Sliding wear characteristics of FDM-processed polylactic-acid in bovine blood serum
Fused deposition modelling (FDM) has so far been recognized for its reliability and simplicity for manufacturing of geometrically-complex polymeric materials with 3D printing technique. Recently, the studies concerning the properties of materials fabricated by using the FDM have been growing, including those related to their wear resistance which is considered of critical when a 3D-printed material must work sliding over the surface of another material during its application. Up to now, however, the influence of several FDM-printing parameters, including the raster orientations, on the wear resistance of the printed polymeric materials have not yet been fully understood. In this research, the influence of raster orientations on the wear resistance of FDM-processed polylactic-acid (PLA) materials in bovine blood serum were determined. A reciprocating pin-on-plate tribometer was used to evaluate wear resistance of a cylindrical PLA pin that slid over the surface of a commercially-pure titanium (Ti) plate. The results showed that the FDM-printed PLA pins with unidirectional raster orientations had higher wear factors (WF), i.e., ~1.5 ´ 10-4 mm N-1 m-1 than those with crossed raster orientations, i.e., ~0.8 ´ 10-4 mm N-1 m-1. Meanwhile, the WF values of Ti surface that slid against PLA pin with crossed raster orientations, i.e., ~0.09 ´ 10-4 mm N-1 m-1, were also significantly lower than those sliding with the pin having unidirectional raster orientation, i.e., 0.34 – 0.41 ´ 10-4 mm N-1 m-1. The result of analysis of the worn surface morphologies shows the indications of surface abrasion, fatigue and polymer film transfer as the possible wear mechanisms of both the FDM-processed PLA pin and its Ti countersurface material. On the basis of all the findings in this research, it can be concluded that the crossed raster orientation is preferable to be used as one of the parameters in printing of the wear resistant PLA rather than the unidirectional raster orientation.
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