Superalloys 2024: Interactive Session A: Alloy Design/Development
Program Organizers: Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346
Monday 10:10 AM
September 9, 2024
Room: Winterberry
Location: Seven Springs Mountain Resort
A-1: A Novel Wrought Ni-based Superalloy with High-temperature Strength, Resistance to Creep Rupture and Resistance to Oxidation: Matthew Bender1; Rafael Rodriguez De Vecchis1; Joseph Jankowski1; 1ATI
ATI 273™ alloy was developed to be a fabricable, creep-resistant, and oxidation-resistant superalloy. This paper summarizes material characterization of early vacuum-melted lab heats focusing primarily on its oxidation resistance, though high-temperature strength properties will also be addressed. Short- and long-term continuous isothermal exposure data for 871 and 982 °C testing in dry air will be presented with an emphasis on understanding the impact of Ta addition on scale formation. Furthermore, cyclic exposure testing in flowing air was carried out to assess oxide scale adhesion and healing. ATI 273 has an intentional tantalum addition of 2.5 wt. %, and this impactful element increases the alloy’s resistance to both oxidation and creep. This paper will show the alloy’s improved properties are linked to Ta addition and Ti reduction in the chemistry leading to improved properties compared to ATI 263™ and Haynes® 282® alloys. ATI 273 is being considered for high temperature structural applications, especially those for land-based gas turbine and aerospace engines.
A-2: Accelerating Alloy Development for Additive Manufacturing: Elisabeth Kammermeier1; Julius Weidinger1; Illya Ionov1; Markus Ramsperger2; Benjamin Wahlmann1; Carolin Körner1; Christopher Zenk1; 1Fau Erlangen-Nuernberg, Wtm; 2GE Additive
Additive Manufacturing (AM) is revolutionizing the production of complex superalloy parts, yet its advancement is hindered by the high costs and extensive time required for atomizing powders from which new alloys are produced and tested. This study presents our approach to expedite and economize alloy development for AM. At the heart of this method is the CALPHAD-based multi-criteria optimization algorithm PyMultOpt, utilized for selecting potential alloys, which are then produced through arc-melting. Our innovative testing framework involves two key processes: (i) assessing alloy processability via electron beam remelting of bulk material, and (ii) evaluating mechanical properties after refining coarse-grained material via deformation and recrystallization. Focusing on Alloy 247 and derivatives selected through PyMultOpt, our approach successfully emulates AM-like microstructures in arc-melted material. The compressive creep tests on the recrystallized microstructure of Alloy 247 indicate a minimal creep rate comparable to that of AM specimens. Moreover, profilometry-based indentation plastometry tests at 760 °C offer a rapid, high-temperature evaluation method, allowing for preliminary alloy ranking before extensive creep testing. This study demonstrates that remelting and recrystallization of bulk material can reproduce AM-like microstructures, enabling a faster and more cost-effective assessment and ranking of new alloys in terms of their mechanical properties and AM-processability, as opposed to the traditional, powder-dependent alloy development methods.
A-3: Composition and Heat Treatment Modifications of a New Low-cost Ni Base Wrought Alloy for Improved Creep Resistance and Elevated Temperature Ductility: Ning Zhou1; Filip Van Weereld1; Gian Colombo1; Mario Epler1; 1Carpenter Technology Corporation
Exp-G27 is a new low-cost Ni base wrought alloy developed by Carpenter Technology Corporation for applications such as jet engine turbine casing and internal combustion engine exhaust valves. Mainly strengthened by ã’, Exp-G27 has higher temperature stability compared to alloy 718. Within the targeted service temperature range between 704 °C to 871 °C, Exp-G27 demonstrates comparable mechanical performance as Waspaloy but with a significantly lower raw material cost. However, the creep and stress rupture of Exp-G27 is slightly lower than Waspaloy. In this study, a cost-performance tradeoff study was carried out to help make modification to the original Exp-G27 to achieve superior creep/stress rupture performance than Waspaloy while still being cost competitive.
