Superalloy 718 and Derivatives: Welding, Manufacturing & Repair
Program Organizers: Joel Andersson, University West; Chantal Sudbrack, National Energy Technology Laboratory; Eric Ott, GE Additive; Zhongnan Bi, Central Iron and Steel Research Institute
Wednesday 10:15 AM
May 17, 2023
Room: Admiral
Location: Sheraton Pittsburgh Hotel at Station Square
Session Chair: Joel Andersson, University West; Daisuke Nagahama, Honda R&D Co Ltd
10:15 AM Invited
Tensile Properties of Inconel 718 Produced by LMD-Wire: Jonathan Cormier1; Sandra Cabeza2; Guillaume Burlot1; Romain Bordas1; Mélanie Bordas-Czaplicki1; Fabio Machado Alves da Fonseca1; Stefan Polenz3; Franz Marquardt3; Elena Lopez3; Patrick Villechaise1; 1ENSMA - Institut Pprime - UPR CNRS 3346; 2Institut Laüe Langevin (ILL); 3Fraunhofer IWS
The anisotropy in tensile properties of Wire Laser Metal Deposited Inconel 718 has been investigated from room temperature up to 850°C at a strain rate of 5.0 10-4 s-1. These properties have been investigated along, at 45 degrees and perpendicular to the building direction. Moreover, different heat treatments have been used: as-built, solution treated to dissolve Laves phases, solution treated + aged to trigger γ′/γ′′ precipitation and direct-aged. According to this extensive characterization of tensile properties, complemented by SEM, EDS and EBSD characterizations, it is shown that, whatever the temperature, Yield stress and tensile resistance have a very weak anisotropy and that tensile properties are mostly dependent to the prior heat treatment state. The anisotropy is only observed on elastic properties, due to a pronounced crystallographic texture inherited from the directional thermal gradient during the building process. Moreover, Laves phases do not seem to have a strong impact on tensile properties for this coarse grain material. The relative contributions of γ′/γ′′ precipitation, grain size, stored “processing” dislocations to tensile properties will be analyzed on the light of comparisons with C&W processed Inconel 718.
10:45 AM
Microstructural and Tensile Properties Evolutions of Direct-aged Waspaloy Produced by Wire Arc Additive Manufacturing: Marjolaine Sazerat1; Azdine Nait-Ali1; Lucie Barot2; Alice Cervellon2; Inmaculada Lopez-Galilea3; Dominique Eyidi1; Anne Joulain1; Patrick Villechaise1; Jonathan Cormier1; Sebastian Weber3; Roland Fortunier4; 1Institut Pprime; 2Safran Aircraft Engines; 3Ruhr University Bochum; 4LTDS
The microstructure and tensile properties of direct aged Waspaloy manufactured using wire arc-based Cold Metal Transfer (CMT) have been investigated. Samples were exposed to temperatures ranging from 700°C to 900°C, for up to 96 hours. In the as-deposited condition, pronounced chemical segregation is inherited from the process, leading to heterogeneous γ' precipitation between dendrite cores and interdendritic spacings. Precipitate size and distribution were measured in both areas for each heat treatment, and a diffusion-controlled coarsening behavior following the LSW theory was observed for temperatures above 760 °C. Activation energies were calculated. Tensile tests at room temperature were carried out on the additive alloy pre- and post-aging, but also on wrought sub-solvus and super-solvus treated material for reference. Results showed that heat treatment significantly increased the yield strength and ultimate tensile strength of the CMT samples, of up to +340 MPa compared to the as-built conditions. Elongation, however, decreased from 40-45% to 16-28%. Direct aged CMT Waspaloy exhibited a similar behavior to that of wrought super-solvus Waspaloy, due to their large grains (~200-250 µm). Anisotropy in tensile properties was estimated by calculating the ratio of properties for horizontal and vertical specimens. Finally, the formation of secondary phases was assessed. Thermodynamic calculations predicted the formation of M23C6, η and σ in interdendritic spacings at thermodynamic equilibrium. By using Electron diffraction patterns and Energy-Dispersive X-ray Spectroscopy in TEM, intergranular (Cr,Mo)23C6 secondary carbides decorating grain boundaries and near (Ti,Mo)C primary carbides in the interdendritic spacings were observed to nucleate and grow.
