Unusual strain hardening response and ductility of NiCoCr equiatomic alloy were investigated through microstructural analysis of [111], [110] and [123] single crystals deformed under tension. Nano-twinning prevailed at, as early as, 4% strain along the [110] orientation, providing a steady work hardening, and thereby a significant ductility. While single slip dominated in the [123] orientation at the early stages of deformation, multiple slip and nanotwinning was prominent in the [111] orientation. Significant dislocation storage capability and resistance to necking due to nanotwinning provided unprecedented ductility to NiCoCr medium entropy alloys, making it superior than quinary variants, and conventional low and medium stacking fault energy steels. IMPACT STATEMENT A comparison of the current results on the ternary medium entropy alloy single crystals and those previously reported on the quinary and quaternary fcc equiatomic alloys demonstrates that a higher configurational entropy does not necessarily warrant improved mechanical properties.
Nickel-Titanium (NiTi) shape memory alloys continue to attract significant attention in medicine due to their superior shape memory and pseudoelastic properties, especially in the fields of cardiovascular surgery and orthodontics [1][2][3][4]. The pseudoelastic behavior stands out in dental applications: for instance, in the case of orthodontic archwires, the pseudoelastic property of NiTi makes the application of constant stress possible over large tooth displacements [1,2], which not only minimizes tissue damage during treatment [5], but also eliminates readjustment procedures -which are quite uncomfortable for the patients -required for archwires made of conventional materials, such as medical grade stainless steel [1,[6][7][8][9]. Specifically,
Micro/nanoscale textured surfaces have presented promising tissue-implant integration via increasing surface roughness, energy, and wettability. Recent studies indicate that surface texture imparted on the metallic implants via surface relief induced with simple bulk plastic deformation methods (e.g., tension or compression tests) does result in enhanced cell response. Considering these recent findings, this study presents a thorough investigation of the effects of surface relief on surface properties of implants and cell adhesion. Experiments are conducted on the samples subjected to interrupted tensile tests up to the plastic strains of 5, 15, 25, and 35%. Main findings from these experiments suggest that, as the plastic deformation level increases up to 35% from the undeformed (control) level, (1) average surface roughness (R a ) increases from 17.58 to 595.29 nm; (2) water contact angle decreases from 84.28 to 58.07 • ; (3) surface free energy (SFE) increases from 36.06 to 48.89 mJ/m 2 ; and (4) breast cancer cells show 2.4-fold increased number of attachment. Increased surface roughness indicates the distorted topography via surface relief and leads to increased wettability, consistent with Wenzel's theory. The higher levels of SFE observed were related to high-energy regions provided via activation of strengthening mechanisms, which increased in volume fraction concomitant with plastic deformation. Eventually, the displayed improvements in surface properties have increased the number of breast cancer cell attachments. These findings indicate that surface relief induced upon plastic deformation processes could be utilized in the design of implants for therapeutic or diagnostic purposes through capturing breast cancer cells on the material surface.
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