Mechanism for Control of Laser-Induced Stainless Steel Oxidation

This paper presents the development of a model for Nd:YAG laser surface oxidation of 316L stainless steel. A full factorial design of experiments (DOE) are implemented to produce a model for the prediction of elemental composition and color. The elemental composition of the films produced where measured using an X-ray photoelectron spectroscopic (XPS) and the color is measured using optical reflectance spectroscopy. Oxide layers produced have a Cr/Fe ratio in the range of 0.13-2.09, and highly controllable color variation via single-pass laser process. The effect of the process parameters used such as power, frequency, and scan speed on laser-induced oxides is examined with an aim to produce a model suitable for predictive control of the elemental composition and color of the oxide film. Surface morphology control via alteration of the laser power is an important factor for defining the resulting coloration. A new finding from this work is the discovery that within the range of laser surface processing parameters investigated, the molybdenum concentration is inversely proportional to the chromium concentration. This paper provides data required for control of 316L-SS surface chemistry, and for the expansion of the current thermokinetic model to incorporate the mechanistic effect of molybdenum. This paper outlines a model for Nd:YAG laser surface oxidation of 316L stainless steel. Through full factorial design of experiments, it predicts elemental composition and color variations. X-ray photoelectron spectroscopy and optical reflectance spectroscopy measure film composition and color. Process parameters such as power and frequency influence oxide characteristics, revealing an intriguing inverse relationship between molybdenum and chromium concentrations. image