CoCrFeMnNi high-entropy alloy is a new engineering material with great potential for application in micro- and nano- electromechanical systems due to its excellent mechanical properties. The devices that are made from CoCrFeMnNi high-entropy alloy are inevitably subjected to a kind of scratch loading in service. The surface of high-entropy alloy contains micro- and nano-scale surface roughness with different surface morphologies in practical applications. Molecular dynamics simulations are adopted to investigate the scratch deformation behavior and crystal structure evolution of single crystal CoCrFeMnNi high-entropy alloy to improve the assembly accuracy and service reliability of nano-high entropy alloy devices. The effects of planar, rectangular and triangular surface textures and scratch tip radius on the scratch response of CoCrFeMnNi high-entropy alloy are discussed.
The molecular dynamics model consists of a high-entropy alloy specimen and a diamond scratch tip, where the high-entropy alloy specimen is divided into a Newtonian layer, a thermostat layer and a fixed layer. In the scratch process, the scratch tip is scraped from the initial position along the negative X-direction at a speed of 100 m/s and an initial temperature of 300 K. The scratch depth is set to 1.2 nm. The second nearest-neighbor modified-embedded-atom-method potential for CoCrFeMnNi high-entropy alloy is used to describe the interaction between the CoCrFeMnNi high-entropy alloy.
The results show that the average tangential and normal forces of the planar surface textures are significantly higher than those of the nonplanar-type textures during the scratch of CoCrFeMnNi high-entropy alloy. For CoCrFeMnNi high-entropy alloy with planar, rectangular and triangular surface textures, the plane-type morphology samples show the maximum friction coefficient. For the non-planar type textures, the base grooves behind the scratch tip are completely destroyed after the scratch, and the lattices of the corresponding base grooves show severe distortion; for the planar type textures, the surface in front of the scratch tip is convex and uneven; the atom buildup is observed in front of the scratch tip for the rectangular and triangular type textures.
For different scratch tip radii, the height of atomic buildup in the planar surface textures is significantly higher than that in the rectangular and triangular type surface textures. For the planar, rectangular and triangular surface textures, the atomic accumulation height in front of the scratch tip increases with the increase of scratch tip radius. At the scratch depth of 1.2 nm, the nonplanar-type textures reduce the plastic deformation and friction coefficient in the scratch region by dislocation annihilation, which leads to a friction reduction effect. The results further show that the main plastic deformation mechanism of single crystal CoCrFeMnNi high-entropy alloy during scratch deformation is the slipping deformation of Shockley partial dislocation.
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