11:05 AM
IN718 Cold Gas Repair Spray of Large Cavities – Microstructure and Residual Stresses: Florian Lang1; Johannes-Christian Schmitt2; Sandra Cabeza3; Thilo Pirling3; Jochen Fiebig2; Robert Vaßen2; Jens Gibmeier1; 1Karlsruhe Institute of Technology; 2Forschungszentrum Jülich GmbH; 3Institut Laue-Langevin
Cold spraying is an established process for coating substrates with similar or dissimilar materials. By use of a high-pressure process gas stream, solid particles are accelerated onto a substrate at high velocities. The method is particularly suited for repair applications, since neither structural changes nor oxidation occur during the process. Furthermore, cold spray coating usually induces compressive residual stresses in the coating system that positively influence the fatigue behaviour.To investigate the suitability of the cold spray process for repairing large cavities in Inconel 718 components, sample geometries were manufactured, containing tapered cavities with a depth of 4 mm. The cavities were filled with Inconel 718 particle by cold gas spraying. Non-destructive high-resolution neutron diffraction experiments were performed using the SALSA instrument at the Institut Laue-Langevin (ILL) to evaluate the local residual stress state in the as-sprayed condition. 2D maps of the residual stress distribution over the cross- sectional area of the samples were determined. Additionally, complementary laboratory X-ray diffraction (XRD) and incremental drilling analyses were carried out. The results indicate compressive residual stresses within the filled process zone, which are considered positive for the fatigue and wear resistance of the repaired components. Furthermore, metallographic examinations show a good bonding between the repair filling and the substrate as well as strongly deformed particles within the repaired region. The latter indicates significant plastic deformation during cold spraying, which is in agreement with the broader diffraction lines from the neutron and X-ray diffraction analyses in the filler compared to the substrate.
11:25 AM Conference Luncheon
12:25 PM Introductory Comments
12:30 PM
Design of Graded Transition Interlayer for Joining Inconel 740H Superalloy with P91 Steel using Wire-arc Additive Manufacturing: Soumya Sridar1; Xin Wang1; Mitra Shabani1; Michael Klecka2; Wei Xiong1; 1University of Pittsburgh; 2Raytheon Technologies Research Center
Design of an efficient interlayer is imperative for joining dissimilar materials using additive manufacturing to achieve smooth variation in properties. In this work, two graded transition interlayers were designed using a CALPHAD-based ICME framework (CALPHAD: Calculation of Phase Diagrams; ICME: Integrated Computational Materials Engineering) for joining Inconel 740H superalloy with P91 steel. Successful builds with the designed interlayers (60 and 85 wt.% P91) sandwiched between the constituent materials were fabricated using wire-arc additive manufacturing. The 60 wt.% P91 interlayer was found to exhibit an FCC matrix while the 85 wt.% P91 interlayer had a martensitic matrix. A two-step post-heat treatment consisting of homogenization and aging was designed. The key temperatures for each step were determined supported by CALPHAD-prediction of phase stability diagrams. The 60 wt.% P91 graded interlayer showed no improvement in hardness after aging. This agrees with the CALPHAD model predictions, which showed a lack of γ’ precipitates after aging for this composition. The hardness of 85 wt.% P91 improved considerably after aging with an optimum aging time of 8 hours. In addition, mechanical tests were performed to determine the location of failure as well as tensile properties. The 60% P91 graded interlayer builds failed at the interlayer while the 85% P91 build failed in the pure P91 region. This proves that the post-heat treated 85% P91 is much stronger than the pure P91 and hence, the strategy used in this work is successful for design of interlayers for dissimilar joining.
