Ultrashort pulsed laser ablation of zirconia toughened alumina: Material removal mechanism and surface characteristics

Zirconia toughened alumina (ZTA) is commonly used in hip joint implants and cutting tools. The difference in material properties of the zirconia and alumina phases makes the composite inhomogeneous at the grain size level. Due to the strong nonlinear laser absorption mechanisms of wide band gap materials under intense laser field, the smaller band gap zirconia phase can absorb a significantly larger amount of laser energy than the alumina phase. The nonuniform energy deposition and lattice heating takes place at a comparable timescale as the laser pulse duration, which is too short for thermal diffusion to play a role. As a result, the temperature in the zirconia phase can be significantly higher than in the alumina phase, leading to a unique selective phase melting phenomenon, i.e. localized melting of the higher melting point zirconia phase (2715 degrees C) surrounded by a lower melting point alumina phase (2072 degrees C) which remains solid. This phenomenon makes the material removal mechanism of the nanocomposite significantly different from that of single-phase materials under ultrashort pulsed laser processing. On the basis of experimental analysis and theoretical modelling, material ablation by the disintegration of alumina grains due to the localized melting of the zirconia phase was identified.