镍基合金GH4169疲劳小裂纹的扩展行为

基于表面复型法，采用快速固化材料RepliSet监测了镍基合金GH4169单边缺口拉伸试样疲劳小裂纹的萌生和扩展行为，利用光学显微镜对复型进行了观测。结果表明:RepliSet材料可有效复制试样表面形貌，记录疲劳小裂纹的萌生和扩展过程。镍基合金GH4169疲劳小裂纹起始于材料表面夹杂，疲劳小裂纹早期扩展阶段受微观结构影响，扩展速率波动性较大。疲劳小裂纹扩展过程中的临界裂纹长度约为250μm，当主裂纹长度小于250μm时，裂纹扩展非常缓慢；但当裂纹长度超过250μm后，疲劳小裂纹快速扩展成为长裂纹并导致试样断裂。在双对数坐标系中，疲劳小裂纹扩展速率和裂纹长度近似为线性关系。 

Small fatigue crack growth behavior of nickel-based alloy GH4169

On the basis of surface replication method,a fast-curing material named RepliSet was applied to monitor the small fatigue crack initiation and growth behavior of single-edge-notch tension specimens fabricated by nickel-based alloy GH4169.Optical microscope was used to view the replicas.Results showed that the RepliSet material can effectively copy the morphology of specimen surface and record the small fatigue crack initiation and growth process.Small fatigue cracks of nickel-based alloy GH4169 initiated from surface inclusions.The early stage of small fatigue crack growth was influenced strongly by microstructures thus the growth rates had high fluctuations.A critical crack length of about 250 μm existed during the small fatigue crack growth process.The crack lengths increased very slowly when the major crack lengths were shorter than 250μm.However,the major cracks grew rapidly into long cracks and resulted in the final fracture soon after exceeding 250 μm.A linear relationship between the small crack growth rate and crack length can be found when plotted on double-logarithmic coordinate.