Relations between Mechanical Properties of Thermal-Sprayed Ceramic Coatings and Substrate Temperature during Deposition

Abstract

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. Al₂O₃ and Y₂O₃-stabilized ZrO₂ (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.