A-4: Development of a New Low-cost Polycrystalline Nickel-base Superalloy: George Wise1; Hon Tong Pang1; Paul Mignanelli2; Mark Hardy2; Nicholas Jones1; Howard Stone1; 1University of Cambridge; 2Rolls-Royce plc
There is significant industrial demand for low-cost polycrystalline Ni-base superalloys that can be utilised for rotating and static applications at intermediate temperatures in aircraft engines. In this work, we report on the microstructure, heat treatment response, mechanical properties and oxidation behaviour of a newly developed alloy for these applications.The alloy has been designed to improve on the thermal stability and mechanical performance of Inconel718 (IN718), whilst offering lower processing costs than advanced cast & wrought alloys such as Alloy 720Li and Renè 65. The study highlights key areas of alloy development, comparing the alloy properties where possible to current commercially available alternatives.
A-5: Development of Novel Ni-Co Base P/M Disk Superalloy by Redesigning Based on Turbine Blade Alloy, TM-47: Toshio Osada1; Makoto Osawa1; Yuhi Mori1; Ayako Ikeda1; Hiroshi Harada1; Takuma Kohata1; Kyoko Kawagishi1; 1National Institute for Materials Science
The temperature capability of current state-of-the-art high-pressure disk superalloys is around 700°C. To further improve their temperature capabilities, new disk alloy design approaches with a focus on blade alloy compositions, which was designed for applications at temperatures of above 900°C or higher, may be effective. In this study, novel Ni-Co base disk superalloys were designed based on a combination of Ni-base blade superalloy TM-47 and Co-12.5wt.% Ti, both of which possess a γ-γʹ two-phase structure. First screen results using single crystal casts revealed TM-47 to be a potentially promising candidate as a base alloy for Ni-Co base disk superalloy, while additions of Co-12.5 wt.% Ti to TM-47 was found to improve creep strength of the alloy. A later investigation using P/M alloys revealed that limited additions of Co-12.5wt.% Ti to the base alloy also improves powder manufacturability, phase stability, and high temperature proof stress. Thus, TM-47 M2 (20 wt.% addition of Co-12.5wt.% Ti to TM-47) was selected as a candidate alloy for subscale manufacturing trial. Creep tests at 760 °C/630MPa demonstrated that the selected TM-47 M2 provides superior creep properties compared to other conventional disk superalloys, especially for the 0.2 % creep time, which is a critical property for high pressure turbine disks.
A-6: Effect of the Interfacial Strain Anisotropy on the Raft Structure of Ni-base Single Crystal Superalloys and Novel Alloy Design Approach by Controlling the Lattice Misfit and the Elastic Misfit: Takuma Saito1; Hiroshi Harada1; Tadaharu Yokokawa1; Makoto Osawa1; Kyoko Kawagishi1; Shisuke Suzuki2; 1National Institute for Materials Science; 2Waseda University
Enhancing the aspect ratio of the γ′ precipitates in the raft structure of Ni-base single crystal superalloys for high-pressure turbine blades is a fundamental approach to improve the creep resistance at higher temperature and lower stress conditions. To obtain larger aspect ratio, the alloy design strategy to enlarge the lattice misfit between γ and γ′ phases towards negatively larger side has been applied. However, the fundamental driving force for the raft structure formation, “interfacial strain anisotropy”, has been ignored for the alloy design. Here, interfacial strain anisotropy is a difference of the interfacial strain between horizontal and vertical γ/γ′ interface, and this is caused by the interaction of loading stress with the elastic misfit between γ and γ′ phases. In this study, model alloys imply that the aspect ratio is modulated by kinetic factor caused by Re with a presence of interfacial strain anisotropy.
A-7: Effects of Zirconium Additions on the Microstructure and Stress-rupture Properties in Polycrystalline Ni-base Superalloys: Yang Zhou1; Yanna Cui1; Bo Wang1; Jiamiao Liang1; Shuping Li1; Jun Wang1; 1Shanghai Jiao Tong University
In present work, comprehensive investigations were conducted to examine the distribution behavior of the minor alloying element Zr, its impact on microstructural evolution and effect on the high-temperature stress-rupture properties in IN 100 superalloys. The results indicate that the presence of Zr influences the eutectic phase in as-cast alloys, resulting in a reduction in the ã channel width and an increase in both the volume fraction and size of the ã' phase. Through time of flight-secondary ion mass spectrometry and transmission electron microscope analysis, Zr is found to segregate along the eutectic front in the form of Ni5Zr in 900 °C stress-ruptured samples, rendering IN 100 alloys enhanced creep resistance at elevated temperatures. Heat treatment at 1200 °C could effectively eliminate the eutectic structure, thus mitigating the segregation of Zr. A maximum endurance life in IN 100 alloys at 900 °/314 MPa and 950 °/225 MPa is reached when Zr content is approximately 700 ppm. Synergistic effects including the eutectic content, volume fraction and the degree of rafting of the ã' phase together with the dislocation network structure were analyzed and discussed, contributing to the improved stress-rupture properties in IN 100 alloys.
