Single-crystal turbine blade tip repair by laser cladding and remelting

High pressure single-crystal turbine blades made from nickel-based superalloys can withstand temperatures of up to 1100 degrees C due to their superior creep and fatigue properties compared to polycrystalline material. However, these parts undergo erosion and cracking due to the extreme conditions they are subject to in the engines of commercial airplanes. Since there is no effective method of repairing these expensive parts, while maintaining the necessary microstructure, the need to develop and establish a reproducible process is of high importance. The process of Laser Material Deposition (LMD) has shown promising results in the building-up of single-crystal or directionally solidified structures, while laser remelting has been shown to extend this monocrystalline height. By combining the two processes, this study aimed to deposit and remelt single-crystal structures on substrates of the nickel-based superalloys CMSX-4 and turbine blade tips of PWA 1426. Experiments were carried out to establish laser parameters that resulted in a monocrystalline microstructure. This study showed that the combination of cladding and remelting can be used to deposit single-crystal structures and was able to establish a reproducible laser process to this effect. The results obtained indicate that the process is a promising candidate for the repair of turbine blade tips and warrants further research into the microstructure and thermomechanical properties of the repaired areas. (C) 2017 CIRP.