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Dislocation-scale characterization of the evolution of deformation microstructures on bulk materials. Case of TiAl alloys

Abstract : Developing new materials and understanding how they deform is the main challenge of engineers in order to follow and predict the fast evolutions of our society. For instance, in a framework of energetic cost reductions, titanium aluminide (TiAl) alloys have attracted considerable attention due to their unique combination of properties such as high specific strength and stiffness, good creep properties and resistance against oxidation and corrosion, which make them suitable candidate materials for high temperature applications [1]. However, TiAl alloys are brittle at Room Temperature (RT), i.e. below their brittle-to-ductile transition temperature, which lies between 800°C and 1000°C [2]. Furthermore, their complex microstructures (multiphase, different types of microstructures, specific dislocation mechanisms…) with several impacts at different scales are puzzling the materials science community. Despite intense research, literature suffers from a lack of understanding of their elementary deformation mechanisms and the precise role of microstructures [2]. In order to address these questions, we report here, an original and an innovative approach bringing the necessary information, thus allowing linking the multiscale aspects of the mechanical behavior of TiAl alloys at RT. Particularly, we bring new breakthrough on the evolution of deformation microstructures at RT in the vicinity of interfaces in γ phase of a dual-phase bulk TiAl alloy. Plastic deformation is induced locally by µN-nanoindentation. The evolution of the microstructures is characterized comprehensively by accurate Electron Channeling Contrast Imaging (aECCI) before and after deformation [3]. aECCI is a non-destructive groundbreaking procedure offering the ability to provide, inside a SEM, TEM-like diffraction contrast imaging of sub-surface defects (at a depth of about one hundred of nanometers) on centimetric bulk specimen with still unsurpassed resolutions [4]. Defects, such as dislocations, can be characterized by applying the TEM extinction criteria [5]. All features help to explain the poor ductility of the TiAl-based alloys at RT. Accommodation of the deformation is reported and a scenario is proposed [3]. References [1] – Y. Kim, D. Dimiduk, JOM 43, (1991). [2] – C. Zambaldi, Thèse, Aachen (2010). [3] – A. Guitton, H. Kriaa, E. Bouzy, J. Guyon, N. Maloufi, Materials 11, 2 (2018) [4] – H. Kriaa, A. Guitton, N. Maloufi, Scientific reports 7, (2017). [5] – H. Kriaa, A. Guitton, N. Maloufi, Materials 11 (2018)
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Submitted on : Monday, December 7, 2020 - 10:23:16 AM
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  • HAL Id : hal-03043122, version 1


Antoine Guitton, Hana Kriaa, Emmanuel Bouzy, Julien Guyon, Nabila Maloufi. Dislocation-scale characterization of the evolution of deformation microstructures on bulk materials. Case of TiAl alloys. Matériaux, 2018, Strasbourg, France. ⟨hal-03043122⟩



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