Adhesion strength of thermally sprayed coatings is usually measured in accordance with the tensile method specified by ISO 14916. A major limitation of the method, however, is that it cannot measure adhesion strengths greater than that of the glue used to prepare the test specimen. Indentation testing, by virtue of its simplicity and practicality, is a promising alternative in such cases. Collaborative work has been conducted by members of the Japan Thermal Spray Society (JTSS) to establish a standard method for measuring coating adhesion using a conventional Vickers indenter. This paper provides an overview of the experimental and theoretical work that was done and describes the criteria proposed to quantify adhesion strength based on standardized test procedures.

Air plasma sprayed thermal barrier coatings, which reduce the temperature in the underlying substrate material, are an essential requirement for the hot section components of an industrial gas turbine. For TBC systems, the adherence of the top coating is one of the most important parameter for the durability of TBC system. In this work, the thermal fatigue behaviour of an air plasma sprayed thermal barrier coating was investigated. In addition, the residual interfacial strength was also evaluated by means of the 4-point bending test. From the measurement of the AE signals during the thermal fatigue tests, micro-cracking occurred in each cooling stage of the thermal fatigue cycles and then such damage depends on the number of thermal cycle. In addition, TGO grew at the interface with the exposed time at elevated temperature (the time dependent damage). Thermal barrier coating undergoes both time dependent damage and cycle dependent one under thermal fatigue condition. The life of thermal cycle with high temperature dwell time is shorter than not only that of isothermal exposure but also that of thermal cycle without dwell time.