SKM 2023 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 40: Mechanical Properties and Allloy Design

MM 40.6: Talk

Thursday, March 30, 2023, 17:15–17:30, SCH A 251

Can we measure twinning stress of a high entropy alloy with micromechanics? — •Camila Aguiar Teixeira, Subin Lee, and Christoph Kirchlechner — Institute for Applied Materials, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany

CoCrFeMnNi and CoCrNi high entropy alloys (HEAs) have attracted attention due to their mechanical properties. Extensive mechanical twinning is mainly responsible for their outstanding mechanical response under cryogenic temperatures, e.g. increase in ductility and tensile strength. However, at room temperature dislocation slip is dominant and twinning only observed in highly deformed samples. Although both HEAs have been broadly studied, there is still a lack of in-depth understanding of twinning mechanism and stresses required for its activation, which is crucial for advanced HEAs design. In this work, we aim to develop protocols to assess the critical resolved shear stress required for twinning by applying in situ micromechanics. Therefore, two points were addressed within the scope of this work: (i) study the transition from full to partial slip using micropillar compression and (ii) observe deformation twinning by shear stress using micro-shear test. Specific grain orientations were chosen through EBSD analyses, for the micropillar single slip orientation with higher Schmid factor for partial slip and for micro-shear [1 1 2] ND and [-1 1 1] TD orientation. Samples were then micromachined by FIB and tested in situ. Post-mortem analysis included SEM imaging, EBSD and (S)TEM to verify if twinning could be observed. The results provided quantitative insights essential for further understanding of the twinning mechanisms.