Investigation of the degradation and protection of the heat and corrosion resistant high temperature metallic and ceramic surface coating

Materials to be used at high temperatures under corrosive environments need to have enough resistance against such operating conditions. If not, coatings having required resistance can be applied over the surfaces of the base materials. In this study, coatings containing ceramic and metallic components were applied over 304 type stainless steel substrates by using flame spraying as well as glazing. Thermal shock resistance and high temperature corrosion resistance of the coatings were investigated by conducting proper tests on coated substrates. Optical microscopy and scanning electron microscopy (SEM) were used for the investigation of the structural changes that took place in the coatings during testing. Energy dispersive spectroscopy (EDS) in conjuction with SEM was employed for the elemental analyses of the coating layers. X-ray diffraction and high temperature microscopy were utilized to identify the phase structure and the melting behavior of the ceramic coatings, respectively. It was observed that most of the coatings suffered the stresses induced by thermal cycling of the samples. Furthermore, adherence and cohesion of most of the coatings were found to be adversely affected by the chemical composition of the coatings as well as the thermal stresses applied on them. Key words: coating, corrosion, glaze, thermal shock, high temperature microscope