Abstract
In this work, an evaluation method of the interfacial strength in thermal spray coating systems by means of an instrumented indentation machine is proposed. Based on the experimental formula for the fracture toughness of monolithic ceramics, we proposed an equation to express the apparent interfacial fracture toughness in function of the maximum indentation load, the apparent Young's modulus at the interface measured by the instrumented indentation machine, the half diagonal length of impression and the half length of interfacial crack. By using the instrumented indentation machine and the proposed equation, the interfacial fracture toughness can be evaluated with small scatter and independent of the loading conditions. The proposed method can be applied to evaluate the interfacial strength of thermal barrier coatings (TBC). The experimental results indicated; (1) The interfacial strength of TBC changed with the thermal fatigue cycle. (2) The interfacial fracture toughness of an actual retired TBC vane was almost comparable to that of the as-sprayed TBC specimen.
