A new proposed parameter related with atomic size effect for predicting hardness of HEA coatings

The new parameter epsilon we proposed in this study is to be more conducive to the hardness design of high-entropy alloy coatings. Here, the parameter epsilon is defined as the ratio of the atomic size mismatch to the atomic stacking mismatch. This parameter can be used as the criterion for measuring the magnitude of lattice distortion caused by the atomic size effect, which reveals the influence of the atomic size effect on the hardness of the alloy. We collected nearly 100 groups of on high-entropy alloy coatings in order to verify the feasibility of parameter epsilon, and to analyze the relevant data from available literatures by using the parameter epsilon. We found that the hardness value of the high-entropy alloy coatings showed monotonicity with the epsilon increased. When epsilon < 6.4, the phase structure of the coating is mainly fcc phase, the increase in hardness of the coating is smaller with the increments of epsilon. The opposite of bcc phase as the main phase for epsilon > 6.4, hardness value of the coating escalates with the increase of parameter epsilon. Based on this finding, it is suggested that the parameter epsilon can then be used to design a high-entropy alloy coatings with the desired hardness. (C) 2020 Elsevier B.V. All rights reserved.