DD98M镍基单晶高温合金900℃高周疲劳行为

HIGH CYCLE FATIGUE BEHAVIOR OF A NICKEL-BASED SINGLE CRYSTAL SUPERALLOY DD98M AT 900℃

研究了无Re第二代单晶高温合金DD98M在900℃时的高周疲劳性能.结果表明:该合金的疲劳寿命随着应力水平的升高而减小,且缺口降低了合金的疲劳强度和疲劳寿命,900℃时光滑和缺口试样的疲劳强度分别为574和360 MPa;利用扫描电镜(SEM)观察疲劳试样的断口形貌,发现缺口试样为多裂纹源断裂,裂纹主要萌生于缺口根部应力集中区域,而光滑试样为单一裂纹源断裂,裂纹源起始于试样表面、次表面疏松处或碳化物处;利用透射电镜(TEM)观察疲劳变形后的位错组态,发现光滑试样中主要以基体通道中的位错滑移为主,高应力水平下会出现位错对切割γ′相,而缺口高周疲劳在高应力下主要变形机制为不全位错切割γ′相形成层错.

High cycle fatigue（HCF） behavior of the second generation single crystal nickel-based superalloy DD98M without Re addition at 900°C was investigated.The results indicate that HCF lifetime is reduced with increase of cyclic stress amplitude.Compared to smooth specimens,the fatigue lifetime and strength of notched specimens are decreased markedly.The fatigue strengths for smooth and notched specimens are 574 MPa and 360 MPa,respectively.Fracture observation by SEM shows that there exist many sites of crack initiation for notched specimens due to stress concentration of the notch,while for smooth specimens,crack generally initiates at pores and inclusions on the surface or subsurface.Deformed microstructures observed by TEM reveal that for smooth specimens,dislocation movement in the matrix is the main deformation mechanism and shearing 7＇ particles by dislocation pairs occurs occasionally under high stress level.In contrast,cutting 7＇ phases by partial dislocations, which formed stacking faults in 7＇,is the dominant deformation mechanism for notched HCF specimens.