MCrAlY alloy bond coat is widely used in thermal barrier coating (TBC) systems to protect substrates from high-temperature oxidizing environments. However, failure of the ceramic topcoat can occur due to a thermally grown oxide (TGO) that grows at the interface between the bond coat and the topcoat. In this study, the effect of chromate treatment was investigated. Prior to topcoat deposition, a thin film of Cr 2 O 3 was formed on the bond coat surface. High-temperature oxidation tests were carried out, and the oxidation rates were determined by inspection of cross sections. Similar oxidation tests were carried out using MCrAlY powder material assumed to be unmelted particles. As a result, the chromate-treated bond coat showed outstanding oxidation resistance. Calculations that take into account the oxidation of particles in the topcoat indicated the generation of internal stress to cause local fracture of the topcoat.

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Thermal spraying is widely used in various industrial fields as effective surface modification method. However, the coating failures such as cracking, debonding and spallation occur due to external loading or internal stress induced by the mismatch of material properties between coating and substrate, and these become a major problem. In this study, mechanical properties of thermal-sprayed ceramic coatings were investigated. Al 2 O 3 and Y 2 O 3 -stabilized ZrO 2 (YSZ) coatings were deposited on plate substrates. Stainless steel plates and aluminum plates, of different thermal expansion coefficients, were used as substrates. The coatings were prepared at two different thicknesses. During deposition of each specimen, the history of substrate temperature was recorded. Four-point bending tests were carried out, while strains at the coating surface and the substrate surface were measured with strain gages. The apparent Young's modulus of the coating was determined using the composite beam theory. Subsequently, the rupture strain of the coating was measured by a three-point bending test. In addition, the residual stresses of the coating were determined by mechanical polishing. The relationships between the results of these tests and the each substrate temperatures during deposition were discussed.

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Thermal spraying is widely used in various industrial fields as effective surface modification method. In this study, mechanical properties of thermal sprayed CoNiCrAlY alloy coating were investigated. The coatings were prepared by three kinds of thermal spray methods. High-temperature exposure of the coated specimens was carried out in the atmosphere. After high-temperature exposure, apparent Young's modulus, strain tolerance, residual stress and hardness of the CoNiCrAlY coating were measured. These tests were also carried out using specimens without high-temperature exposure. As a result, the changes of mechanical properties caused by high-temperature exposure seemed to be correlated with properties of boundary between sprayed particles. From the results, effects of high-temperature exposure on mechanical properties of thermal sprayed CoNiCrAlY alloy coating were discussed.