Analysis of oxidation behavior of Ni-base superalloys by laser-induced breakdown spectroscopy

Abstract

The application of laser-induced breakdown spectroscopy (LIBS) to elemental depth profile analysis of high temperature oxidation behavior of Ni-based superalloys is presented. An oxidation test of two Ni-base superalloys, Alloy 617 and Haynes 230, to be considered as the most promising candidates for very high temperature reactor (VHTR), was carried out in dry air at 900 °C. A duplex external oxide layer of MnCr₂O₄ and Cr₂O₃ with internal Al₂O₃ oxides was mainly formed in both alloys. In addition, in Alloy 617, Ni and Ti enriched oxides were observed at the surface unlike in Haynes 230, and Alloy 617 was more susceptible to intergranular oxidation. Generally, the oxidation of Alloy 617 was more extensive than that of Haynes 230, i.e. Alloy 617 formed a thicker oxide layer of ∼8 μm, compared with Haynes 230 with an oxide layer of ∼5 μm in thickness after 1000 h. Depth profiles obtained by LIBS are found to be in broad agreement with those obtained by established techniques such as X-ray diffraction (XRD), scanning electron microscopy coupled to energy dispersive X-ray spectrometry (SEM-EDS), and secondary ion mass spectrometry (SIMS).