Tribological Evaluation Of Additively Manufactured Alumina Ceramics Processed Using Digital Light Processing

Abstract

The current thesis aims to address the lack of wear-response data for additively manufactured technical ceramics in literature, by using digital light processing (DLP) technology to additively manufacture alumina (Al2O3). Parts were first modelled using SolidWorks software, fabricated, and with subsequent thermal treatments, produced dense sintered parts even with 49 vol% solids loading. Firstly, the impact of build orientation and layer thickness in controlling the tribological response were evaluated by printing samples parallel (0°) and perpendicular (90°) to the build plate, and it was found that the samples exhibited distinct surface topographies and near-isotropic thermal responses. Wear mechanisms were found to be a combination of two- and three-body abrasion, adhesive material transfer, and fatigue-induced spallation. Nanoscratch analysis confirmed that the surface containing tribolayer offers mechanical protection approaching that of the polished surface. Then, the above study was complemented by printing samples between 0° and 90° with 15° increments. Wear tests indicated that 45° was the worst performing sample which was rectified by adjusting the layer thickness to match the pixel size of the print strategy of DLP (35 µm) thereby eliminating secondary step structures; this strategy saw an improvement in the counter face wear response as well. Furthermore, designing micro-patterns on the surface proved that staggering, chamfering, having a less-sharp angle seen in hexagonal voids (i.e., 120° as compared to squares with 90° edges) reduced wear, as these patterns trap the tribolayer and wear debris better, which then potentially act as a lubricant, influencing the coefficient of friction. Specially designed wave patterns exploited their geometry and alumina’s hardness to substantially reduce wear, despite the absence of tribolayer formation. Finally, a strengthening mechanism was studied by adding liquid phase forming additives and platelets to induce grain alignment and texture development during sintering. It was found that build orientation highly influenced the templated grain growth, thermal expansion behaviour, and surface morphology. All these modifications helped in understanding the wear response, tribolayer formation, wear mechanisms involved, and orientation dependent anisotropic behaviour of additively manufacture alumina. These findings are novel and are useful in advancing the knowledge of the scientific community.