DEVELOPMENT OF ADDITIVE MANUFACTURING GAS TURBINE HOT GAS PATH VANES AT BAKER HUGHES

This paper describes the efforts, the lessons learned and the success that led, over a period of 5 years, to the development, validation and finally industrialization of high-pressure turbine vanes manufactured with additive Direct Metal Laser Melting (DMLM) technology. The introduction of the study collects the requirements for gas turbine vanes in the range of F class and identify the material's grade and chemical composition of the alloys. As well it is summarized the conflict among the processability and desirable mechanical properties of Nickel base alloys. The paper explains the procedure used to simultaneously optimize the alloy and the DMLM process parameters for a Nickel based superalloy with high gamma prime content to manufacture complex geometries as high-pressure vanes in the turbine hot section. Metallurgical defects formation in additively manufacturing superalloys are strongly linked to process parameters, such as laser power, scan speed, layer thickness, scan strategy, etc. but are also directly linked to the specific geometry of the component to be processed. Contouring parameters as downskin/upskin that have higher influence in the residual stresses of the parts and lead to a mechanical properties debit to fatigue resistance. A "fast-work" approach was used starting with a limited validation of the components in a back-to-back comparison with the traditional technology in lab environment. Over the standard mechanical testing samples, it is introduced subsize component mechanical testing and full-scale component thermal cycle above 1'000 degrees C. A second step to mature the technology has been to produce and install a first set of vanes and shrouds to be tested in a real validation engine to verify resistance to the main failure modes, in particular cyclic type of damage as low cycle fatigue and crack propagation. In the paper the final validation step is also presented. In this phase the components are installed in a production engine and monitored by periodic inspections. This allows to complete the durability assessment in real service environment. The work is completed with an overview on the industrialization challenges of the technology. It has been provided guidelines in components design and printing strategy to mitigate macro cracks formation on high gamma prime content material, including post-print processes as EDM cut removal, thermal and surface treatments. It is finally compared the CO2 footprint of additive technology versus investment casting, demonstrating a significative reduction in the CO2 emission in gas turbine vanes manufacturing process using additive technology.