Factors affecting strength and shape retention of zirconia micro bending bars during thermal debinding

Abstract

Low-pressure injection moulded (LPIM) zirconia (3Y-TZP) micro bending bars with bending strength up to 2808 MPa were fabricated. It was found that an increase of the surfactant concentration of the processed feedstocks results in an improvement of surface finish and strength of sintered micro bending bars. During thermal debinding, the formation of a binder film on the surface of the micro parts could be observed, which is responsible for the healing of surface defects. Due to high surface-to-volume ratio surface defects determine the fracture behaviour. Thus, the mechanical properties are improved, if the number and size of surface defects and the surface roughness of the micro bending bars can be reduced. However, an improvement of the surface quality is usually associated with rounding of edges and, in the worst case, the loss of geometrical integrity. Several material and process-related factors were found to influence shape retention and, as a result, surface quality and strength of LPIM ceramic micro parts during the binder removal. To ensure a reproducible fabrication it is necessary to control all material and process-related factors. In this study an interesting opportunity for an in-process improvement of the strength of ceramic micro parts is presented.