Superalloys 2021: Wednesday Interactive Session on Blade Alloy Behavior
Program Organizers: Sammy Tin, University of Arizona; Christopher O'Brien, ATI Specialty Materials; Justin Clews, Pratt & Whitney; Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346; Qiang Feng, University of Science and Technology Beijing; Mark Hardy, Rolls-Royce Plc; John Marcin, Collins Aerospace; Akane Suzuki, GE Aerospace Research
Wednesday 10:10 AM
September 15, 2021
Room: Poster Area
Location: Virtual Event
Measurement and Evaluation of Co-existing Crack Propagation in Single Crystal Superalloys in Hot Corrosion Fatigue Environments: Laurie Brooking1; Julian Mason-Flucke2; Grant Gibson2; Jonathan Leggett2; Iain Palmer1; John Nicholls3; Simon Gray3; 1Frazer-Nash Consultancy Ltd; 2Rolls-Royce plc; 3Cranfield University
Gas turbines blades are required to operate at high temperatures whilst being subjected to stress and corrosive environments. These demanding conditions have led to the need to better understand the interactions between corrosion and loading in order to improve lifing algorithms used for service interval predictions. A new crack growth measurement technique involving direct current potential difference (PD) has been developed for use in these harsh conditions. A good correlation between PD signal and crack area has been achieved. Estimations of the crack depth have been made based on fracture surface imaging, these experimentally measured crack depth propagation rates have been compared with Paris law predictions. A stress intensity factor (SIF) interaction between multiple cracks was found, where the SIF is enhanced when cracks become close. It was found that both the fatigue cycle rate and the crack shape appear to influence the SIF magnitude and the crack depth at which specimens fail, or initiate into crack propagation which is consistent with fatigue.
Understanding the Effects of Alloy Chemistry and Microstructure on the Stress Relaxation Behavior of Ni-base Superalloys: Linhan Li1; Joshua McCarley1; Eugene Sun2; Sammy Tin3; 1Illinois Institute of Technology; 2Formerly of Rolls-Royce Corporation; 3University of Arizona
The stress relaxation behavior of two experimental and one commercial powder processed Ni-base were assessed using a servo-hydraulic frame under strain control at 700 ˚C. In addition to quantifying the effect of composition on the stress relaxation behavior, the effect of microstructure and initial strain were also evaluated. The magnitude and rate of stress reduction for the various samples was measured during testing and an apparent activation model was used to normalize the magnitude of the stress drop with the initial stress. Stress relaxation tests with an initial strain of 0.6 % exhibited characteristic behaviors that could be correlated to alloy chemistry and microstructure. The extent of stress relaxation in highly alloyed RRHT5P samples possessing high volume fractions and a high number density of intragranular ã′ precipitates was limited. Although P additions were not observed to exert any significant effect, processing of these alloys with lower cooling rates from solution to coarsen the ã′ precipitates was shown to effectively increase the degree of stress relaxation. Reducing the degree of alloying and maintaining a lower overall fraction of ã′ precipitates effectively confers a higher degree of stress relaxation at 700 ˚C. Stress relaxation testing and the application of an apparent activation volume model may be effectively used for characterizing the notch sensitivity and crack growth behavior of high temperature structural materials.
HIP +ITF of SS-PREP® Superalloy Powder: Qu Zonghong1; 1Sino-Euro Materials Technologies of Xi'an Co., Ltd
The HIP (Hot Isostatic Pressing) + ITF (IsoThermal Forging) process was carried out for SS-PREP® (Super Speed Plasma Rotating Electrode Process) powder of nickel-based superalloy FGH4097. Powder made via SS-PREP® shows fine and uniform particle size, high sphericity and purity. The HIPed compact has good hot workability during isothermal forging to obtain refined grains. The heat treatment tests were performed at different solution temperatures, and mechanical properties were measured. Compared with the established as-HIP process, SS-PREP®+HIP+ITF with 1180 ℃ solution heat treatment resulted in higher strength, ductility and LCF (Low Cycle Fatigue) life, with acceptable increase in accumulated creep strain.
