The AD730 superalloy was developed by Aubert et Duval in sight of replacing Inconel718 which is currently the principal material used in the fabrication of turbine disks. A successful change of material in this domain could lead to an increase of temperature in the combustion chamber and therefore an increase of the efficiency of the turbojet engine. The AD730 superalloy is relatively recent and its fabrication process (hot forging) has never been studied in an academic environment.
The purpose of this work is to increase the knowledge of the hardening mechanism which takes place during hot forging, found to be principally a mechanism of recrystallization. Hot compression tests were accomplished with a series of increased deformations (0,08; 0,12; 0,24; 0,40; 0,63) and different stain rates (0,1; 0,01; 0,001 s-1) in order to study the evolution of recrystallization. A deformation temperature of 1120°C and a holding time of 5 minutes were chosen as optimal compression parameters. The tests were completed on a servohydraulic MTS press. Special attention was given in understanding the impact of lubrication on the stress/strain curve. More tests were done at different temperatures (1060; 1090; 1120; 1150 °C) and different strain rates (0,001; 0,01; 0,1; 1 s-1) with the aim to develop a model which can predict the material behaviour.
The Yield Drop phenomenon was observed and analysed. Theoretical research and experimental validation were used to support a potential explanation of the phenomenon. The double differentiation method revealed two critical strains at [deformation] =0,08 and [deformation] =0,12, which could be associated with the initiation of a mechanism involved specifically in hot forging, such as dynamic recrystallization. Microstructural observation showed an increasing number of small grains between a strain level of strain 0,08 and 0,12. This confirms that dynamic recrystallization starts at for a strain of 0,08. The Arrhenius type model, which was built to predict material behaviour, has an error of 7% with our experimental data. This error confirmed the model to be appropriate for our material even if results at high strain rates are close to experimental data resulting from a low strain rate ([vitesse de déformation] = 0,001 s -1).
| Date | 30 Aug 2016 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Mohammad Jahazi (Supervisor) |
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Lieutaud, M. (Author),
Jahazi (Supervisor),
30 Aug 2016Student thesis: Master's thesis › Master in Engineering: Mechanical Engineering