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The influence of electrical discharge machining (EDM) on thermal barrier coating (TBC) in a two-step drilling of nickel-based superalloy has been studied. The TBC was coated on the superalloy using electron beam physical vapor deposition (EB-PVD). Simulation result shows that the temperature at TBC/metal interface increases with pulse-on time and peak current. The temperature will exceed the melting point of the coating material when using relatively large pulse energy. Experimental result reveals that large pulse-on time or high peak current caused defect such as cracking at coating sidewall and delamination at the TBC/metal interface. For EDM drilling holes with inclined angle, the leading edge had worse condition of debris evacuation, and consequently caused secondary discharge which resulted in melt and spalling of the coating material. In addition, relatively larger pulse-on time and greater peak current might result in greater thermal stress gradient at the interface and subsequently lead to cracking or spalling at the coating layer. Therefore, process conditions of short pulse-on time, longer pulse-off time, and small peak current are recommended for EDM drilling of the EB-PVD coated nickel-based superalloy. [ABSTRACT FROM AUTHOR]

The possibility of using vibroacoustic signals for monitoring the efficiency of discharge pulses during electrical discharge machining is examined. Data on the effect of the variable dynamic characteristics of billets and background noise for electrical discharge machining in different frequency ranges on the parameters of vibroacoustic signals are presented. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) are used to provide thermal insulation for superalloy components from high-temperature gas streams. Due to the insulativity of the top coat and the different physical and chemical properties of each layer, it is difficult to machine small holes in TBC-coated components. In this paper, electrical discharge machining (EDM) was used to machine small holes in high-velocity oxy-fuel-sprayed TBC-coated nickel superalloys using the assisting electrode method. The signal-to-noise (S/N) ratio of the experimental results was used to study the influence of the processing parameters on the response characteristics. Based on the S/N ratio results, the machining parameters of multiple responses were optimized using the gray relational analysis method. Experiments were conducted using an orthogonal array, and the factors selected in this study were peak current, pulse duration, duty factor, and flushing pressure. The responses (i.e., machining time (MT), electrode wear (EW), maximum falling distance of 8 %YO-stabilized ZrO (MFD-YSZ), and surface roughness (Ra)) were chosen to evaluate the effects of machining. The results showed that peak current influences MT, EW, Ra, and MFD-YSZ more than the other factors and that pulse duration is the most significant factor for multiple responses. A confirmation experiment showed that the optimal process parameters improved the gray relational grade index for the multiple responses from 0.7393 to 0.7785. [ABSTRACT FROM AUTHOR]