Superalloys 2024: General Session 2: Alloy Design/Development II
Program Organizers: Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346

Monday 11:20 AM
September 9, 2024
Room: Exhibit Hall
Location: Seven Springs Mountain Resort

Session Chair: Tresa Pollock, University of California - Santa Barbara; Akane Suzuki, GE Aerospace Research

11:20 AM
Computational Design and Experimental Characterization of a Novel 3rd Generation Single Crystal Superalloy with Balanced High Temperature Creep Strength and Corrosion Resistance: Jeremy Rame¹; Edern Menou²; Didier Locq³; Yohan Cosquer⁴; Amar Saboundji²; Mikael Perrut³; ¹Safran Aircraft Engines, NAAREA; ²Safran Tech; ³DMAS, ONERA, Universite Paris-Saclay; ⁴DGA Techniques aéronautiques
    This paper presents the development of AMS20, a novel third-generation single crystal superalloy designed for the next generation of aeroengines. The alloy design utilizes a computational approach that combines empirical models and CALPHAD calculations to identify compositions meeting targeted specifications. This methodology facilitates the selection of the final AMS20 alloy composition, aiming to optimize high temperature creep properties while preserving excellent high temperature oxidation resistance. The alloy was cast and single crystal bars were grown using the conventional Bridgman method. Subsequently, appropriate solution and aging treatments were developed, and the tensile and creep properties of AMS20 were evaluated. A comparative analysis was performed against reference second and third-generation single crystal superalloys, namely CMSX-4, CMSX-10K, CMSX-4 Plus, and AGAT. Results indicate that AMS20 exhibits a remarkable combination of high temperature creep and oxidation resistance. Specifically, AMS20 demonstrates a creep life at 1200 °C comparable to CMSX-10K alloy, while its cyclic oxidation performance at 1150 °C is akin to second-generation CMSX-4 alloy and notably superior to third-generation reference alloys. However, it is important to note that initial aging results highlight the sensitivity of AMS20 alloy to TCP phases at 1050 °C and its relatively narrow high temperature processing windows. Yet AMS20 remains a promising single crystal superalloy for the future generation of aircraft engines.

11:45 AM
On the Evolution of the γ/γ′ Lattice Misfit and TCP Phase Precipitation in a Highly Alloyed Single Crystalline Ni-base Superalloy: Jakob Bandorf¹; Anna Kirzinger¹; Christopher Zenk¹; Hon Tong Pang²; Catherine Rae²; Howard Stone²; Steffen Neumeier¹; ¹Friedrich-Alexander-Universität Erlangen-Nürnberg; ²University of Cambridge
    Ni-base superalloys of the latest generation are prone to the formation of topologically close-packed (TCP) phases due to their high content of refractory elements. The quantitative correlation between the TCP phase precipitation, the evolution of the lattice parameters, and the γ/γ′ lattice misfit in a highly alloyed single crystal Ni-base superalloy is investigated here. Even in the standard heat-treated state TCP phases are found in the dendrite cores. With additional annealing at 1100 °C further TCP phase precipitation occurs until a constant fraction is reached after 100 h. High-resolution X-ray diffraction experiments conducted at room temperature revealed that the lattice parameter of the γ phase decreases with increasing exposure time and reaches, like the TCP phase fraction, a kind of plateau after long aging durations. In contrast, the lattice parameter of the γ′ phase hardly changes throughout aging, which results in a decrease of the initial γ/γ′ lattice misfit from about -1 % to a plateau of about -0.45 % after 1000 h. Comparison of thermodynamic and lattice parameter calculations with the experimentally determined values revealed that the depletion of the main TCP phase forming elements Re, W and Mo associated with the ongoing TCP phase formation is the main reason for this behavior. It is also shown that the effect of both stress relaxation and TCP phase precipitation results in a reduction of the tetragonal distortion and coherency stresses in the γ matrix channels.

12:10 PM
Combinatorial Materials Research for the Development of New Advanced CoNi-base Superalloys: Lukas Haussmann¹; Steffen Neumeier¹; Andreas Hausmann¹; Enrico Bergamaschi¹; Mathias Goeken¹; ¹Fau Erlangen-Nuernberg
    Nanomechanical testing methods are very well suited to complement combinatorial materials research using diffusion couples. Diffusion couples allow the investigation of the microstructure and the mechanical properties of multiple alloy compositions in a single sample without the need to cast many different alloys. To expand the investigation of mechanical properties on diffusion couples to higher temperatures, indentation creep is a highly suitable technique. In this work, the diffusion couple approach was utilized in combination with a high temperature indentation creep testing technique, using a 25 μm flat punch indenter, to conduct combinatorial investigations on a Co-Ni diffusion couple and on a multinary γ/γ' CoNiCr-base superalloy diffusion couple with increasing Cr content. For the Co-Ni system, the highest room temperature hardness and highest creep resistance at 550 °C was observed between 50 at.% Co to 80 at.% Co. For the γ/γ' CoNiCr-base superalloy CoWAlloy2, an optimum Cr content of 14 at.% has been found. Up to this Cr content the hardness and creep resistance is not altered and the precipitation of undesired phases does not occur. With further increasing Cr content, the γ' volume fraction decreases significantly and undesired W- and Al-rich phases precipitate, leading to an increase in hardness but a deterioration of the creep properties.

12:35 PM
Influence of Re on High-temperature Microstructural Stability and Mechanical Properties of High-Cr CoNi-based Superalloys: Xiaorui Zhang¹; Longfei Li¹; Song Lu¹; Muchun Hou¹; Min Zou¹; Qiang Feng¹; Siliang He¹; ¹University of Science and Technology Beijing
    A multicomponent high-Cr CoNi-based superalloy was developed for potential use in industrial gas turbine materials. In response to the enhanced overall performance of alloys, the microstructural stability and strength of alloys with different Re additions at 950 °C were investigated. During long-term thermal exposure, the ă′ precipitates remained nearly cuboidal and the addition of Re led to a mild decrease in the ă′ volume fraction. The Re addition can effectively reduce the coarsening rate of ă′ precipitates due to both the significant reduction in the effective diffusion coefficient in the ă matrix and the decrease in interfacial energy between the ă and ă′ phases. Despite a reduction in ă′ volume fraction, the addition of Re improved the creep properties of the investigated alloys at 950 °C/200 MPa - 300 MPa. Firstly, the introduction of Re causes the inversion of W partitioning from ă matrix to ă′ precipitates to improve the ă′ strength. And it also elevates the content of Re within the ă phase, thereby enhancing the solid solution strengthening effect. Moreover, this improvement is also attributed to a decrease in the effective diffusion coefficient of the alloy. All these factors contribute to improving the creep properties and yield strength of high-Cr CoNi-based superalloys.