The aim of this work is to study the application of microwave sintering to consolidate yttria-stabilized zirconia polycrystalline (Y-TZP) ceramics commonly applied in dentistry, so as to obtain highly dense materials and fine microstructure with shorter sintering cycles. Three Y-TZP materials are considered: two commercially available for dental applications and one laboratory studied powder. Microwave sintering was carried out at 1200 and 1300 ºC for 10 min and conventional sintering at 1300 and 1400 ºC for 2 h. Relative density, Vickers hardness and fracture toughness values for sintered samples were determined. Microwave sintering results, generally, in improved mechanical properties of the materials in terms of hardness and fracture toughness compared to conventional sintering and, in some cases, at lower sintering temperatures.A finer grain microstructure (final grain size < 250 nm) was obtained with microwave sintering for both commercial materials. Fracture toughness values differ significantly between sintering techniques and chosen parameters. These results suggest that 2 microwave heating can be employed to sinter Y-TZP commercial ceramics for dental applications obtaining improving the mechanical properties of the materials with a very important time and energy consumption reduction.
Different factors such as the characteristics of starting powders, their processing, the sintering technique and the final sintering temperature were assessed with the goal to improve the low temperature degradation (LTD) resistance of 3Y-TZP materials without compromising on the mechanical properties. The degradation of hydrothermally treated specimens was studied by AFM, nanoindentation technique, micro-Raman spectroscopy and electron microscopy.3Y-TZP previously prepared in laboratory by colloidal processing, and sintered by microwave method at low temperature (1200 ºC) led to excellent mechanical and LTD resistance, as compared to dental restorations based on Y-TZP commercial material. In the former, the presence of m-phase was almost non-existent even after 200 h of exposure to LTD conditions and the initial mechanical properties were maintained, giving 16 GPa and 250 GPa mean values for hardness and Young's modulus, respectively. The influence of the fast-technology by microwave heating is presented with a non-conventional sintering method to fabricate 3Y-TZP 2 ceramics for dental application with very high resistance against LTD and optimized mechanical properties.
Innovative techniques for materials processing that result in shorter times and lower energy consumption than conventional methods, such as microwave sintering, are currently under investigation in order to obtain fully-consolidated ceramic materials. Microwave sintering has important effects on the resulting properties of zirconia-based ceramics, which, in turn, affect its performance and durability, as in the case of their susceptibility to low temperature hydrothermal degradation (LTD), an ageing phenomenon that deteriorates their mechanical performance. The purpose of this work consists on assessing the effects of microwave sintering on the microstructure and mechanical performance of zirconia composites by comparing it to conventional sintering. Resistance to LTD of 3Y-TZP-only materials has also been evaluated. The results obtained in this work suggest that microwave sintering can reduce processing times and sintering temperatures when compared to conventional sintering while still obtaining dense zirconia-based ceramics and complying with the expected mechanical properties. At the same time, an increase in the resistance to LTD is also observed.
The fretting wear behavior of self‐mated Y‐TZP dental materials obtained by nonconventional microwave and conventional sintering has been investigated. Two 3Y‐TZP materials, a widely utilized commercial dental ceramic (LAVA) and a lab‐prepared 3Y‐TZP powder based equivalent have been assessed. Relative density and mechanical properties as well as the grain size variations upon sintering have been evaluated. After exposure to selected gross slip regime fretting wear conditions, the wear tracks have been characterized allowing the measurement of the coefficient of friction, track profiles, and pit features. The results indicate that microwave sintering results in a similar fretting wear behavior as observed for conventional‐sintered 3Y‐TZP, as the measured volumetric wear loss is of a comparable order of magnitude. Regarding the influence of the grain size, the analysis revealed that a large grain size (>300 nm) results in an increased wear volume and that a higher resistance to fretting wear is constrained to a mid‐range particle size (100–250 nm). Since the fracture toughness of all investigated ceramic grades was comparable, the influence of the fracture toughness on fretting could not be assessed. Abrasive grooving, delamination, and microcracking have been identified as major wear mechanisms inside the wear tracks for both conventional‐ and microwave‐sintered 3Y‐TZP. In general, microwave sintering can provide 3Y‐TZP dental materials with a comparable fretting wear resistance as that observed for conventional sintering using lower dwell sintering temperatures and a shorter processing time.
Dental pieces are subjected to constant friction due to grinding during mastication and mouth disorders such as bruxism. Therefore, wear resistance of Y-TZP materials used for dental prostheses must be investigated. In this work, the influence of humidity and low temperature hydrothermal degradation (LTD) in 3Y-TZP ceramics subjected to fretting has been evaluated. A 100% r.h. reduces the effects of wear due to the lubricative effect of water, compared to those at ambient r.h. COF, wear volume and damage are considerably lowered at a r.h. of 100%.Exposure to degradation conditions for 25 h increased the vulnerability to wear damage of LAVA grade Y-TZP sintered at 1400 °C since the critical grain size of 300 nm was exceeded.
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