Author:

Keywords:

G095920N#55522169, C3/20/084#55984787, I001120N#55949025

Abstract:

Zirconia-based ceramics exhibit great potential for implant applications due to their outstanding material properties. Laser surface texturing is a promising method for modifying the surface properties of implant materials, thus achieving specific desired functionalities. This research aims to achieve precise and efficient surface texturing of zirconia-based ceramics, while mitigating negative effects on material properties, enabling tailored functionality for specific implant applications using ultrashort pulsed lasers. Three aspects are covered in this research: 1) the fundamental study about laser interaction with the zirconia-alumina nanocomposites, including theoretical modeling; 2) the detailed investigation of the influence of process parameters and material composition on machining performance; and 3) the effects of laser surface texturing on the mechanical properties and hydrothermal aging of alumina toughened zirconia (ATZ). Starting from an unusual inhomogeneous phase melting phenomenon observed in a single pulse laser ablation experiment, where the zirconia phase with a higher melting point was melted while the alumina phase remained solid, the fundamental mechanisms that occurred during ultrashort pulsed laser interaction with the nanocomposites were investigated. Theoretical modeling indicated that the zirconia phase absorbed significantly more laser energy than the alumina phase due to its smaller band gap owing to the nonlinear strong field ionization mechanism. The ultrashort duration of the laser pulses ensured that the energy absorption was completed in a timescale where thermal diffusion played a minor role. This means that the absorbed laser energy was concentrated within individual grains, resulting in a much higher temperature in the zirconia grains compared to the alumina grains. Based on this result, a method for selectively removing the lower band gap phase of a composite using ultrafast laser was proposed. By carefully controlling the applied laser fluence, selective removal of the zirconia phase without damaging the surrounding alumina phase was demonstrated. It is worth noting that this method can be applied to other composite materials that have band gap contrast among their constituent phases. In addition to the selective phase removal method, which is an example of applying the inhomogeneous laser heating behavior, this distinctive inhomogeneous laser heating behavior also resulted in a unique material removal mechanism during the ultrashort pulsed laser micromachining process. Specifically, the top layer of the nanocomposite disintegrated due to the localized melting of the higher melting point zirconia grains. This peculiar phase melting phenomenon indicated that material ablation occurred under strong nonequilibrium thermal conditions during ultrashort pulsed laser micromachining. The unique material removal mechanism suggests that altering the relative proportion of constituent phases can impact the material removal behavior in ultrashort pulsed laser processing. Therefore, in addition to the laser parameters, the influence of material composition on laser processing performance was also investigated. Based on the results, a general guideline was provided for the easy selection of laser parameters to meet specific practical application requirements. In the last part of the research, the impact of laser surface texturing on the mechanical properties and hydrothermal aging of ATZ was evaluated. An alternative approach, involving laser texturing of pre-sintered materials followed by sintering, has been proposed to mitigate the adverse effects of laser surface texturing, thereby enhancing the reliability of the surface-textured materials for potential applications.