TY - JOUR

T1 - Thermally sprayed nickel-based repair coatings for high-pressure turbine blades

T2 - Controlling void formation during a combined brazing and aluminizing process

AU - Nicolaus, Martin

AU - Möhwald, Kai

AU - Maier, Hans Jürgen

N1 - Funding Information: Funding: Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project number 119193472.

PY - 2021/6/16

Y1 - 2021/6/16

N2 - Turbine blades must withstand severe loading conditions and damage can occur during operation due to heat, pressure, foreign objects and hot gas corrosion, despite the protective coatings applied onto the turbine blades. Instead of replacing the damaged components, maintenance, repair and overhaul are key to extend the total service life. Besides welding, the repair of turbine blades by brazing is an established repair process in the industry and involves many individual steps that often require a high degree of manual work. In the present study, a hybrid joining and coating technology was developed to shorten the state-of-the-art process chain for repairing turbine blades. With this approach, a repair coating, which consists of a filler metal, a hot gas corrosion protective layer and an aluminum top layer, is applied by atmospheric plasma spraying. The coated turbine blade then undergoes a heat-treatment so that a brazing and aluminizing process is carried out simultaneously. Due to diffusion and segregation processes, pores can occur in the heat-treated coating. In the present study, a full factorial design of experiment was performed to reduce the pores in the coating. The microstructure of the repair coating was investigated by optical-and scanning electron microscopy (SEM), and the impact of the process parameters on the resulting microstructure is discussed.

AB - Turbine blades must withstand severe loading conditions and damage can occur during operation due to heat, pressure, foreign objects and hot gas corrosion, despite the protective coatings applied onto the turbine blades. Instead of replacing the damaged components, maintenance, repair and overhaul are key to extend the total service life. Besides welding, the repair of turbine blades by brazing is an established repair process in the industry and involves many individual steps that often require a high degree of manual work. In the present study, a hybrid joining and coating technology was developed to shorten the state-of-the-art process chain for repairing turbine blades. With this approach, a repair coating, which consists of a filler metal, a hot gas corrosion protective layer and an aluminum top layer, is applied by atmospheric plasma spraying. The coated turbine blade then undergoes a heat-treatment so that a brazing and aluminizing process is carried out simultaneously. Due to diffusion and segregation processes, pores can occur in the heat-treated coating. In the present study, a full factorial design of experiment was performed to reduce the pores in the coating. The microstructure of the repair coating was investigated by optical-and scanning electron microscopy (SEM), and the impact of the process parameters on the resulting microstructure is discussed.

KW - Aircraft overhaul

KW - Aluminizing

KW - High-temperature brazing

KW - Hybrid technology

KW - Protective coatings

UR - http://www.scopus.com/inward/record.url?scp=85108870921&partnerID=8YFLogxK

U2 - 10.3390/coatings11060725

DO - 10.3390/coatings11060725

M3 - Article

AN - SCOPUS:85108870921

VL - 11

JO - COATINGS

JF - COATINGS

SN - 2079-6412

IS - 6

M1 - 725

ER -