# Wear of 17-4 PH Stainless Steel Patterned Surfaces Fabricated Using Selective Laser Melting
## 2 Materials and Methods  
The design stage for functional surfaces was supported by Rhinoceros 3D computer-aided design software (Version 5.0, Robert McNeel & Associates, Seattle, WA, USA), using a parametric design plugin (Grasshopper). Additively manufactured metallic parts were produced through selective laser melting technology (SLM), which belongs to the family of laser powder bed fusion processes. The ProX DMP 300 manufacturing system was used throughout this study (3D Systems Company, Rock Hill, SC, USA). The main characteristics of the manufacturing system and printing conditions are reported in Table 1.  
Preliminary investigations have been performed to (i) assess the printing system capabilities and deviation from theoretical specifications in manufacturing the desired structures, and (ii) select suitable processing parameters for the textured surfaces. Different kinds of hexagonal structures (Figure 1) have been printed: (i) hexagonal prismatic features, and (ii) hexagonal prismatic features with cylindrical dimples, having a depth equal to the prism half-height (\(h=H/2\)). Each structure has been modelled according to the theoretical minimum feature dimensions allowed by the 3D printer hardware along the x- and y-directions, which are reported in Table 1. Samples having a disk-shaped base with a diameter of 50 mm and thickness of 5 mm were printed directly on the build plate of the machine and the pattern was printed concurrently, on top of the base. The manufactured textures were scaled up to 500% with respect to the starting theoretical minimum size allowed by the 3D printer. The schematics provided in Table 3 show, as an example, the scaled-up Hex structures. Notice that the minimum feature height considered was 200 \(\upmu\)m, corresponding to Scale 1, as 5 times the theoretical layer thickness was found to be a viable starting dimension. In order to perform qualitative and quantitative analysis of the obtained samples, a non-contact computerized numerical control (CNC) measuring system was employed (Quick Vision Apex-QVA by Mitutoyo Corporation, Kawasaki, Japan). The deviations between nominal and actual dimensions, as well as the circularity of cylindrical dimples, were determined using a proprietary software (QVPAK by Mitutoyo Corporation, Kawasaki, Japan). The circularity (roundness) was calculated as the width of the area defined by two concentric circles that bound the data points [21]. It is noted that cylindrical dimples were measured focusing on the bottom surface of the dimples. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Maximum fiber laser power Pmax (W) & 500 \\ Fiber laser wavelength (nm) & 1064 \\ Detail size along axes (\(\upmu\)m) & x = 100, y = 100, z 1 = 40 \\ Laser power (W) & 50\% Pmax \\ Scanning speed (mm/s) & 1200 \\ Hatch spacing (\(\upmu\)m) & 50 \\ Layer thickness (\(\upmu\)m) & 40 \\ Atmosphere & Nitrogen \\ \hline \hline \end{tabular} 1  
\end{table} 
Table 1: Main characteristics of the manufacturing system and printing conditions. Figure 1: Different kinds of hexagonal prism tested for printing (z- is the build direction). Wear tests were carried out, under dry and lubricant-impregnated conditions. A Ball-on-Disk tribometer DTRB 70090 (CSM Instruments, Peseux, Switzerland) was employed in a standard laboratory environment, using single-way rotary mode and 6 mm-diameter 100 Cr6 (AISI 52100) steel ball counterparts. The sample size was such that it was possible to carry out repeated tests on the same sample by changing the sliding radius.