Surface oxidation phenomenon and mechanism of AISI 304 stainless steel induced by Nd:YAG pulsed laser

Abstract

• Oxidation phenomenon in one laser spot on stainless steel surface is studied. • Compositions and morphologies vary from center to edge in one laser spot. • Hexagonal Cr 2 O 3 distributes in the edge, while spherical Fe 2 O 3 in the center. • Oxidation mechanism is proposed based on thermodynamics and kinetics. Surface oxidation phenomenon of AISI 304 stainless steel induced by Nd:YAG pulsed laser in air was investigated using scanning electron spectroscopy (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that there were different morphologies and phase compositions in one laser spot from the center to the edge on stainless steel surface after pulsed laser oxidation. The morphologies were mainly nano-spheres and hexagons. It was proved using XRD that they were basically γ-Fe, Cr 2 O 3 , Fe 2 O 3 and a small amount of MnO 2 . The elemental compositions in the edge region were rich in Cr and deficient in Fe, while it had an opposite distribution trend in the center of the laser spot. XPS measurement confirmed the formed oxides on the stainless steel surface, indicating that most of the elements were in oxidation states. Moreover, the oxidation behavior of the stainless steel in one laser spot was assessed using thermodynamics and kinetics of laser oxidation process. And the oxidation mechanism was also clearly revealed.