Removal of Thermal Barrier Coating by Laser Cleaning

BACKGROUND: Various types of coatings are used for corrosion and wear protection of structural materials and thermal insulation. Coatings that are used in high-temperature conditions, e.g. aircraft and industrial gas turbine engines, have the most complex structure. They are used to isolate the turbine components from the hot gas flow, increasing the durability and energy efficiency of engines [1]. Thermal barrier coatings have three main requirements, including low thermal conductivity, stability at high temperatures, and high durability, and they are fairly difficult to remove. AIM: To solve the problem of removing thermal barrier coating from moving blades of gas turbine engines subjected to intensive wear in tough operating conditions. Laser cleaning technology is proposed as the most effective cleaning method. It is an advanced technology that allows finding solutions to reduce production costs and increase the performance and quality of processes [2]. The paper discusses the importance of preserving the basic blade material during thermal barrier coating removal for its subsequent use (new coating). The aim is to remove the thermal barrier coating without damaging the basic metal and to determine the optimal conditions for such works. METHODS: To achieve the aim, the blade made of CS70-VI alloy was cut into several parts along the length of the airfoil; one part was selected as a check test piece that was not cleaned. The remaining test pieces were tested during laboratory experiments aimed at studying the influence of input laser cleaning parameters on the removal of the thermal barrier coating. All samples were then subjected to metallographic tests to determine the material structure, microhardness, and thickness of the thermal barrier coating. RESULTS: The paper presents metallographic analysis of microhardness and thickness of thermal barrier coating after testing confirming the effectiveness of laser cleaning to ensure the durability and reliability of moving blades for gas turbine engines. CONCLUSION: The study involved a literature review of papers related to laser cleaning. Next, we selected the variation ranges of the main processing parameters and conducted a series of experiments followed by the metallographic analysis of test pieces. Metallographic analysis allowed to determine the conditions ensuring complete removal of the thermal barrier coating and the relationship between the thickness of the thermal barrier coating and the radiation power.