# Wear Effect on the Contact between a Metallic Pin and a Rotating Polymeric Specim
## 2 Materials and Methods  
### Materials Production  
The pin used for the wear tests was manufactured by an EBM apparatus, Arcam Q10 (Molndal, Sweden), and fed with Arcam AB powder of the Ti6 Al4V ELI-Grade 23 alloy with a particle size ranging from 45 to 100 \(\upmu\)m. This grade is characterized by a reduced content of interstitial elements and iron (Table 1), which makes the alloy more ductile and tough than the more common Grade 5.  
For the printing parameters, such as powder preheating (650 \({}^{\circ}\)C), acceleration voltage (60 kV), beam current (15 mA), scanning speed (4500 mm/s), scan spacing (200 \(\upmu\)m), and layer thickness (50 \(\upmu\)m) refer to what is reported in [20].  
The working parameters were set by the Arcam company to limit the formation of flaws (porosity, unfused powder, or surface roughness [24; 25]) that affect mechanical properties.  
An image of the pin is shown in Figure 1, where the principal geometric parameters are quoted. The plane \(xy\) represents the position of the deposited layers, while \(z\) is the growing direction. The pin is provided with a round tip with a radius of connection equal to 4 mm. No polishing treatment was performed on the tip surface after the EBM process.  
At room temperature, the pin microstructure is lamellar, a type of basket weave, with a greater vanadium content in the interlamellar zone, which consequently results in phase \(\beta\), while the central zone of the lamellas is in phase \(\alpha\)[26]. For metallography and results of the EDX analysis, see [20]. The hardness of the metallic pin is equal to 320 HV, much greater than that of the polymer. Therefore, it does not undergo significant wear phenomena during the pin-on-disc test.  
The polymeric specimens were produced in the form of square sheets with 20 mm sides and 2 mm thickness, obtained by thermoforming the medical grade GUR1020-UHMWPE  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Al** & **V** & **C** & **Fe** & **O** & **N** & **H** & **Ti** \\ \hline \multicolumn{8}{c}{Composition of the powder} \\
6.0 & 4.0 & 0.03 & 0.1 & 0.1 & 0.001 & \textless{}0.003 & Bal. \\ \hline \multicolumn{8}{c}{Range and limits of composition of the alloy Ti6 Al4V ELI–Grade 23 according to ASTM F136} \\
5.5-6.5 & 3.5-4.5 & \textless{}0.08 & \textless{}0.25 & \textless{}0.13 & \textless{}0.05 & \textless{}0.012 & Bal. \\ \hline \end{tabular}
\end{table}
Table 1: Powder composition and range of variation of Ti6 Al4V ELI-Grade 23 alloy (weight %).  
Figure 1: Pin with round tip (sizes expressed in mm).  
powder (average molecular weight of 2-4 \(\times\) 10\({}^{6}\) g/mol, density 0.93 g/cm\({}^{3}\) without calcium stearate) provided by Celanese Corporation, Irving, TX, USA. The process parameters were set according to [PERSON] et al. (2017): temperature 200 \({}^{\circ}\)C and pressure increasing from 1 to 200 atm (1 min. at 0 bar, 1 min. at 50 bar, 1 min. at 100 bar, 1 min. at 150 bar, and 16 min. at 200 bar ([PERSON] et al., 2018)). The plates surrounding the polymer mold for thermoforming were made of steel. The mold cavity has a size of 40 \(\times\) 40 mm\({}^{2}\), and a thickness of 2 mm, to obtain 4 specimens of size 20 \(\times\) 20 mm\({}^{2}\), with a thickness of 2 mm by simple manual cutting. To facilitate the release of the polymer from the mold, a sheet of Teflon(r) with a thickness of 0.1 mm was interposed both above and below the cavity.