Plastic metallic-barrier layer for crack propagation within plasma-sprayed Cu/ceramic coatings

Abstract

The interfacial reactions of the plastic Cu-metal barrier layer in the Al2O3–40 wt% TiO2 (AT40) composite coating prepared by plasma spraying and its effect on the crack propagation behaviour during thermal cycling were investigated. The phenomena of Cu dendrites appearing on the upper surface of the Cu layer and the Cu whiskers growing along the crack of the ceramic coating under the Cu layer after thermal cycling (900 °C, Ar), and the formation mechanism are explained using FE-SEM, XRD, EPMA, and EBSD. The Cu dendritic and Cu whiskers changed the stress state of the interface and enhanced the anti-crack-propagation ability of the coating. In addition, nanoparticles surrounding the Cu layer using EBSD were observed in the Cu particles added to the AT40 coatings (C-AT coating) by plasma spraying. The calculations of surface energy indicated that the nanoparticles improved the wettability of the interface and promoted the interfacial coupling behaviour. A model of the relationship between stress and crack propagation in the process of heating and cooling was used to analyse the effect of the plastic metallic-barrier layer (Cu) on crack propagation. This work demonstrates that the Cu layer improved the anti-crack-propagation ability of the coating. Such C-AT coatings may find potential applications in high-temperature materials and wear-resistant material surfaces.