Laser Metal Deposition (LMD) is an additive manufacturing (AM) and repair technology that has evolved out of conventional laser cladding. As an additive technology, LMD has developed rapidly in the last decade, demonstrating significant potential to reduce costs and lead times for high quality, safety critical aerospace components. This potential can be realised through the reduction of tooling costs and increased material utilisation, both of which have a demonstrable impact on carbon footprint and waste in manufacturing.
Superalloys, such as Inconel 718 (IN718), have an impressive combination of mechanical properties, reliability at high temperatures, and low cost. Superalloys have been increasingly used in several applications, such as in gas turbines as well as in nuclear, oil & gas industries and cryogenic structures due to its excellent strength and aqueous corrosion resistances at low temperatures.
The thin-wall nature of aeroengine components makes LMD an attractive technology; however, there are many factors which affect the final quality and integrity of LMD parts, including the feedstock characteristics, process parameters, geometry, and subsequent heat treatments that are performed. In particular, the temperature transients that LMD parts experience involves rapid solidification, cyclic re-heating, and the potential build-up of heat in previously deposited layers. As a consequence, it is well-known that LMD parts may often exhibit unacceptable levels of distortion and residual stress, as well as unfavourable microstructural features including anisotropy; the precipitation of Laves and delta phases; and the segregation of alloying elements. These features can be removed with specially-designed heat treatments; however, identification of the correct heat treatments requires knowledge of the phase constitution in the part.
SUPERMODEL aims to develop a multi-scale model that links microstructural features to process parameters for laser additive manufacturing of superalloys. This will be achieved through a comprehensive and ambitious combined numerical-experimental programme of work. The overall objectives are to (1) develop and implement a microstructure model and associated process simulation for LMD of 718 and another superalloy; (2) establish and demonstrate a laboratory setup for capturing data to validate the model; (3) carry out a design-of-experiments approach involving the production, monitoring and characterisation of over 100 various samples; (4) validate the model and undertake additional activities on a more complex, multi-material build.
The project has demonstrated the feasibility and successful implementation of a thermo-mechanical-microstructural manufacturing process simulation for LMD of alloy 718 and another superalloy. The validation of the thermal model was within 5%, the distortion and residual stress predictions were within 10% of physical measurements, and the microstructure predictions were within 15% (although more accurate for individual microstructure constituents on the whole).
