Modification of single-crystalline yttria-stabilised zirconia induced by radiation heating from laser-produced plasma

Thermal modifications induced by intense laser pulse irradiation of a material surface are studied. Single-crystalline yttria-stabilised zirconia (YSZ) is irradiated with Joule-class intense laser pulses with three focal intensities of 10(12), 10(13), and 10(17) W cm(-2) at pulse durations of 15 ns, 300 ps and 110 fs, respectively. The physical surface properties of the irradiated YSZ are determined using an optical digital microscope, a scanning electron microscope and x-ray diffraction methods. In all three cases, a linear scratch pattern along the crystal orientation on the YSZ surface is found, which surrounds the laser irradiation spot area (diameter: 60 mu m). In the 15 ns case, the focal spot area is polycrystallised with a tensile residual stress of 0.45 +/- 0.05 GPa. However, the linear scratch pattern of 1.8mm in diameter remains in the single-crystalline phase of YSZ, having a residual stress below the detection limit. A two-dimensional radiation-hydrodynamic simulation reveals that a radiative plasma source generated on the focal spot by the laser irradiation ablates the material surface. A region of approximately 1.4mm in diameter is affected by an ion temperature beyond 0.25 eV; hence, ablation of the material surface to a thickness of 1 mu m order is observed. The diameter of this simulated ablation region is consistent with that of the linear scratch patterns observed in the experiments to within a factor 1.3. The findings of this study indicate that a large area relative to the laser focal area can be modified by radiation heating in a laser-induced material modification process. These lead to a reasonable modification depth of 10 mu m, potential hardness improvement for metal materials and visible benchmark in analysis by simulation to understand the laser-material interaction.