12:50 PM
Microstructure Evolution During Post-heat Treatment of Haynes 282 Alloy Processed by Wire-arc Additive Manufacturing: Luis Ladinos Pizano1; Soumya Sridar1; Chantal Sudbrack2; Wei Xiong1; 1University of Pittsburgh; 2National Energy Technology Laboratory
In order to perform microstructure engineering for improved mechanical properties, post-heat treatment optimization is imperative for additive manufacturing of advanced superalloys. In this work, the effect of solution heat treatment on the microstructural heterogeneity and γ’ precipitation for Haynes 282 fabricated using wire-arc additive manufacturing (WAAM) has been investigated. The results suggest that the standard solution heat treatment carried out at 1150°C for 2 hours is insufficient to remove the heterogeneities in the grain structure formed during WAAM. However, solution heat treatment at 1250°C for 2 hours promoted the dissolution of secondary precipitates and recrystallized the grain structure without causing excessive coarsening. In addition, solution heat treatment temperature affects the growth kinetics of γ’ precipitates. By increasing the solution treatment temperature, γ’ grows faster, achieving the peak hardness in a shorter aging time. Moreover, increasing the solution treatment temperature favors the development of a bimodal distribution of γ’ precipitates during aging. Tensile tests are performed for samples extracted from build (XZ) and transverse (YZ) planes to evaluate the effectiveness of the solution treatment in removing the microstructural heterogeneity. This work demonstrates the need for an effective post-heat treatment to eliminate the heterogeneities that form during the WAAM process and alter the γ’ precipitation and improve the mechanical properties of Haynes 282.
1:10 PM
Characterization of the Anisotropic Behaviour of Inconel 718 Parts Manufactured by Wire Arc Additve Manufacturing: Karin Hartl1; Christopher Wallis2; Martin Bielik2; Pier Curti2; Martin Stockinger1; 1Montanuniversität Leoben; 2RHP Technology GmbH
The usage of additive manufacturing as a process for component production is becoming increasingly important, as it offers enormous potential for material savings and therefore cost reduction. In particular, wire arc Directed Energy Deposition (wire arc DED) processes are arousing a great deal of interest in several industries by its high deposition rates at low equipment acquisition costs and the low buy-to-fly ratio. This process is being specifically investigated for aerospace and space applications, as it allows the production of large structural complex near-net-shape components in small batches. However, a major drawback of this technology is the high anisotropic behaviour of the manufactured structures in the as-welded state. Since the nickel-base alloy Inconel 718 is an anisotropic material, in which introduced textures strongly influence the mechanical properties, the impact of the wire arc DED processing route on the mechanical properties as well as the underlying microstructure is specifically focused on in this study. Using a plasma arc as heat source and Inconel 718 wire as feedstock material, test walls are produced in order to characterize the created material. In addition to the identification of factors influencing the process, temperature cycles are measured at different positions during the build-up. The resulting microstructure is subsequently evaluated macroscopically as well as microscopically and examined regarding pores and precipitates. SEM/EDX analysis is carried out to investigate the underlying microstructure of the additively manufactured parts. Furthermore, mechanical properties are evaluated in the build-up direction as well as transversal to this direction in order to characterize the anisotropy of the material.
1:30 PM
Keyhole TIG Welding of New Co-lean Nickel-based Superalloy G27: Achmad Ariaseta1; Dario Pick1; Joel Andersson1; Olanrewaju Ojo2; 1University West; 2University of Manitoba
The hot sections of aircraft engines have been preferably fabricated by joining small pieces of superalloys by the welding process instead of casting a single large component due to several benefits, such as reducing the total weight of the components and enhancing the design flexibility. The welding process and the associated control themselves, to some extent, have enhanced remarkably in the last decades. One of the recent welding techniques is Keyhole TIG (K-TIG) welding which has the capability to use lower heat input and higher energy density to achieve deeper penetration during the welding compared to the traditional one, being essential when joining superalloys in the hot sections of an aircraft engine in the aerospace industry. Alloy G27, a new Co-lean nickel-based superalloy with service temperature capability up to about 760 °C, is a promising material candidate to be utilized in the fabrication of aero-engine hot sections. From the industrial perspective, it is of paramount importance to produce a superalloy weld that meets the tight quality criteria in aerospace applications in terms of weld geometry and weld defects. Moreover, understanding the microstructures in the heat-affected zone (HAZ) and fusion zone (FZ) is essential since they influence the properties and integrity of the weldment and will become the basis for developing suitable post-weld heat treatment. Thus, this article aims to study the effect of K-TIG welding parameters on weld geometry and weld defects of G27 and to characterize the microstructures in HAZ and FZ of the welded alloy.
1:50 PM Concluding Comments