Textured alumina/zirconia composites fabricated via Digital Light Processing (DLP)
COPPOLA B. 1, SCHMITT J. 2, MONTANARO L. 1, PALMERO P. 1
1 INSTM R.U. Lince Laboratory, Department of Applied Science and Technology (DISAT), Politecnico di Torino, Torino, Italy; 2 Laboratoire de Synthèse et Fonctionnalisation des céramiques (LSFC) UMR 3080 CNRS/SAINT-GOBAIN CREE, SAINT-GOBAIN RESEARCH PROVENCE, Cavaillon, France
Ceramics microstructural texturing is a very advantageous approach to enhance mechanical and/or functional properties along preferred directions. For instance, the presence of aligned platelets within a ceramic matrix has been shown to improve the fracture toughness, favouring mechanisms of crack deflection, crack bridging, and grain pull-out. Textured ceramics have been fabricated through various methods: tape casting, magnetic field, ice templating and gravitational settling. However, traditional ceramics shaping presents limitations in terms of geometries and always require a post-production machining to have more complex geometries. Nowadays, these issues can be overcome by 3D-printing technologies, successfully used to produce technical ceramics, such as alumina and zirconia, expanding the design freedom and improving the process speed. Up to know, to the best of our knowledge, no research has ever dedicated to the 3D-printing of textured alumina/zirconia ceramics. Therefore, in this research, alumina/zirconia composites, in which alumina platelets are embedded in a fine zirconia matrix, have been fabricated via digital light processing (DLP). Aim of the study is to prove the feasibility to exploit DLP in the fabrication of advanced textured ceramics, and to correlate composition (in terms of alumina platelets/zirconia ratio) and microstructure with physical/mechanical properties. In fact, in the available DLP equipment, the movement of the slurry under a doctor blade generates a shear field, which could be able to align the anisotropic particles dispersed in the slurry. First, different formulations were optimised in terms of rheological properties, mixing suitable amounts of micrometer-sized alumina platelets, 3 mol% yttria-stabilized zirconia, dispersant and photocurable resin. Indeed, slurry optimisation is a crucial step both for a successful 3D-printing and adequate alumina platelets orientation. In a first attempt, aimed at proving the capability of DLP to induce platelets orientation, a formulation based on alumina platelets dispersed in the resin (i.e., without zirconia particles, referred to as AZ0), was used. Then, two alumina platelets/zirconia formulations (AZ15 and AZ85, respectively, where the numbers 15 and 85 denote the platelets amount in the composites), were prepared at 42 vol% solid loading, with an optimized dispersant amount. After printing parameters optimization, the three formulations were successfully 3D-printed via DLP. Then, samples were firstly thermal debound and then sintered for 1 h at 1625°C in the case of AZ0 and 1550 °C for alumina platelets/zirconia composites. Microstructural observations allowed to observe a very high orientation degree of the alumina platelets, fully demonstrating the ability of the technique to produce texturing. However, the composite AZ85 showed a poorly densified microstructure, with significant porosity between the alumina platelets, probably due to a too low zirconia amount. On the opposite, the AZ15 composite showed a higher density, even if some pores were observed. In spite the microstructure could be further optimized, the material showed a high flexural strength of approx. 840 MPa, which encourages further research. Indeed, considering the great efficacy of the employed 3D-printing process for the preparation of highly textured alumina/zirconia ceramics, Single-Edge Notched Bending (SENB) tests are planned, to investigate the influence of well-oriented alumina platelets on alumina/zirconia composites fracture toughness.