Superalloys 2024: General Session 7: Repair and Refurbishment
Program Organizers: Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346
Wednesday 8:30 AM
September 11, 2024
Room: Exhibit Hall
Location: Seven Springs Mountain Resort
Session Chair: Fernando Pedraza, Universite De La Rochelle; Iuliana Cernatescu, Pratt and Whitney
8:30 AM
Improving Repair Braze Gap Strength Through the Development of a Novel Superalloy Filler: Dirk Reker1; Roman Sowa2; Caspar Schwalbe3; Bernd Boettger4; Frank Seidel1; Marco Panella3; Kai Moehwald5; Martin Nicolaus5; Wolfgang Tillmann6; 1MTU Maintenance Hannover; 2MTU Aero Engines Polska; 3MTU Aero Engines; 4ACCESS e.V.; 5Institute of Materials Science, Leibniz Universität Hannover; 6Institute of Materials Engineering, TU Dortmund University
Superior repair technology is a principal driver for resource-effective operation in the aviation industry. Routine operation of aircraft engines exposes the turbine components to high stresses and high temperatures. To withstand extreme operational conditions Ni-based superalloys are used to manufacture turbine components. A crucial factor in targeting the assurance of repair reliability is improving the repair braze gap strength. This study seeks to improve the braze repair strength by optimising a novel superalloy filler material. The superalloy filler material acts as a complementary additive, that is blended with the braze alloy in powder form and improves the joint properties after brazing. The novel superalloy filler was developed by materials simulation using the CALPHAD (CALculation of PHAse Diagram) approach. Phase field modelling using MICRESS® was applied to study the brazing kinetics and microstructure evolution. The developed superalloy filler was experimentally validated in respect to microstructure improvement and mechanical potential by tensile testing at elevated temperature (871 °C). The application of the novel superalloy filler shows an increase in ultimate tensile strength in comparison to a conventional braze blend.
8:55 AM
Mechanical Properties of Waspaloy Repaired by Laser Metal Deposition and Cold Metal Transfer: Alice Cervellon1; Marjolaine Sazerat2; Romain Bordas2; Lucie Barot1; Sophie Gillet1; Azdine Nait-Ali2; Patrick Villechaise2; Roland Fortunier3; Jonathan Cormier2; 1Safran Aircraft Engines; 2Institut Pprime - ENSMA; 3LTDS - ENISE
The microstructure and mechanical properties of additively manufactured Waspaloy were characterized in the industrial context of refurbishment. Two processes were studied to discuss their advantages and drawbacks considering the targeted application: Laser Metal Deposition with powder and Cold Metal Transfer. The resultant microstructures were compared in the build-up and at the interface between the wrought base Waspaloy and the additively manufactured part, in the as-built condition and after post weld heat treatments. Tensile and creep properties were studied along three directions - horizontal, vertical and at the interface – to assess the anisotropy of the build-up and the strength of the interface/Heat Affected Zone induced by the metal deposition. Results show that both processes have limited anisotropy in the conditions studied, even though Cold Metal Transfer presents an important crystallographic and microstructural texture. Depending on the process used and heat treatments applied, the interface/Heat Affected Zone may not be the weakest point of the repaired part despite a neat interface. High temperature creep results also suggest that post weld heat treatments may not be necessary if this is the primary design criteria. Tensile properties of Cold Metal Transfer Waspaloy are highly dependent on the deposit thickness from where the specimens are extracted, due to an in-situ heat treatment that takes place during production of large deposits. The different results are discussed considering the limitations of industrial repair operations such as metal costs, deposition rate, repaired volume and targeted application.
9:20 AM
High Temperature Fatigue Crack Growth in Nickel-based Alloys Refurbished by Additive Manufacturing: Ashok Bhadeliya1; Birgit Rehmer1; Bernard Fedelich1; Torsten Jokisch2; Birgit Skrotzki1; Jürgen Olbricht1; 1Federal Institute for Materials Research and Testing (BAM); 2Siemens Energy Global GmbH & Co. KG
Hybrid additive manufacturing plays a crucial role in the restoration of gas turbine blades, where e.g., the damaged blade tip is reconstructed by the additive manufacturing process on the existing blade made of a parent nickel-based alloy. However, inherent process-related defects in additively manufactured material, along with the interface created between the additively manufactured and the cast base material, impact the fatigue crack growth behavior in bi-material components. This study investigates the fatigue crack growth behavior in bi-material specimens of nickel-based alloys, specifically, additively manufactured STAL15 and cast alloy 247DS. The tests were conducted at 950 °C with stress ratios of 0.1 and -1. Metallographic and fractographic investigations were carried out to understand crack growth mechanisms. The results revealed significant retardation in crack growth at the interface. This study highlights the potential contributions of residual stresses and microstructural differences to the observed crack growth retardation phenomenon, along with the conclusion from an earlier study on the effect of yield strength mismatch on crack growth behavior at a perpendicular interface in bi-material specimens.
9:45 AM
The Effect of a Laser-based Heat Treatment on the Microstructure of a Superalloy After a Minimally Invasive Repair by Direct Energy Deposition: Bernd Muller1; Gerhard Backes2; Wolfgang Kueppers3; Jochen Kittel3; Norbert Pirch3; Susanne Hemes4; Markus Pedersen5; Constantinos Hatzoglou5; Paraskevas Kontis5; 1Rolls-Royce Deutschland Ltd & Co KG; 2Dap RWTH; 3Fraunhofer ILT; 4Access e.V. Aachen; 5NTNU Norwegian University
In this study, a laser-based heat treatment is applied on IN718 superalloy substrate repaired by a minimally invasive direct energy deposition process. The focus is on the laser-based heat treated microstructure, aiming to enable minimally invasive repair processes to take place either “on-wing” or “near-wing”. Hardness measurements were performed on the as-repaired and heat treated microstructure, while electron microscopy, electron backscatter diffraction and atom probe tomography analyses were performed to investigate the microstructure. After the laser-based heat treatment, the hardness of the repaired part increased compared to the as-repaired and reached values similar to that of the substrate. Besides, microstructural analysis unveiled non-uniform γ'' precipitate formation, linked to observed micro-segregation from the repair process persisting post-heat treatment. Precipitation-free areas were observed while co-precipitation of γ'' and γ' in duplet and triplet particles was infrequent. Interdendritic areas exhibited Laves phases regions with needle-shaped δ precipitates forming directly from the Laves phase. Carbonitrides coexisted with Laves phase, creating complex Laves regions. Although a single-step heat treatment will not lead to a complete dissolution of the undesirable microstructure features, a solution treatment step using the same minimally invasive equipment can unlock the full potential of in-situ maintenance through laser-based heat treatments.