Impact of stereolithography process parameters on microstructure and properties of alumina manufactured parts

Stereolithography is an additive manufacturing process first developed to produce polymer parts and more recently for ceramic parts. This method involves the polymerization, layer by layer, of a ceramic photo-sensitive suspension using laser energy. This results in a green part, with ceramic grains trapped into a polymer matrix, which must be submitted to drying, debinding and sintering. This process being relatively new for ceramics, it is not fully mastered and a lot of phenomena are not understood yet. Many factors, related to the photosensitive system or related to printing parameters and post-processing parameters, influence the quality of the final part (density, mechanical and physical properties, etc.). Research has been carried out on some of these parameters and this bibliographic report aims to give an overview of what has been already done, focusing on alumina parts. First, the densest parts have been obtained thanks to a bimodal powder distribution of alumina in the suspension, by mixing nano and micro sized grains. Then, it has been demonstrated that there is a relation between exposure, which can be modified by changing the speed and the power of the laser, and mechanical properties, since the higher the exposure rate is, the higher the mechanical characteristics (tensile stress at break and Young's modulus) are. Furthermore, hardness and stiffness decrease with the increase of layer thickness but not in a significant way for hardness, while Young’s modulus decreases in a more drastic way, because of the decrease of density. Finally, to use a liquid desiccant for drying is more adapted than an air drying because shrinkage is more homogenous. Regarding debinding, an appropriate two-step debinding (vacuum pyrolysis step followed by pyrolysis in air.) is better than a vacuum pyrolysis which is better than air pyrolysis, since no defects appeared. And for sintering, delamination between layers is greater for relative low sintering temperature and for high sintering temperature, so sintering temperature must be moderately high to obtain the best parts.