Laboratory-scale Replication of Deposit-induced Degradation of High-temperature Turbine Components: Matthew Kovalchuk1; Brian Gleeson1; 1University of Pittsburgh
This study investigated the linkages between deposit chemistry and degradation morphology of field-exposed aero-turbine parts and the associated development of effective lab-scale replication testing procedures. Inductively coupled plasma-optimal emission spectroscopy (ICP-OES) analysis indicated that the water-soluble deposit constituents were mainly Na-rich, Ca-rich or a mix of these, with the relative amounts having a dependence on geographic region in which a given part was mainly exposed. Degradation of the field-exposed parts was characterized using scanning electron microscopy (SEM) and revealed unconventional hot corrosion attack. Microstructures included duplex oxide scales, Ca-containing oxide, internal oxidation, sulfidation, and nitridation. Degradation mechanisms elucidated by replication testing were deposit-induced selective depletions at high-temperature and low-temperature oxidation. Field degradation was replicated when considering the thermal dependences of both stages. Replication of a chromide-coated field part required calcium chromate liquid formation during high-temperature testing. Electron probe microanalysis (EPMA) of the coating subsurface revealed extensive Cr depletion after exposure to CaO above the calcium chromate eutectic temperature. Oxidation temperature also contributed to replicating field degradation microstructures. Specifically, matching degradation was observed after the depleted superalloy or chromide coating was oxidized in air at an intermediate temperature.
Strengthening Mechanisms of Ni-Co-Cr Alloys via Nanotwins and Nanophases: Bin Gan1; Ji Gu2; Miguel Monclus3; Xue Dong4; Yunsong Zhao5; Hongyao Yu1; Jinhui Du1; Min Song2; Zhongnan Bi1; 1Central Iron and Steel Research Institute; 2Central South University; 3IMDEA Materials Institute; 4University of Science and Technology Beijing; 5Beijing Institute of Aeronautical Materials
The ultra-high strength of multiphase (MP) alloys for fastener applications is endowed by cold deformation, which induces deformation twinning or phase transformation in the materials. In the present work, MP159 alloy as well as NiCoCr medium entropy alloy are investigated to assess the effectiveness of a torsional pre-straining as well as surface mechanical grinding treatments to further improve their strength. For the pre-torsion route, microstructural analysis shows that with the activation of different twinning systems and stacking faults, the sequential torsion and tension tests lead to the observed hierarchical microstructure, which gives rise to the significant increase in the yield strength in the investigated alloys while retaining a good ductility. Further studies reveal that aging treatment of the pre-torsion bars provides additional strengthening to MP159 alloys, with the synergistic strengthening of nanotwins and nano-precipitates. After the surface mechanical grinding treatment of NiCoCr alloys, a nanocrystalline structure is formed in a region extending about 150 mm from the edge. Considering the high applied strains, a high density of deformation twins is expected in the nanocrystalline region. Micropillar compression of single crystal and nanocrystalline NiCoCr alloy shows that with the refinement of grain size from 200 mm to 40 nm, the yield strength could increase from 900 MPa to 2500 MPa. This reveals that the refinement of grain sizes can significantly increase the yield strength of NiCoCr alloys with a low stacking fault energy.
A New Approach to Strength Prediction of Ni-Base Disc Superalloys with Dual Phase γ/γ': Liberty Wu1; Toshio Osada1; Ikumu Watanabe1; Tadaharu Yokokawa1; Toshiharu Kobayashi1; Kyoko Kawagishi1; 1National Institute for Materials Science
Previously reported strength prediction models for polycrystalline Ni-base superalloys tend to underestimate the overall strength. This is primarily due to neglecting the rule of mixtures for hardening by g/g’ and inaccurate estimation of other strengthening factors such as solid solution hardening of g matrix and grain boundary strengthening, etc. To address these issues, a series of single-crystal tie-line modeling alloys with g’ size suitable for validating the strong pair-coupling and Orowan looping mechanisms were prepared, in an attempt to develop more reliable g’ hardening models. Critical resolved shear stress values were measured on these modeling alloys at 650 ºC using compression tests, which allowed the distinction between strength contribution from rule of mixture and interfacial strength. Compared with the experimentally obtained interfacial strengths, the predicted results by classical models could not reflect the strength increment expected at higher g’ volume fraction. Hence, a modified version of the classical equations has been proposed here for improved predictability.
