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    Mechanical behavior of medium and high entropy alloys
    (Karabük Üniversitesi, Lisansüstü Eğitim Enstitüsü, 2024) Madkhanah, Ahmad; Pıçak, Sezer
    Medium- and high-entropy alloys (M/HEAs) provide a vast and diverse design space compared to traditional alloys, creating new opportunities for uncovering un-explored physics and functionalities. Some of these alloys demonstrate an excep-tional combination of high strength and ductility, which has been attributed to the activation of multiple deformation mechanisms initiated by low- and medium-energy stacking faults. Despite numerous recent studies investigating the micro-scopic and macroscopic properties of these materials, research on single crystalline M/HEAs is notably lacking. Such studies are crucial for gaining a deeper under-standing of the fundamental deformation mechanisms. In response to this gap, the current study focuses on fabricating and characterizing single and polycrystalline M/HEAs to explore the underlying deformation processes responsible for their re-markable mechanical behavior. In this work, the tensile deformation behavior of NiCoCr single crystals was studied along different crystallographic orientations, including [001], [011] and [111]. De-tailed microstructural analyses were carried out to identify the dominant mecha-nisms during deformation and compared with the existing literature. Through ex-tensive characterization of bulk single crystals, it was found that the exceptional mechanical properties of NiCoCr result from short-range atomic order (SRO). This SRO promotes the simultaneous activation of twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP), which leads to dynamic hardening by restricting dislocation motion through the formation of nanoscale twin and marten-site boundaries. These findings suggest that the interaction between SRO and plas-ticity can be harnessed to activate various deformation mechanisms, potentially leading to the discovery of new M/HEAs with unprecedented mechanical proper-ties.