Mechanical and electromechanical behavior of oxide coatings grown on stainless steel 304L by nanosecond pulsed laser irradiation

Nanosecond-pulsed laser exposure of an austenitic stainless steel 304L in ambient atmosphere produces dielectric oxide coatings with characteristic colors. From an industrial perspective, these oxide layers are particularly interesting for use as unique authenticity identifiers on welded or sealed components. Processing parameters control oxide thickness and residual stresses. The combined properties of the oxide–substrate system control deformation, fracture, and electromechanical behavior. Instrumented nanoindentation indicates that oxide mechanical properties are dictated by film thickness. While elastic modulus is relatively insensitive to laser processing conditions and has an average value of ~ 150 GPa, hardness decreases sharply as film thickness decreases below 100 nm. Indentation coupled with electron microscopy as well as conducting nanoindentation suggest that both fracture behavior and electromechanical response are a function of laser processing; thick oxides fracture circumferentially upon indentation while thin oxides undergo radial cracking and thinner laser oxides are typically more conductive than their thicker counterparts.