Superalloys 2024: General Session 6: Blade Alloy Processing
Program Organizers: Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346
Tuesday 11:20 AM
September 10, 2024
Room: Exhibit Hall
Location: Seven Springs Mountain Resort
Session Chair: Roger Reed, University of Oxford; Corey O'Connell, Special Metals
11:20 AM
Resistance to Viscoplastic Deformation of Ni-based SX Superalloys with Bimodal Distributions of Gamma-prime Precipitates: Luciana Maria Bortoluci Ormastroni1; Jeremy Rame2; Dominique Eyidi3; Fabio Machado Alves da Fonseca4; Jonathan Cormier5; 1Safran Aircraft Engines; 2NAAREA; 3Institut Pprime/SP2MI ; 4Institut Pprime/Safran Tech; 5Institut Pprime/ENSMA
Ni-based single crystal (SX) superalloys have a well-established history of application in high pressure turbine (HPT) blades and vanes. Nowadays, these components are increasingly being employed in the first stage of the low pressure turbine (LPT). As a result, aircraft engine manufacturers are facing new challenges arising from the design, manufacturing processes, evolving service conditions, and refurbishment requirements. Conventionally, the capability of Ni-based SX superalloys to withstand the harshest environments is related to a homogeneous cuboidal γ/γ microstructure. However, future new applications have considered bimodal γ/γ' microstructures (presence of fine tertiary \947;' precipitates 10-100 nm inside theγγ-channels) resulting from either the manufacturing processes or from the routine use. This study investigates the resistance to the viscoplastic deformation of a 3rd generation Ni-based SX superalloy with a bimodal distribution of γ' precipitates. TEM observations showed presence of dislocations after heat treatment to achieve the bimodal microstructure. Even without plastic strain, dislocations were identified surrounding the secondary γ' precipitates. Stress relaxation and creep properties at 750 °C and 850 °C were very sensitive to such bimodal microstructure. Specimens with a bimodal γ' precipitation showed a creep life five to six times lower than the reference samples. According to the Norton’s type diagram, rate controlling deformation mechanisms of the reference and bimodal microstructures appear to be same at both temperatures and under different initial conditions (with and without prior plastic strain), but with a higher strain rate for the bimodal microstructure.
11:45 AM
Non-destructive Volumetric Methods for Detection of Recrystallized (RX) Grains in Single Crystal (SX) Aerospace Components: Iuliana Cernatescu1; Chris Pelliccione1; Robert Koch1; Ryan Breneman1; Slade Stolz1; Venkat Seetharaman1; David Furrer1; 1Pratt & Whitney
Single-crystal (SX) nickel-based superalloys are used as blade materials for gas turbine aircraft engines due to their superior mechanical and environmental performance. These properties of SX superalloys depend highly upon their crystallographic orientations. The SX superalloy components contain no large angle boundaries, which excludes intergranular oxidation and rupture. However, the industrial manufacturing of SX superalloy blades can still result in the formation of recrystallized (RX) grains which can significantly limit the life of these components. The RX grains can form anywhere within a SX blade but are most frequently observed in areas of high geometrical complexity. These are often areas where high thermal stresses occur during solidification and subsequent cooling processes due to significant mechanical constraint between shell/core materials and airfoil and can occur on the interior walls of hollow configurations. Focused research efforts have been conducted to develop and demonstrate a non-destructive method for volumetric analysis and detection of RX grains in SX components. This method is being further developed and deployed via an integrated computational materials engineering approach to further identify and control critical to quality material and processing parameters to mitigate such features in the most complex production castings. Implementation of this advanced non-destructive evaluation process will be reviewed in terms of targeted locations based on probabilistic material and process modeling.
12:10 PM
Interfacial Strength Evaluation Between Sulfur-segregated Al2O3 and Ni-Al Single Crystal Alloy Using Nanoindentation: Chihiro Tabata1; Toshio Osada2; Takahito Ohmura2; Tadaharu Yokokawa2; Kyoko Kawagishi2; Shinsuke Suzuki1; 1Waseda University; 2National Institute for Materials Science
Ni-base superalloys have excellent oxidation resistance, but impurity S drastically decreases their properties. This is due to the segregation of S to the oxide/substrate interface, but direct and quantitative measurements of the interfacial strength in relation to the S segregation level have not been widely conducted. The objective of this research is to quantitatively analyze the interfacial strength between the Al2O3 layer and Ni-base substrate interfacial strength, depending on the S segregation level, using nanoindentation. Ni-9.8 wt.% Al alloys were prepared by melting the material using either an Al2O3 crucible (high Sinterfacealloy) or a CaO crucible (low Sinterfacealloy). Nanoindentation tests using a 60 degree pyramidal diamond indenter were conducted, and the cross-sections of both specimens exposed the (100) plane. Indentation near the interface formed cracks at the boundary between the two layers, which can be observed as pop-ins in the load-depth curves. The amount of load at the initial pop-in most likely represents the interfacial strength between the Al2O3 layer and Ni-base substrate. A Weibull analysis of results showed that suppression of the S segregation level increased the critical â scale parameter for crack formation by 650 ìN. This suggests that we were able to successfully compare the effect of S segregation on the interfacial strength between the Al2O3 layer and the Ni-base substrate quantitatively
12:35 PM
Effect of Rejuvenation Treatment on SX Ni-based Superalloys Subjected to Low Cycle Fatigue: Inmaculada Lopez Galilea1; Anne Dennstedt2; Sebastian Weber1; Marion Bartsch2; 1Ruhr University Bochum; 2German Aerospace Center
Rejuvenation treatments with integrated hot isostatic pressing have been proven to re-establish the γ/γ' microstructure of single crystalline nickel-based superalloys after creep deformation, close porosity, and recover creep strength to a significant extent. Therefore, rejuvenation treatment is expected to be effective in extending the service life of components such as turbine blades for gas turbines resulting in reduced costs and improved sustainability compared to replacing the component. Since such components are subjected to combined creep-fatigue loading, this investigation is aiming to answer the question if a rejuvenation procedure, which has proved to recover single crystalline superalloys after creep, is effective in rejuvenating these materials after low cycle fatigue. For this purpose, test samples have been subjected after high temperature low cycle fatigue experiments to a rejuvenation procedure. The materials microstructure has been studied by non-destructive X-ray computer tomography before and after rejuvenation. Subsequently, metallographic sections were prepared from rejuvenated samples and investigated by scanning electron microscopy. Pores and precipitates detected in high resolution section images were identified in the reconstructed volume and used to fit the metallographic section images into this volume. Pores and cracks emanating at pores during fatigue testing were closed by rejuvenation as long as they were not connected to the surface. Electron back scatter diffraction performed on the sections revealed that, in contrast to creep samples, the fatigue samples were recrystallized during rejuvenation. It is concluded that fatigue damage cannot be reversed by the same rejuvenation procedure that is effective for creep damage.