Abstract

Additive manufacturing technologies have been successfully developed and qualified for Industrial gas turbine hot gas path components, such as nozzle, blades and combustion component (fuel nozzle). Direct metal laser sintering (DMLS) and direct metal laser deposition (DMLD) have been used as a unique enabler for repair of Cobalt based and Ni based superalloy components, as a hybrid on to conventionally manufactured parts that have seen service exposure. Four different repair applications will be showcased. The first includes repair of an investment case Stage 1 nozzle made of FSX414 repaired using DMLS CoCrMo, via a TIG welding process using a Nozzalloy^TM filler wire. The development of the additively manufactured coupon, including detailed microstructural and mechanical property characterization, suited for a > 900°C application, will be presented. An optimized DMLS process that eliminates HIP (hot isostatic pressing) was developed for the CoCrMo alloy, and the effect of subsequent heat treatment that led to a microstructure which enabled superior creep properties in the DMLS CoCrMo, will be presented. The second case will be the development of a crack free directionally solidified (DS) nickel-based superalloy MarM247LC via DMLD technology. MarM247LC is an extremely difficult to weld superalloy and undergoes liquation cracking or strain age cracking, during repair and refurbishment. Attempts to restore the MarM247LC structure via conventional processes such as welding and brazing have resulted in, at best, an equiaxed microstructure with cracks.  In this study, the DMLD process was used to build MarM247 on a seed of cast DS MarM247LC via a systematic design of experiments, by varying the laser power, scan speed, powder feed and step over. An epitaxial growth of the DMD structure on the cast DS seed was established and columnar grains were seen to grow (with a misorientation of < 9^o on the cast seed). Detailed characterization revealed a very fine dendritic structure in the DMD build. A detailed characterisation of the primary dendrite spacing, inter-dendritic segregation as well as precipitate size and volume fraction and tensile properties, was carried out in the as-built condition and after heat treatment. The third case study will showcase the successful repair of a fuel nozzle swirler ring for a duel fuel configuration gas turbine, of IN718, Maraging steel and L605 (cobalt based alloy) on to a stainless steel using the DMLD process. All three case studies demonstrate the ability to use additive manufacturing as a unique technology enabler for repair of high temperature superalloys. The work was carried out as part of collaborative project with Indian Institute of Science, Bangalore, INTECH DMLS, Pvt. Ltd. (DMLS process), and DM3D, Michigan USA (DMLS process), and GE, Power, Repair Development Center. GE, India Industrial Pvt. Ltd., Bangalore, and while DS was with GE Power, KB and PS were at the Indian Institute of Science.