Adhesion of HVOF Sprayed WC-Co Coatings on Additively Processed 316L

Stainless steel 316L is among the most investigated material for Selective Laser Melting (SLM), as it is used in a broad range of applications. The surface integrity of SLM parts can be improved with adapted process parameters, however, it usually differentiates from conventional manufacturing techniques. With regard to a subsequent coating process by means of thermal spraying, both the surface topography and the residual stress state of the SLM part have a fundamental impact on the resulting coating adhesion.

In the present work, additively manufactured 316L specimens served as substrates for the ensuing coating deposition by means of High Velocity Oxy-Fuel (HVOF) spraying. Prior to the coating deposition, the SLM parts were exposed to various mechanical post-treatments. The SLM parts were investigated in their initial state as well as under post-treated conditions determining the resulting surface roughness and residual stresses. WC-Co hard coatings were applied onto the SLM parts, using a HVOF spraying process. Vickers interfacial indentation tests were conducted to assess the bond strength of the coating to the SLM substrate. To differentiate between topographical effects and residual stress related phenomena, a stress-relief heat treatment of the SLM parts served as reference state throughout the investigations.