A-9: Freckle Formation Propensity Criterion for New Superalloy Design: Adarsh Shukla1; Richard DiDomizio2; Andrey Meshkov2; Timothy Hanlon2; Daniel Cody2; 1GE Aerospace Research, India; 2GE Aerospace Research, USA
Freckles are casting anomalies generally detrimental to the mechanical properties of superalloys. This work presents a new freckle formation propensity criterion calculated using only alloy composition to rank the freckle propensity of alloys when processed via the same melting route at common conditions This is achieved by combining literature established changes in density of solidifying liquid (ρ/ρ) with an approximation for permeability within the mushy zone, using enthalpy of fusion and solidification range of the alloy. Also, a methodology to calculate ρ/ρ using electron probe microanalysis (EPMA) on as-cast coupons of superalloys is outlined. Additional factors influencing the permeability within the mushy zone, such as the presence of primary carbides, can also be calculated based on alloy chemistry, and incorporated to refine the freckle formation propensity criterion.
A-10: Microstructural and Thermomechanical Assessment of Computationally Designed Ni-based SX Superalloys: Abel Rapetti1; Alice Cervellon1; Edern Menou2; Jérémy Rame3; Franck Tancret4; Jonathan Cormier1; Paraskevas Kontis5; 1Institut Pprime Upr Cnrs 3346; 2Safran Tech; 3Safran Aircraft Engines; 4Institut des Matériaux Jean Rouxel - UMR 6502; 5Norwegian University of Science and Technology
Five computationally designed single crystal superalloys have been developed for aircraft engine airfoils submitted to high temperatures. The broad steps of the alloy design procedure are presented in this study. Tensile and creep properties of these SX superalloys are evaluated in regard to the predictions of the creep-life model and/or in regard with reference SX superalloys. Effective and predicted density show a good consistence. The ã' phase fraction predicted by CALPHAD calculations at the design stage and the ones evaluated in this work are consistent as well. For AMSP2 alloy, atom probe tomography measurements were conducted. We observe that excessive additions of rhenium to a platinum containing SX superalloy have a strong impact on creep properties, reducing the creep lifetime compared to the reference alloy TROPEA, and strongly affect the ã/ã' coherency, leading to the absence of rafting at intermediate temperatures (950 °C – 1050 °C).
A-11: Principle for Homogenization Design of High-generation Single Crystals Superalloys Containing Increased Refractory Contents: Wanshun Xia1; Xinbao Zhao1; Quanzhao Yue1; Yuefeng Gu1; Ze Zhang1; 1Zhejiang University
Increasing the fractions of certain refractory elements resulted in the development of modern single-crystal superalloys with improved high-temperature performance, but also increased solidification segregation of elements. The importance of solution treatment to reduce segregation and homogenize the microstructure has been well verified; however, guidelines for achieving simple but effective homogenization practices have yet to be developed. In this study, the effects of different solution treatments on the creep properties of a fourth-generation single-crystal superalloy were investigated, and two guidelines for designing homogenization practices for modern single-crystal superalloys were proposed. First, the degree of homogenization achieved by solution treatment will be saturated once the dendritic segregation coefficient of specific elements reaches a certain limit (lower than 1.2 for Re and W, and higher than 0.9 for Al and Ta). Second, if the residual segregation is strong, different degrees of local deformations between the dendrite core (D) and interdendritic (ID) regions induce uneven fractures in the alloy. An effective, fully homogenized structure should exhibit similar local strengths in the D and ID regions. These guidelines will help assess the effectiveness of solution treatments and guide the development of new solution treatment strategies for modern single-crystal superalloys.