Fatigue Behavior of LPBF GRCop-42 Specimens with Cooling Channels

The increasing use of additive manufacturing technologies such as Laser Powder Bed Fusion (LPBF) has enabled the manufacturing of parts with complex features such as optimized cooling channels. However, due to the layer-by-layer deposition of LPBF requiring an approximation of design intent, cooling channels manufactured by LPBF are affected by surface roughness effects and manufacturing inaccuracies. Consequently, the effect of implementing them on the mechanical properties of parts should be studied to understand their limits of applicability. This study aims to determine the effect of helical cooling channels in LPBF GRCop-42 specimens on their high-cycle fatigue properties. We present monotonic tensile testing and high-cycle fatigue testing results for three specimen types (no channel, straight channel and helical channel) of LPBF GRCop-42 under uniaxial loading, tested at two temperature conditions (room and 500°C). We show that at room temperature, the no channel specimens had the highest fatigue strength, followed by the straight channel and then helical channel specimens. The relative significance of potential causes for the detriment in fatigue life for the straight and helical channeled specimens were quantified using finite element analysis (FEA) and analytical fatigue models (based on Murakami-type defect corrections), and the findings from this analysis were validated by experimental observations from fracture surface analysis. Our results demonstrate that for the straight channel specimens, manufacturing-induced porosity around the channel is relatively a stronger driver for the detriment of fatigue life, compared to surface roughness. For the helical channel specimens, intended to simulate complex cooling channels in real-world applications, the effects of surface roughness combined with multiaxial stress concentrations around the channel were the primary driver for the lesser fatigue life. We anticipate our results will be useful for designers and manufacturers of LPBF components with complex features, and those involved in the potential implementation of LPBF GRCop-42 parts in high-cycle fatigue applications.