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 250μm 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 250μm. A linear relationship between the small crack growth rate and crack length can be found when plotted on double-logarithmic coordinate.