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Inconel pipes that transport cryogenic fluids in rocket engines manufactured by additive manufacturing (AM) were eroded by cavitation. The AM method selective laser melting (SLM) was used to manufacture at lower cost, but had seemingly lower erosion resistance. The cavitation erosion properties of Inconel 625 and 718 are studied as a function of hardness and surface roughness with the ASTM G134 cavitating jet. The samples were studied 3 surface conditions, as deposited/as used in applications, machined and polished, for both forged and AM manufacturing. Indentation reveals slight surface hardening for machined samples. X-ray diffraction (XRD) shows similar polycrystalline γ -Ni-based microstructure for all samples. Scanning electron microscopy (SEM) images of the cut cross-sections reveal the fractures and pits, as well as some porosity in the case of SLM samples. Images of the surfaces during erosion reveal some fracture mechanisms: machined samples erosion start quickly on pits and scratches. The SLM718 samples were found to have good cavitation erosion resistance if machined, while the SLM625 samples have comparatively poorer resistance. As-deposited samples have the lowest resistance, and surprisingly machined samples are more resistant than polished., (© ASM International 2021.)