Numerical investigation on laser stripping of thermal barrier coating

Thermal barrier coatings (TBC) are extensively used in turbine blades to improve the energetic efficiency of turbines. For repair and reuse of the TBC aerospace components it is necessary to remove the coatings. Present coating stripping process includes, acid stripping and grit blasting of the components which often cause metallurgical damage and dimensional changes. The laser based coating stripping process has recently gained increasing interest due to its high speed, flexibility and ease of automation, although thermal damage pose the biggest threat to its implementation as a replacement to excising machine process. In order to control the thermal damage and improve quality, it is important to understand the fundamental mechanism involved in the laser stripping process. Based on finite element analysis (FEA), a three-dimensional model for simulating the transient temperature field, residual thermal stress and subsequent material removal has been developed to understand the influence of transient thermal characteristic and thermo-mechanical effects on material removal. In addition to the transient temperature field, the model also predicts the dimensions of the ablated profile and substrate thermal damages that occur during the laser stripping process. Experimental results obtained with same process variables using a nanosecond pulsed laser were used to validate the model. Based on the investigation, the mechanism of the material ablation in the laser stripping of TBC is proposed.