October_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 2 0 1 6 Srinivasan et al. reported a low- er wear rate in PLA-20% carbon with minimum layer thickness of 0.075 mm, grid pattern, and 80% infill density by using pin-on-disc tests [18] . The authors hypothesized that it is due to the bet- ter strength of the densely packed sys- tems. In an ABS system, Salem et al. reported that the tensile strength of ABS decreased from approximately 34 to 27.5 MPa as the PLT is increased from 0.1 to 0.4 mm [27] . Comparatively, Sri- nivasan et al. reported the lowest WR of ABS samples printed at 0.1 mm PLT, compared to 0.2 mm PLT during pin-on- disc testing by self-mating [14] . In this case study, we showed that the tribological performance improved as the PLT was increased when slid- ing against alumina. It is hypothesized that PLA samples printed with high PLT helps in forming effective tribofilms, which decreases the µ mean accompanied with marginal increase in WR. In oth- er words, the tribological behavior of PLA is also governed by the formation of tribofilms, which is dependent on PLT and other parameters as discussed earlier. Additional studies are needed to quantify these effects. Currently, we are studying the effect of PLT on the mechanical performance of PLA-based compositions for a direct correlation with tribological performance. We compared the tribological behavior with PLA filled with Cu, Fe, and bronze particulates. PLA-bronze showed the best performance, where the µ mean varied between approximate- ly 0.45-0.47 in all cases. The WR also decreased marginally from 3.3 x 10 -4 to 2.7 x 10 -4 mm 3 /Nm as the PLT was in- creased from 0.1 mm to 0.4 mm (Fig. 4). The µ vs. distance profile was also sta- ble in the PLA-bronze/alumina tribo- couple compared to the PLA/alumina tribocouple (Figs. 3a and b). Figures 5d and 5e show the PLA- bronze surface where signs of abrasive wear and triboxidation (Triboconstit- uent A, Table 2) was observed. Com- paratively, PLA and bronze smeared on the alumina surface to form trans- fer films due to wear of the PLA- bronze surface. This also resulted in triboxidation of bronze constituents (a) (b) (c) (d) (e) (f) Fig. 2 — BSE SEMmicrographs of polished cross section of: (a) PLA-bronze, (b) SE image of PLA- bronze (higher magnification), (c) PLA-Cu, (d) SE image of PLA-Cu (higher magnification), (e) PLA-Fe, and (f) SE image of PLA-Fe (higher magnification) after printing by PLT of 0.2 mm. Inset of (a), (c), and (e ) show the optical micrographs of filaments of PLA-bronze, PLA-Cu, and PLA-Fe, respectively. Fig. 3 — Plot of friction vs. distance of (a) PLA, (b) PLA-bronze, (c) PLA-Cu, and (d) PLA-Fe blocks during sliding against alumina. (a) (c) (b) (d)