On Optimising Ring-rolling Manufacturability of C&W Nickel Superalloys for Aero-engine Turbine Disk: Fauzan Adziman1; Ryosuke Takai2; Yuanbo Tang1; Shigehiro Ishikawa2; Daniel Barba Cancho1; Enrique Alabort Martinez1; Andre Nemeth1; Naoya Kanno2; Roger Reed1; 1University of Oxford; 2IHI Corporation
Ring-rolling has proven notoriously difficult to model, control and optimise accurately. We have studied a multi-objective optimisation involving (1) process parameters, (2) geometrical design, and (3) alloy design for manufacturability of a newly developed M647 gamma-prime strengthened C&W nickel superalloy suitable for aero-engine turbine disk. Accurate computational models based on accurate experimentation which allow for knowledge-based choice of the manufacturing variables, built to mitigate the occurrence of excessive adiabatic heating and crack nucleation sites, represent an important step towards the sought-after optimised ring-rolling manufacturability. The results indicate a major improvement of ring-rolling manufacturability by cutting more than 80 percent of processing time whilst maintaining crack-free condition.
Crystal Plasticity Model for Nickel-based Superalloy René 88DT at Elevated Temperature: Monica Soare1; Shenyan Huang1; Mallikarjun Karadge1; 1GE Global Research
A micro-structurally informed crystal plasticity model was developed for polycrystalline alloy René 88DT (R88DT) at a high temperature (650 oC). R88DT is a precipitation strengthened Ni-based superalloy used in gas turbine engine disks due to high tensile strength, superior creep resistance, and high resistance to fatigue crack growth. It was experimentally observed [1] that crack initiation in polycrystalline superalloys is highly dependent on the grain size, orientation and microstructure, as well as on the inelastic sub-grain properties. Thus, understanding the fundamental deformation mechanisms at the sub-grain level is a necessary step for development of fatigue life models. For this purpose, single crystals with microstructures representative of R88DT were first created by the investment casting process. Specific crystallographic orientations were mechanically tested in tension and compression to investigate dominant deformation mechanisms as activation of various slip systems, stacking faults/micro twin formation and precipitate shearing. These mechanisms were incorporated into a physics - based viscoplastic constitutive model. The model was calibrated using data from tests on single crystals and it was then applied for each grain in polycrystalline R88DT to predict the macroscopic stress-strain response as well as heterogeneous local stress and strain fields.
Recent Progress in Local Characterization of Damage Evolution in Thermal Barrier Coating under Thermal Cycling: Vincent Maurel1; Vincent Guipont1; Lara Mahfouz1; Basile Marchand1; Alain Köster1; Anne Dennstedt2; Marion Bartsch2; Fabrice Gaslain1; Florent Coudon3; 1Mines Paris - PSL University; 2DLR Koln; 3SAFRAN
Thermal barrier coating (TBC) systems are currently often tested by thermal cycling with or without temperature gradient on cylinder coupons. As a major drawback, edge effect associated with this geometry induces large scatter in TBC life at spallation. Thus, we promote the use of a laser shock to induce an artificial defect located at the top-coat/oxide interface. This method enables firstly to monitor damage evolution by means of non-destructive methods from this defect during thermal cycling at homogeneous temperature and for burner rig testing with superposed thermal gradient across the TBC. Secondly, by the knowledge of artificial defect location, an accurate 3D reconstruction of the crack tip was performed based on serial sectioning by focus ion beam and viewing by scanning electron microscopy. Founded on these observations, a sensitivity analysis of the measurement uncertainties with respect to the energy release rate of propagating cracks and to the process zone where damage elaborates is proposed.
