HIGH-TEMPERATURE OXIDATION OF (Ti, Cr)C–Ni POWDERS

Abstract

Nickel-clad titanium–chromium carbide powders were subjected to high-temperature oxidation in air at 600–1000 °C. The effect of nickel content (17, 25, and 33 wt.%) on the oxidation resistance of the powders and their oxidation mechanisms was examined. Plasma spraying of the (Ti, Cr)C–Ni powders into water was also conducted to study oxidation processes during spraying. The oxidation rate was found to rise with temperature, with significantly intensified oxidation upon reaching 800 °C. Clad particles of the (Ti, Cr)C–Ni powders with a nickel surface layer in contact with the environment showed higher weight gain during oxidation compared to non-clad (Ti, Cr)C powders. Nickel cladding, depending on temperature, can prevent or slow the oxidation of (Ti, Cr)C particles. With higher nickel content in the powder, the thickness and integrity of the clad layer increased, thereby enhancing oxidation resistance. Analysis of the microstructure and composition of the oxidized powders revealed that multilayer oxide films composed of Ni (NiO) and Ti (TiO₂, Ti_xCr_yO_z) formed on their surface. These films slowed the diffusion of oxygen into the particles but did not stop it completely. At 600–700 °C with 1-h holding, the clad Ni coating partially oxidized with the formation of a surface NiO film but did not fail and retained its integrity. More pronounced degradation and loss of continuity of the clad layer occurred at 800 °C. At 900–1000 °C, the clad Ni layer underwent intense oxidation and was destroyed. The (Ti, Cr)C particles also significantly oxidized, resulting in the formation of a multilayer oxide film based on Ti and Cr (Ti_хCr_yO_z). This film was predominantly porous and did not prevent the diffusion of oxygen into the particles. During plasma spraying of the powder into water, the particles hardly oxidized and retained the microstructure and chemical composition close to the original ones.