Millisecond pulse laser machining of thermal barrier coatings

Abstract

Ceramic thermal barrier coatings (TBCs) are extensively used in aero-engine and gas turbine components such as blades, vanes, and combustor linings to improve energetic efficiency. Controlled removal of TBCs is essential for various reasons, including repair or reuse of the TBC coated components and as a preliminary process for drilling of cooling holes over the coated components, among others. The nanosecond laser-based coating removal process has been widely researched due to its high-quality results, ease of automation, and flexibility, however, the process is relatively slow and not ideal for industrial exploitation. This research investigates the use of millisecond pulsed laser machining processes for removing the TBCs from an aerospace alloy substrate and demonstrates it as a viable alternative to the current state-of-the-art nanosecond laser ablation. The thresholds for machining of the TBCs and the nickel alloy substrate have been established, and the fundamental mechanism behind the millisecond laser removal of TBCs has been discussed in detail, based on the results from experiments and numerical modelling. The millisecond laser machining process is significantly faster than the nanosecond laser ablation and at the same time produces quality that is acceptable for industrial applications.