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测定了GH4738合金在650、700、750及800℃空气环境下的疲劳裂纹扩展速率da/d N-ΔK曲线及疲劳裂纹扩展寿命a-N曲线,得出了温度对合金疲劳裂纹扩展的影响规律,并结合组织性能、疲劳特征、高温及室温下晶界氧化情况等分析了温度对合金疲劳裂纹扩展的影响。结果表明,随着温度升高,GH4738合金的疲劳裂纹扩展速率(FCGR)增加,合金的断裂方式由沿晶和穿晶混合型断裂向完全沿晶断裂转变;在初始应力强度因子幅度DK为40 MPa·m1/2、晶粒尺寸为30~40 mm时,合金的疲劳裂纹扩展寿命在650~700℃内显著下降,存在一个温度敏感区间,其原因并不是材料的组织和力学性能的变化,主要是高温下的氧化作用所致;O通过裂纹尖端、滑移带间接进入晶界或O直接渗入晶界的方式,与晶界处的活性元素Co、Ti、Al反应生成脆性氧化物,从而降低了晶界强度,使合金的抗疲劳性能显著下降。
The fatigue crack growth rate da / d N-ΔK curve and fatigue crack growth life aN curve of GH4738 alloy were measured in the air environment of 650, 700, 750 and 800 ℃. The influence of temperature on the fatigue crack growth was obtained. The effect of temperature on the fatigue crack growth was analyzed based on microstructure and mechanical properties, fatigue characteristics, high temperature and grain boundary oxidation at room temperature. The results show that as the temperature increases, the fatigue crack growth rate (FCGR) of GH4738 alloy increases, and the fracture mode changes from intergranular and transgranular mixed fracture to complete intergranular fracture. When the initial stress intensity factor (DK) is 40 MPa · m1 / 2. When the grain size is 30 ~ 40 mm, the fatigue crack propagation life of the alloy decreases significantly from 650 ℃ to 700 ℃, and there is a temperature-sensitive zone. The reason is not the change of the microstructure and mechanical properties of the alloy. Mainly due to oxidation under high temperature; O through the crack tip, slip band indirectly into the grain boundary or O directly penetrate the grain boundary, and the grain boundary active elements Co, Ti, Al react to form brittle oxides, which Reduce the grain boundary strength, the anti-fatigue properties of the alloy significantly decreased.