Comparison of Fatigue Crack Propagation Behavior of Additive-Manufactured Zero Thermal Expansion Alloy with Forged and Casted Materials

This study examined the fatigue crack propagation (FCP) behavior of three kinds of zero thermal expansion (ZTE) alloys. The specimens were manufactured by one of three processes, (casting, forging, and laser additive manufacturing: selective laser melting (SLM)). The FCP rates in the casted alloy were similar to SS400, which was used for comparison. In the SLM product, the FCP rates were higher than the casted alloy and slightly higher than forged alloy, particularly in the low ΔK region. The fracture surfaces were examined by scanning electron microscopy. A rough crack surface was observed in the casted alloy, but small marks along the crack propagation direction were observed in the SLM specimen. The crack opening load was measured to estimate the FCP behavior and consider the effective stress intensity factor range. In an evaluation by the effective stress intensity factor range, the FCP rates of the specimens produced using the three manufacturing processes were similar. Overall, the ZTE alloy manufactured by SLM showed good FCP behavior compared to the forged alloy. The difference in the results between the two products was attributed to the difference in the fracture surface due to the different microstructures.