Rolling contact fatigue crack propagation relative to anisotropies in additive manufactured Inconel 625

Abstract

Additive manufacturing is steadily gaining acceptance in certain industry segments as a process for the manufacturing of dense metallic components. The Ni-based superalloys belonging to the Inconel family have for many years been in focus for AM research and AM produced components are now becoming commercially available. However, it is still unclear how the microstructural anisotropy, inherent to most AM materials, affects the material performance in a given application. The anisotropy may e.g. influence the mechanical properties and the performance in certain tribological situations, such as when subjected to rolling contact fatigue. Like most AM methods, the powder bed fusion – laser beam process gives the produced components a relatively rough surface. To perform well in demanding tribological situations, the components are commonly machined to a smooth finish.In this work, Inconel 625 produced using PBF-LB is evaluated in a rolling contact fatigue test. Test cylinders (Ø10 mm) have been produced using different build directions and scan strategies, resulting in varying microstructures and textures.In the rolling contact fatigue test, a cylindrical sample is mounted between two Ø 140 mm metal rollers, pulled together via a spring. After testing, the contact tracks are studied using SEM and EBSD to reveal cracks. Cracks were analysed with respect to the microstructure and anisotropies.It was found that the anisotropy influences both the nucleation and growth of cracks. The AM produced specimens were also found to be more prone to transgranular cracking than conventional Inconel 625, which predominantly displayed intergranular cracks.