Effects of composite oxide scale on oxidation resistance of superalloy K273

Abstract

A Si-containing K273 superalloy was made using intermediate frequency induction furnace in the study. In the testing of oxidation resistance, the oxidation process of the alloy specimens during the testing at 900 ℃ for 500 h was examined by oxidation weight gain method. The morphology and composition of the oxide scales were determined using scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The effects of the transferring of ions and electrons on the oxidation resistance were further analyzed microscopically by semiconductor oxide models. The results show that the composite oxide scales consist of Cr2O3, SiO2 and spinel-type oxide MCr2O4, with flat and compact structure, and fine grains in uniform distribution. All of these endow the superalloy K273 with strong oxidation resistance. The reason for the powerful oxidation resistance of the composite scale is that the formation process of P+N type semiconductor oxide enables to consume most of the surplus negative and positive ions in the oxide scales, which makes the number of the mobile ions and electrons dropped enormously, and the transfer rate of them falls heavily. So the oxidation rate of the metal phase in the alloy matrix is reduced significantly.

Keywords

• superalloy
• silicon
• oxide scale
• oxidation resistance