Wear of 17-4 PH stainless steel patterned surfaces fabricated using selective laser melting

The recent developments in additive manufacturing (AM) are providing unprecedented opportunities in various fields, including the fabrication of advanced materials for tribological applications. The present work describes the results of an exploratory study focused on the analysis of 17-4 PH steel surfaces obtained using selective laser melting (SLM). In particular, the study includes the analysis of baseline (as-produced) and textured steel surfaces. Surface texturing comprises hexagonal prism structures (with or without dimples) arranged in a honeycomb pattern with 50 µm or 100 µm gap spacing. Starting from the minimum printing size enabled by the 3D printing platform, various textures are prepared by scaling up the characteristic dimensions of the prisms up to 500%. The obtained surface patterns are characterized (qualitatively and quantitatively) using a non-contact computerized numerical control (CNC) measuring system. The coefficient of friction (COF) was investigated using a Ball-on-Disk configuration using bearing steel balls as counterparts. For a fixed sliding speed, different contact loads and sliding radii were considered, while the tests were carried out in either dry or lubricant-impregnated conditions. The results of wear tests in both dry and lubricated conditions indicated that the baseline samples are provided with lower COF compared to the textured ones. For the latter, neither the gap spacing nor the presence of dimples led to significant variations in the COF. However, in lubricated conditions, the values of the COF for baseline and textured surfaces were closer and much smaller. In particular, the results provide clear indications regarding reducing the gap between prisms, which had a beneficial effect on the COF in lubricated conditions. Similarly, sensitivity to dimples was quite remarkable, with a reduction in the COF of about 30% when the larger gap spacing between the prisms was used.