Uniaxial pulling and nano-scratching of a newly synthesised high entropy

Fan, Pengfei and Katiyar, Nirmal Kumar and Zhou, Xiaowang and Goel, Saurav (2022) Uniaxial pulling and nano-scratching of a newly synthesised high entropy. APL Materials, 10 (11). 111118. ISSN 2166-532X (https://doi.org/10.1063/5.0128135)

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Abstract

Multi component alloys possessing nanocrystalline structure, often alluded to be as Cantor alloys or high entropy alloys (HEAs), continues to attract great attention of the research community. It has been suggested that about 64 elements in the periodic table can be mixed in various compositions to synthesize as many as ~108 different types of HEA alloys. Most HEA's possess a face centered cubic or a body centered cubic crystal structure. The nanomechanical studies on any types of HEA combining experimental and atomic simulations are rather scarce in literature, which was a major motivation behind this work. In this spirit, a novel high entropy alloy (Ni25Cu18.75Fe25Co25Al6.25) was synthesized using arc melting method which followed a joint simulation and experimental effort to investigate dislocation mediated plastic mechanisms in HEA. The investigation takes advantage of an Embedded atomic method (EAM) type potential energy function corroborating the material composition to perform the nanoscale tensile and scratch MD simulation studies followed by experimental nano-scratching to investigate plasticity and material removal mechanisms, aspects related to nanofriction and nanotribology, side flow, pileup and crystal defects formed in the sub-surface as an elasto-plastic material response of the HEA during and after the scratch process. The major types of crystal defects associated with the plastic deformation of the crystalline face centred cubic structure of HEA were 2,3,4-hcp layered like defect coordination structure, coherent ∑3 twin boundary and ∑11 fault or tilt boundary, in combination with Stair rods, Hirth locks, Frank partials and Lomer–Cottrell (LC) locks. They formed much of the damage in the sub-surface and side-flow mechanisms. Moreover, 1/6 Shockley with exceptionally larger dislocation loops were seen to be the transporters of stacking faults deeper into the substrate than the location of the applied cutting load. The (100) orientation showed the highest value for the coefficient of kinetic friction but least amount of cutting stress and cutting temperature during HEA deformation suggesting this orientation to be better than the other orientations for its improved manufacturing.

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