Plasticity induced by nanoindentation in a CrCoNi medium-entropy alloy studied by accurate electron channeling contrast imaging revealing dislocation-low angle grain boundary interactions

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:817

Article

Habiyaremye, Frederic¹  Guitton, Antoine^1,2  Schafer, Florian³  Scholz, Felicitas⁴  Schneider, Mike⁴  Frenzel, Jan⁴  Laplanche, Guillaume⁴  Maloufi, Nabila^1,2 

[1] Univ Lorraine, CNRS, Arts & Metiers, LEM3, F-57070 Metz, France

[2] Univ Lorraine, Labex Damas, F-57073 Metz, France

[3] Saarland Univ, Dept Mat Sci & Engn, D-66123 Saarbrucken, Germany

[4] Ruhr Univ Bochum, Inst Werkstoffe, Univ Str 150, D-44801 Bochum, Germany

关键词: Dislocations;    Low-angle grain boundary;    NiCoCr medium-entropy alloy;    A-ECCI;    Nanoindentation;   

DOI  :  10.1016/j.msea.2021.141364

来源: Elsevier

【 摘 要 】

In the present work, interactions of nanoindentation-induced dislocations (NIDs) with a low-angle grain boundary (LAGB) are investigated in a single-crystalline CrCoNi medium-entropy alloy (MEA). Microstructural evolutions before and after nanoindentation were examined using accurate electron channeling contrast imaging (A-ECCI). In the as-grown state, the alloy microstructure consists of subgrains separated by LAGBs. After nanoindentation on the (001) plane far away from LAGBs, the load-displacement curves exhibit the typical behavior of metals and alloys with a pop-in marking the elastic-plastic transition. This pop-in is related to the nucleation of NIDs that are observed to form pile-ups on {111} planes. In contrast, when indents are performed in the vicinity of a LAGB with a low misorientation angle of 0.24 degrees and consisting of dislocations spaced similar to 60 nm apart, different micromechanical responses and deformation mechanisms are observed depending on the distance between the LAGB and the nanoindenter tip. When the distance between the LAGB and the nanoindenter tip is larger than four times the size of the indent (corresponding ratio: R > 4), the LAGB does not affect the micromechanical response nor interact with NIDs. In contrast, when the indenter comes in direct or indirect contact with the LAGB (R < 1), the load-displacement curve deviates at low loads from the elastic stage, and popins are not observed. In this case, the continuous deformation is accommodated by the movement of the preexisting LAGB dislocations. For intermediate cases with 1 < R < 4, the load of the initial pop-in is dependent on the local defect density. In this latter case, the pile-ups of NIDs directly impinge on the LAGB. Microstructural analyses reveal that the LAGB accommodates plasticity by blocking the NIDs, activating a dislocation nucleation site in the adjacent subgrain/emission of dislocation from the LAGB, and inducing slight motions of its constituent dislocations.

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