Superalloys 2021: Tuesday Part I - Disk Alloy Manufacture
Program Organizers: Sammy Tin, University of Arizona; Christopher O'Brien, ATI Specialty Materials; Justin Clews, Pratt & Whitney; Jonathan Cormier, ENSMA - Institut Pprime - UPR CNRS 3346; Qiang Feng, University of Science and Technology Beijing; Mark Hardy, Rolls-Royce Plc; John Marcin, Collins Aerospace; Akane Suzuki, GE Aerospace Research
Tuesday 8:30 AM
September 14, 2021
Room: Live Session Room
Location: Virtual Event
Session Chair: Christopher O'Brien, ATI Specialty Materials; Zhongnan Bi, Central Iron and Steel Research Institute
8:30 AM
Gamma Prime Precipitate Evolution during Hot Forging of a γ- γ’ Ni-based Superalloy at Subsolvus Temperatures: Marcos Perez1; Christian Dumont2; Sebastien Nouveau2; 1AFRC; 2Aubert & Duval
Nickel superalloys are used to manufacture high temperature rotating engine parts such as high pressure disks in gas turbine engines. Alloy 720Li (720Li) is a precipitation-hardened Ni-based superalloy commonly produced by cast and wrought processes. Conventional ingot-to-billet conversion is an expensive and very complex process, requiring multiple open die forging operations and reheating steps in order to achieve a homogeneous microstructure. The present work studies the microstructural evolution of 720Li billet material with the presence of large unrecrystallized structures. The interaction of ’ precipitates with recrystallization during hot forging at subsolvus temperatures was investigated. Double truncated cones were forged at subsolvus temperatures following two forging approaches: single blow and double blow with an intermediate heat treatment. Combined EBSD-EDX analysis was employed to characterize the microstructural evolution of 720Li during hot forging operations. Primary ’ precipitates promote heteroepitaxial recrystallization during slow cooling, whereas secondary precipitates, formed during slow cooling are not dissolved during reheating, prior to the forging operations. The presence of undissolved secondary ’ promotes strain accumulation and the occurrence of continuous dynamic recrystallization (CDRX). Intermediate heat treatment plays an instrumental role on the recrystallization behaviour for the alloy 720Li. Dissolution of the secondary ’ precipitates results in a strong preconditioning of the 720Li microstructure prior to the second blow of deformation, promoting the formation of fully recrystallized structures and removing the undesired large unrecrystallized regions. The coalescence of intragranular ’ precipitates into clusters of coalesced ’ precipitates represents a clear transition from the apparent unrecrystallized regions to the fully recrystallized structures.
8:55 AM
Dynamic and Post-dynamic Recrystallization during Supersolvus Forging of the New Nickel-based Superalloy – VDM Alloy 780: Juhi Sharma1; Masood Hafez2; Bodo Gehrmann2; Charbel Moussa1; Nathalie Bozzolo1; 1MINES ParisTech - CEMEF; 2VDM Metals International GmbH
The need of developing new high temperature materials has increased significantly in the last decades owing to the demand of higher aerospace engine operating temperatures. This requires improved microstructural stability of the polycrystalline nickel-based superalloys used for turbine disks. The microstructure of VDM Alloy 780 consists of ??′ strengthening precipitates in addition to the needle/plate-shaped particles (of ä and/or ç phase) to pin the grain boundaries. The present article aims at discussing the recrystallization behavior of the new VDM Alloy 780 in the supersolvus domain. Both dynamic and post-dynamic microstructural evolutions are reported. The dynamic recrystallization (DRX) kinetics was found to be rather sluggish. For a plastic strain of 1.3 at 1050 °C applied at a strain rate of 0.01 s-1, the microstructure of VDM Alloy 780 is only 50 % recrystallized. The DRX grain sizes are quite close for the two applied strain rates - 0.01 s-1 and 0.1 s-1. Despite slow DRX kinetics, the fast post-dynamic evolutions allowed to achieve fully recrystallized microstructures with a grain size of 26 ìm within 5 minutes of post-deformation holding at 1050 °C. The post-dynamically recrystallized grain sizes were predominantly temperature dependent and were not sensitive to strains and strain rates within the applied range. Deformation followed by 5 minutes holding at temperatures below 1050 °C but still in the single phase domain could eventually generate finer grain sizes (< 20 ìm). The low sensitivity of the grain size obtained after post-dynamic evolution to the applied strain and strain rates is an advantage for the industrial forging routes wherein the deformation conditions can vary over the piece. Another advantage of this alloy is the relatively slow grain growth kinetics which makes possible to obtain homogenous and reasonably fine microstructures after supersolvus forging.
9:20 AM
Aspects of High Strain Rate Industrial Forging of Inconel 718: Aleksey Reshetov1; Nicola Stefani1; Olga Bylya1; Bhaskaran Krishnamurthy1; Paul Blackwell1; 1University of Strathclyde
The major part of all material and microstructural data used for the modelling of nickel superalloy forgings are obtained from uniaxial laboratory tests with limited plastic strain and very simple thermo-mechanical history. At the same time, new challenges in near-net shape industrial forging require a high level of reliability of modelling prediction of metal flow, for predicting the risk of defects and microstructural transformation. A few recently conducted benchmarking studies have shown that despite the availability of various material models (including microstructural ones) embedded in commercial FE software, in many cases, the level of prediction remains unsatisfactory. This is especially true for Fast Industrial Forging Processes (like screw press or hammer forgings). This paper suggests a methodology for processing the results from industrial forgings for obtaining robust data for calibration, validation and improvement of material and microstructural models. This also can provide additional information on the material science behind the microstructural phenomena, which are problematic to capture and study using simple uniaxial tests.
9:45 AM Question and Answer Period