In Situ Study of the Stress Relaxation During Aging of Nickel-Base Superalloy Forgings
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EREA is with the Institut Max Von Laue - Paul Langevin, 71 Avenue des Martyrs 38000 Grenoble, France and also with the School of Materials, University of Manchester, Manchester, M13 9PL, UK. Contact e-mail: [email protected] P.J. WITHERS and M. PREUSS are with the School of Materials, University of Manchester. T. PIRLING is with the Institut Max Von Laue - Paul Langevin. A. PARADOWSKA is with the OPAL, Ansto, Kirrawee DC, NSW 2232, Australia. D. MA is with the Neutron Scattering Division, Spallation Neutron Source, Oak Ridge National Laboratory, TN 37831-6139. Manuscript submitted November 28, 2018. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/dow nloads/doe-public-access-plan). Article published online June 3, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
INTRODUCTION
NI-BASE superalloys are widely used for aeroengine applications and in the energy sector due to their exceptional mechanical strength and creep resistance at high temperature.[1] Depending on the microstructure, temperature capability, and mechanical property requirements, different superalloys are used for the manufacturing of disks and blades for the hot section of aeroengines. Inconel 718 and Udimet 720LI are among the most widely used Ni-base superalloys. Inconel 718 is strengthened by having a combination of c¢¢ and c¢ precipitates amounting to about 25vol pct,[2] while Udimet 720LI is strengthened by approximately 45 vol pct of c¢.[3] The high-volume fractions of these precipitates allows these alloys to operate under extreme mechanical conditions at temperatures exceeding 600 C in the case of Udimet 720LI.[1] The manufacturing process of polycrystalline Ni-base superalloy components typically involves several thermomechanical steps, many of which result in the generation of significant residual stresses. In particular, processes such as forging followed by quenching/fast cooling generate very high level of residual stress in Ni-base superalloys.[4–7] Consequently, there is a requirement to precisely control and minimize the residual stress distribution because they can lead to distortion during machining and they VOLUME 50A, AUGUST 2019—3555
superimpose on the operating stresses which can significantly reduce component life in-service.[8] Residual stresses are mitigated by means of thermal stress relaxation through the application of an annealing treatment, which also serves the purpose of an aging treatment precipitating or optimizing the distribution of t
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