Superalloys 2024: General Session 11: Environmental Behavior and Coatings
Program Organizers: Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346
Thursday 8:30 AM
September 12, 2024
Room: Exhibit Hall
Location: Seven Springs Mountain Resort
Session Chair: Ian Edmonds, Rolls-Royce Plc; Patrick Villechaise, CNRS
8:30 AM
Comparison of the Effect of 2 at. % Additions of Nb and Ta on the 1100 °C Oxidation Behavior of Ni - 6Al - (4,6,8) Cr Model Alloys: Rafael Rodriguez De Vecchis1; Rishi Pillai2; Kim Kisslinger3; Meng Li3; Judith Yang3; Brian Gleeson1; 1University of Pittsburgh; 2Oak Ridge National Laboratory; 3Brookhaven National Laboratory
To continue improving alloy performance in harsh service environments, the development of alumina-forming nickel-based superalloys is essential. Current generations of these alloys heavily rely on the addition of refractory elements to enhance their mechanical properties at high temperatures; however, a systematic understanding of how such additions affect the overall oxidation behavior is still not well established, particularly from the standpoint of predicting the transition from internal to external alumina formation. The present work seeks to better understand the intrinsic effects that common minor additions of Ta and Nb have on the oxidation behavior of alumina-scale forming γ-Ni model alloys. By combining a novel simulation approach with high-temperature oxidation experiments and advanced characterization techniques, the present study provides insightful details on the differing effects that 2 at. % addition of Ta and Nb have on the alumina-scale formation of Ni-based alloys during 1100 °C oxidation.
8:55 AM
Fatigue Durability of a Single Crystal Nickel-based Superalloy with Prior Corrosion: A. Martin1; E. Drouelle1; J. Rame2; Fernando Pedraza3; J. Cormier4; 1Safran Aircraft Engines; 2NAAREA; 3Universite de La Rochelle; 4Institut Pprime
The impact of hot corrosion on the low-cycle fatigue (LCF) life of the AM1 Ni-based single-crystal (SX) superalloy in as-cast (AC) and fully heat-treated (FHT) states has been studied. Microstructural features such as pores and chemical segregation have a significant impact on LCF fatigue strength at 950 °C. Surface pores act as stress concentration zones, influencing crack initiation and propagation. The reduction in the chemical dendritic segregation through solution heat treatment improves the LCF resistance. Pre-corrosion lowers the LCF lives by increasing stress concentration and facilitating multiple crack initiations with a brittle, spalled corrosion layer on the surface. The mechanical degradation occurs simultaneously to hot corrosion and oxidation, the latter being influenced by the distance from the layer undergoing hot corrosion. Heat treatment still appears to be a positive factor in improving the service life of AM1.
9:20 AM
Influence of the Coating Brittleness on the Thermomechanical Fatigue Behavior of a β-NiAl Coated R125 Ni-based Superalloy: Capucine Billard1; Damien Texier2; Matthieu Rambaudon1; Jean-christophe Teissedre1; Dimitri Marquie3; Lionel Marcin3; Hugo Singer3; Noureddine Bourhila3; Vincent Maurel1; 1Mines Paris - PSL University; 2ICA Mines Albi; 3SAE
The brittleness of an aluminide diffusion coating protecting a Ren´e 125 Ni-based polycrystalline superalloy was investigated over a wide range of temperatures in its as-received and thermally aged form. Isothermal and thermal cycled aging were performed on the coated system at a maximum temperature of 1100 °C. Microstructure evolutions and damage initiation within the coating were characterized. Interrupted tensile tests and thermomechanical fatigue tests were conducted to document critical stress-strain conditions leading to the coating cracking and lifetime for the case of thermo-mechanical fatigue loading. Advanced digital image correlation and acoustic emission techniques were used to detect coating cracking. Isothermal oxidation or cyclic oxidation led to improved strain-to-failure due to metallurgical evolutions and also longer fatigue life under thermomechanical fatigue conditions.
9:45 AM
Very High Cycle Fatigue Properties of a Coated Nickel-based Single Crystal Superalloy: Antonio Vicente Morales1; Florent Mauget2; Amélie Caradec2; Baptiste Larrouy3; Patrick Villechaise2; Jonathan Cormier2; 1Safran Helicopter Engines and Institut Pprime; 2Institut Pprime; 3Safran Helicopter Engines
Very High Cycle Fatigue (VHCF) properties of thermally sprayed MCrAlY coated samples of CMSX-4 at high temperature were studied. Nine fatigue tests up to failure were performed at 1000 °C, 20 kHz and R = -1 on coated samples. These samples showed lower fatigue life when compared with the bare reference. Fatal crack initiation systematically occurred at the interdiffusion zone (IDZ) between the coating and the CMSX-4 substrate or at a casting pore in the vicinity of the IDZ. Failed samples showed a high density of secondary surface cracks. In order to better understand the mechanism leading to surface cracking, one interrupted test was performed. It is shown that cracks nucleated from the very first fatigue cycles and propagated through the coating almost instantly. Surface cracks then spent most of the fatigue lifetime sitting at the IDZ/substrate interface. The fatal as well as the surface crack initiation mechanisms are discussed to better understand the durability in these VHCF conditions.