Laser cladding of high performance ceramic sheets on a low quality ceramic substrate

Abstract

High alumina refractory ceramics offer increased resistance in slagging environments. In particular, the presence of more than 5% Cr2O3 in a high alumina refractory ceramic increases its slag corrosion resistance due to the formation of a dense Cr-spinel oxide layer at the refractory/slag interface. However, refractory ceramics containing more that 5% Cr2O3 cost significantly more than Cr2O3-free refractory ceramics. The surface and near-surface compositions and properties are more important than the bulk properties for high-temperature applications in slag-containing environments. Laser cladding, therefore, is a useful tool for developing refractory ceramics with a low-cost substrate and a high slag-corrosion resistant surface layer. This paper presents a technique involving cladding of pre-positioned layers of a 85% Al2O3–5% Cr2O3 ceramic on a 60% Al2O3 refractory ceramic, focusing on the process characteristics. A simple model that describes the process of multi-sheet cladding is developed and the operating map for the process is presented. The microstructural characteristics of the clad surfaces have been analysed by optical and scanning electron microscopy (SEM), as well as energy dispersion X-ray spectroscopy (EDX), revealing the formation of an intermediate layer between the substrate and the top ceramic sheets in multi-sheet cladding. A bi-phasic structure is formed in the clad surface, comprising of an Al2O3–Cr2O3-based solid solution and a SiO2-based matrix.