Deformation and fracture of a mudflat-cracked laser-fabricated oxide on Ti

Concentrated heating of titanium by a focused laser beam in ambient atmosphere produces unique dielectric layers with characteristic colors dictated by film thickness and optical properties. A combination of microscopy and diffraction techniques employed to study the phase and microstructure of the oxide coatings showed that nanosecond-pulsed laser irradiation produces polycrystalline TiO films and underlying Ti6O interfacial layers. Mudflat cracking was prevalent in all coatings with most cracks extending through thickness to the metal substrate. Deformation and fracture behavior were probed by traditional nanoindentation methods with accompanying electron microscopy. These mixed titanium oxide coatings have moduli (~200 GPa) and hardnesses (~16 GPa) that are larger than the underlying metallic substrates. Fracture energies and residual stress have also been determined from pre-cracked films; fracture toughness and residual stress tend to decrease with decreasing laser fluence. Electrical contact resistance, measured with conductive nanoindentation, indicates a correlation between laser exposure, current–voltage behavior at constant load, and indentation response. Film conductance increases with decreasing laser fluence, likely due to the presence of defects, which act as a conduction path. Combining techniques provide a unique approach for defining electromechanical behavior and the resulting performance of the films in conditions that cause wear.