I. Buchbender
C. Hoff
J. Hermsdorf
V. Wesling
S. Kaierle

Case Studies of SX and DS Repair by means of Laser Metal Deposition

Advanced Manufacturing and Repair for Gas Turbines (AMRGT2019)
19. März
Type: Konferenzbeitrag
Directionally solidified and single-crystal GT components present a considerable challenge not only during production, but also during repair. The complex investment casting procedures involved in the manufacturing of these parts result in a microstructure that is characterized by small to no grain boundary angles and the directional orientation of all primary dendrites. These characteristics set demanding requirements for the repair of such structures since there is a need to maintain the orientation of the substrate material, while simultaneously ensuring that this is reproduced in the deposited material. The composition of Nickel-based alloys, from which SX and DS components are often made, is characterized by excellent high temperature properties, but low weldability. In addition, the orientation of the dendrites in directionally solidified material make the part highly susceptible to cracking during the thermal treatment by laser when material of the same type is deposited. Despite these difficulties, there arises the need for an effective repair process due to the complex and cost-intensive manufacturing process involved in the production of such parts. This talk presents strategies for the additive repair of SX and DS components by means of laser metal deposition, while employing temperature monitoring and acoustic emissions to characterize the quality of the deposited material. The process of laser metal deposition (LMD) provides the required flexibility and freedom of design, while enabling the targeted application of material to damaged parts. By controlling the local solidification conditions and maintaining the required temperature gradient for directional solidification, the Laser Zentrum Hannover e.V. (LZH) has successfully deposited structures with the necessary microstructure. The use of temperature monitoring and control enables the development of a stable process, while maintaining the required temperature gradient for directional solidification. And the monitoring of acoustic emissions in the form of body-borne noise during the process enables the monitoring of crack and pore formation. The process developed in the scope of this study enables the deposition of Nickel-based alloys of poor weldability to form directionally solidified structures, while monitoring crack formation and temperature essential for a robust process.