Experimental study of elementary deformation mechanisms around a low-angle grain boundary in a single crystalline CrCoNi medium-entropy alloy.

The interactions of dislocations with point, planar and volumetric defects have been studied by experimental, theoretical and computational approaches over the last couple of decades. These studies have been central to the current understanding of the general mechanisms of plastic deformation in polycrystalline materials [1-2]. The dislocation-grain boundary (GB) interactions significantly influence the yield strength of materials as proven by the Hall-Petch relationship [3-4]. However, this relationship does not provide the contribution of an individual and isolated GB to the overall strength. Few studies have experimentally cope with this issue by isolating a specific boundary, introducing local deformation near it, and observing changes of the deformation microstructure [5] and/or mechanical properties [6]. Although such studies suggest that distinct GBs differently accommodate plastic deformation, they have not been able to determine to what extent and how dislocations interact with different and individual GBs on different length scales. Based on those prior studies, dislocation-low angle GB (LAGB) interactions were studied in a single crystal of the equiatomic CrCoNi medium-entropy alloy. Local plastic deformation at varying distances from the boundary was carried out using an nanoindenter with a Berkovich indenter tip coupled with an atomic force microscope (AFM). Microstructural characterization around the LAGB was performed prior to and after plastic deformation using accurate electron channeling contrast imaging [7,8] and electron backscatter diffraction (EBSD). Dislocations and other defects were observed and analyzed around the LAGB and its responses to the localized plastic deformation were reported in detail [9]. References [1] – A. Cottrell, Dislocations and plastic flow in crystals, Clarendon Press, Oxford, (1963). [2] – L. Priester. Grain boundary and crystalline plasticity. ISTE Ltd, London, (2011). [3] – N. Hansen. Scripta Materialia 51, (2004). [4] – M. Schneider, E.P. George, T.J. Manescau, T Zaležak, J. Hunfeld, A. Dlouhy, G. Eggeler, G. Laplanche. International Journal of Plasticity 124, (2020). [5] – A. Guitton, H. Kriaa, E. Bouzy, J. Guyon and N. Maloufi. Materials 11, ( 2018). [6] – J.S. Vachhani, R.D. Doherty, and S.R. Kalidindi. International Journal of Plasticity 81, (2016). [7] – H. Mansour, J. Guyon, M.A. Crimp, N. Gey, B. Beausir, N. Maloufi. Scripta Materialia 84-85, (2014). [8] – Kriaa, H.; Guitton, A. and Maloufi, N. Scientific report 7, (2017). [9] – F. Habiyaremye, N. Maloufi, F. Schafer, G. Laplanche, A. Guitton. To be submitted (2020)