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Shape prediction of a hot formed component in nickel-base superalloys
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. RISE IVF AB. (Solid Mechanics)ORCID iD: 0000-0002-1432-444X
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. RISE IVF AB. (Solid Mechanics)
GKN Aerospace Sweden AB.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials. (Solid Mechanics)ORCID iD: 0000-0001-7074-8960
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Current manufacturing processes of advanced aero engine components in nickel-base superalloys are performed at approximately 950 °C, with varying holding times, to reduce the amount of residual stresses, and thereby shape deviations, over the part. The aim of such procedures is to obtain the final geometry of the component within tolerance and avoid costly tryouts, which can be unfavorable to the competitiveness of the aerospace industry. In addition, a reduction in the forming temperature or holding time may significantly reduce the energy consumption and carbon dioxide (CO2) emissions while increasing the ecological sustainability of the process. In this work, the numerical study of a hot forming procedure of a double-curved component in Haynes® 282® is presented. The influence of the forming temperature and holding time on the predicted amount of springback at different stages of the hot forming procedure is assessed. The resulting shape distortions are compared with identical FE analyses in alloy 718 at 870 °C available in literature. The anisotropic properties of the material are determined at temperatures ranging from 20 to 1000 °C. A qualitative analysis of the different types of serrations present in the hardening curves between 300 and 900 °C is included in the study. Microstructural observations of selected specimens are correlated to the material-characterization tests. The thermo-mechanical data is used as input to the novel version of the Barlat Yld2000-2D material model in LS-DYNA. The results show that forming of Haynes® 282® at 870 °C produces high shape distortions over the part with values beyond the sheet thickness, in contrast to the response of alloy 718. A comparison of the stress-relaxation rate with available data in literature for alloy 718 at 870 °C reveals that Haynes® 282® relaxes about 50% slower than alloy 718, whereas reasonably analogous at 950 °C. An increase in the forming temperature to 950 °C significantly reduces the amount of springback. Therefore, it can be concluded that forming of Haynes® 282® requires a higher temperature than reported for alloy 718 to reach similar amount of springback. The presented studies indicate that the use of advanced anisotropic models together with the thermo-mechanical properties and stress-relaxation behavior of the material is of utmost importance to accurately predict the final geometry of lightweight components of interest to the aerospace industry.

Keywords [en]
anisotropy, hot forming, alloy 718, Haynes 282, stress relaxation, superalloy
National Category
Metallurgy and Metallic Materials Manufacturing, Surface and Joining Technology
Research subject
Solid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-76239OAI: oai:DiVA.org:ltu-76239DiVA, id: diva2:1357614
Projects
Validation of a fabrication procedure for bi-metallic aero engine components in superalloys (NFFP7)
Funder
Vinnova, 2017-04849Available from: 2019-10-04 Created: 2019-10-04 Last updated: 2019-10-04
In thesis
1. Modelling Aspects in Forming and Welding of Nickel-Base Superalloys
Open this publication in new window or tab >>Modelling Aspects in Forming and Welding of Nickel-Base Superalloys
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The reduction of fuel consumption and carbon dioxide emissions are currently a key factor for the aviation industry because of major concerns about climate change and more restrictive environmental laws. One way to reduce both fuel consumption and CO2 emissions is by significantly decreasing the weight of vehicles while increasing the efficiency of the engine. To meet these requirements, the European aero-engine industry is continuously focusing on improved engine designs and alternative manufacturing methods for load-carrying structures in advanced materials, such as titanium and nickel-base superalloys. These new manufacturing methods involve sheet-metal parts, small castings, and forgings assembled using welding, enabling flexible designs where each part is made of the most suitable materials and states, with advantages such as reduced product cost, lower weight, and increased engine efficiency.

In this thesis, a manufacturing process chain including forming and welding in two nickel-base superalloys, alloy 718 and Haynes® 282®, is studied. The aim of this work is to determine which aspects within the material and process are the most relevant to accurately predict the amount of shape distortions that occur along the manufacturing chain. The effect of the forming temperature on the predicted springback is included. The results are compared with experimental cold and hot forming tests with a subsequent welding procedure. During forming of a double-curved component in alloy 718 at room temperature, open fractures are observed in the drawbead regions, which could not be predicted while evaluating the formability of the material based on Nakazima tests and forming limit curves (FLC). The generalised incremental stress-state dependent damage model (GISSMO) is calibrated and coupled with the anisotropic Barlat Yld2000-2D material model to accurately predict material failure during forming using LS-DYNA. The mechanical properties of alloy 718 are determined via uniaxial tensile, plane strain, shear, and biaxial tests at 20 °C. The deformations are continuously evaluated using the digital image correlation (DIC) system ARAMIS™. Numerical predictions are able to accurately predict failure on the same regions as observed during the experimental forming tests. Comparisons of the distribution of damage on one of the drawbeads, between simulations and damage measurements by acoustic emission, indicate that higher damage values correspond to bigger micro cracks. The history from the sheet-metal forming procedure, i.e. residual stresses, strains, element thickness, and geometry, is used as the input for the FE analysis of a subsequent welding procedure of a strip geometry in alloy 718 and Haynes® 282®. A comprehensive characterization of the elasto-plastic properties of both alloys between 20 and 1000 °C is included. Other temperature-dependent properties are extracted from JMatPro-v9 for the corresponding specific batches. The results from the simulations show that the welding procedure further increases the shape distortions over the part. Encouraging agreement was found between the model predictions and the results of forming and welding tests in alloy 718. The findings underscore the importance of including the material history and accurate process conditions along the manufacturing chain to both the prediction accuracy of accumulated shape distortions, and to the potential for the industry.

The work also comprises hot forming of the double-curved component in alloy 718 and Haynes® 282®. The presence and nature of serrations due to the dynamic strain aging (DSA) phenomenon between 300 and 800 °C is studied. Microstructural observations are consistent with the behaviour of the material at the different temperatures tested. The residual stresses obtained from the hot forming simulations are transformed based on the stress-relaxation tests performed at high temperatures ranging from 700 to 1000 °C. The results show the importance of using the novel modelling approach combining the anisotropic Barlat Yld2000-2D material model with the thermo-mechanical properties and stress-relaxation behaviour of the material to predict the final geometry of the component with high accuracy. A welding simulation of a bi-metallic strip geometry obtained from the hot formed double-curved component is performed numerically. The effect of the two superalloys on the shape distortions over the part is discussed.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2019
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Keywords
alloy 718, Haynes 282, cold forming, hot forming, material characterization, GISSMO, welding, heat treatment, manufacturing chain, springback, shape distortions, dynamic strain aging, DSA, microstructure
National Category
Metallurgy and Metallic Materials Manufacturing, Surface and Joining Technology
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:ltu:diva-76243 (URN)978-91-7790-460-1 (ISBN)978-91-7790-461-8 (ISBN)
Public defence
2019-11-29, E231, Luleå, 09:00 (English)
Opponent
Supervisors
Projects
Virtual process chain for superalloy sheet metal aero engine structures - Validation and demonstrator (NFFP6)Validation of a fabrication procedure for bi-metallic aero engine components in superalloys (NFFP7)
Funder
Vinnova, 2013-01173 and 2017-04849
Available from: 2019-10-04 Created: 2019-10-04 Last updated: 2019-11-14Bibliographically approved

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