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The ultrafine-grained (UFG) structure (∼100 nm) of CoCrFeMnNi high-entropy alloy was achieved using cryogenic multi-pass caliber rolling at 77 K to impose less deformation (e = 1) compared to severe plastic deformation (SPD, e > 4). Highly increased twinning activity at 77 K caused the grain interiors to fragment significantly, so UFG structure could be induced without imposing SPD. Intersected twin morphology and secondary twins played a key role in twinning-induced grain refinement to achieve UFG structure. The processed material showed an exceptional high yield strength of ∼1.5 GPa with a reasonable fracture elongation of ∼10% at room temperature.

The present study numerically investigated the characteristics of flow and heat transfer in a channel with a newly designed surface called a tear-drop dimple on the bottom wall by deforming the upstream shape of a dimple cavity. Direct numerical simulations (DNS) were carried out with a Reynolds number of 2800 based on the mean velocity and channel height. A Prandtl number of 0.71 was considered. The present study considered six different cases, consisting of one general dimple case and five tear-drop dimple cases where only the length of the upstream cavity was changed. The overall performance was assessed using volume goodness factors. The notable flow characteristics observed in this study include the circulation, which is classified into two types: spanwise circulation and streamwise swirling motion. The pressure loss and heat transfer are influenced by the two types of flow patterns. A comparison of the thermo-hydraulic performances of the tear-drop dimples and those of the general dimple confirms the advantage of the tear-drop dimple shape over the general dimple.