at 1200℃ for 1h, the size of γ′ particles becomes larger slightly and quite nonuniform, serrated γ/γ′ interface appeares and a small number of fine secondary γ′-particles precipitate in the γ matrix channels. After heat-treatment at 1200℃/50MPa for 1h, the size of γ′ particles also becomes larger while also quite nonuniform; a large number of fine secondary γ′ particles precipitate in the γ matrix channels which have become wider significantly and the directional coarsening of γ′ 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 that of the alloy by 1200℃/1h, but are similar to the alloy by 1200℃/50MPa/1h. Analysis on fracture surfaces of three heat treatment process at 800℃ demonstrates that quasi-cleavage mode is observed.