Coating of Additively Manufactured 316LStructures & Coverage in Complex Geometries : Investigating Roughness Parameters

Sammanfattning

Additive manufacturing by Laser Powder Bed Fusion (LPBF) makes it possible toproduce 316L stainless steel parts with complex geometries such as angled surfaces,internal features and lightweight structures. However, LPBF surfaces are oftenrough and contain peaks, valleys, pores and partially melted powder particles. Thesesurface features can affect coating coverage and make it more difficult to protect thematerial properly. This thesis investigated how a ceramic coating covers LPBFmanufactured 316L stainless steel with different printing angles from 50° to 90°.The main focus was to study how surface geometry affects coating coverage and toidentify which roughness features are most critical. Surface roughness was measured using profilometry and evaluated using Ra(arithmetical mean roughness), Rp (maximum profile peak height), Rv (maximumprofile valley depth) and Rsk (skewness of the roughness profile). Cross-sectionalSEM, EDS chemical analysis and Vickers hardness measurements were also used tostudy the coating, microstructure and mechanical response. The results showed thatRa did not clearly describe the coating effect, since coated and uncoated values weregenerally close. Rp showed some changes in peak height but the trend was notconsistent for all angles. The clearest coating effect was observed in Rv where thecoated samples showed less negative values meaning the surface valleys becameshallower after coating. This suggests that the coating interacted mainly withrecessed surface features. SEM showed good apparent contact between the coatingand substrate meanwhile EDS showed coating-related elements near the surface.However, the growth mechanism could not be fully confirmed. Hardness decreasedfrom 225.12 HV3 to 175.34 HV3 after coating due to the annealing process.Overall, the coating was able to cover LPBF 316L surfaces with different geometriesand Rv was the most useful roughness parameter for evaluating the coating effect.