Assessment of Mechanical and Metallurgical Features of Inconel 680 Weld Metal: Rafaella Silva1; Emerson Miná1; Ricardo Marinho1; Giovani Dalpiaz1; Marcelo Piza Paes1; Marcelo Motta1; Cleiton Silva1; Hélio Miranda1; 1Universidade Federal do Ceará
The present study assessed the mechanical properties and metallurgical features of a new solid-solution Ni-based alloy called Inconel 680, which has been developed for high strength applications, including dissimilar welding for high strength steels. Steel plates were buttered with Inconel 680, to prevent any dilution with the steel. In sequence, the buttered steel plates were joined. Samples from the test plates were extracted for chemical composition analysis, metallography preparation, uniaxial tensile testing, and hardness and microhardness evaluations. Microstructural characterization was performed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results of the mechanical properties showed that the Inconel 680 alloy filler metal provides an excellent mechanical strength, including a high yield strength, with an average value superior to 600 MPa, and good ductility, reaching an elongation of at least 40%. In addition, this study provides valuable insight into the microstructure of the Inconel 680 alloy. The overall evaluation indicated that this filler metal is an excellent option for many dissimilar welding applications, such as API 5L X65 pipes internally cladded with Inconel 625.
High-throughput Approaches to Establish Quantitative Process-structure-property Correlations in Ni-base Superalloy: Nishan Senanayake1; Semanti Mukhopadhyay2; Jennifer Carter1; 1Case Western Reserve University; 2The Ohio State University
A high-throughput approach for collecting microstructure and mechanical properties was developed to model the process-structure-property (PSP) correlations in polycrystalline Ni-based superalloy ME3. The semi-automated image processing algorithm captured the area fraction and size distribution of secondary and tertiary ã′ particles from scanning electron microscopy (SEM) images of polished samples. The yield strength and elastic modulus were calculated with an automated algorithm using load-time-displacement data generated by microindentation. Thirty heat treatments were conducted to create various ã′ distributions which are the primary strengthening mechanism of Ni-based superalloys. The PSP correlations among the predictor and response variables were evaluated with regression models and validated with adj-R2 and residual standard error statistics. The PSP statistical models built by using high-throughput protocols align with the previous statistical and theoretical models.
The Influence of Hot Corrosion Damage on the Low Cycle Fatigue Fracture Modes of a Disk Superalloy: Jeremy Hart1; Michael Task1; Mario Bochiechio1; 1Pratt & Whitney
Fatigue cracking of nickel disk superalloy fatigue specimens subjected to hot corrosion exposures prior to and during fatigue testing at 704 °C has been investigated. Pre-corroded notched fatigue specimens were exposed to a mixture of sulfates at 677 °C prior to fatigue testing, while in situ treated specimens were only exposed to the sulfate mixture during the elevated temperature fatigue test. Both the pre-corroded and in situ corrosion treatments resulted in a significant reduction in fatigue life compared to uncorroded specimens tested at the same temperature and stress conditions. Investigation of fracture surfaces by scanning electron microscopy and electron microprobe equipped with an energy dispersive spectrometer allowed for determination of fatigue crack initiation sites, as well as morphological and chemical evaluation of the alloy microstructure damaged by hot corrosion. Fatigue crack initiations originated from pit features and microstructural degradation caused by hot corrosion. For pre-corroded specimens, cracks initiated along grain boundaries near the pit depth and propagated intergranularly into the alloy. For in situ treated specimens, cracks formed near the surface oxide above growing pits and propagated into the pit as it grew, eventually propagating in a transgranular nature further into the alloy. Sulfur-rich precipitates were detected along grain boundaries below the hot corrosion pits of both pre-corroded and in situ treated specimens. Sulfur was also detected along crack surfaces and grain boundaries that were 50-100 ìm below crack initiation sites in the in situ treated specimens.