Abstract
The interfacial structure of ReB2/TaN multilayers at varied modulation periods (Λ) and modulation ratios (tReB2:tTaN) was investigated using key experiments combined with first-principles calculations. A maximum hardness of 38.7 GPa occurred at Λ = 10 nm and tReB2:tTaN = 1:1. The fine nanocrystalline structure with small grain sizes remained stable for individual layers at Λ= 10 nm and tReB2:tTaN = 1:1. The calculation of the interfacial structure model and interfacial energy was performed using the first principles to advance the in-depth understanding of the relationship between the mechanical properties, residual stresses, and the interfacial structure. The B-Ta interfacial configuration was calculated to have the highest adsorption energy and the lowest interfacial energy. The interfacial energy and adsorption energy at different tReB2:tTaN followed the same trend as that of the residual stress. The 9ReB2/21TaN interfacial structure in the B-Ta interfacial configuration was found to be the most stable interface in which the highest adsorption energy and the lowest interfacial energy were obtained. The chemical bonding between the neighboring B atom and the Ta atom in the interfaces showed both covalency and iconicity, which provided a theoretical interpretation of the relationship between the residual stress and the stable interfacial structure of the ReB2/TaN multilayer.
Highlights
Hard and wear-resistant coatings are increasingly used to reduce the material losses or to increase the lifetime of tools and machine parts
We conducted a preliminary theoretical study of ReB2/tantalum nitride (TaN) multilayers, in which only the interface of the TaN(100)/ReB2(001) was chosen to calculate the interfacial structure, which showed that the B-N interface had a stronger covalent bonding [27]
Along with atomistic simulations of the interface, this paper presents new data and more in-depth interpretation on the hardness enhancement of ReB2/TaN multilayers
Summary
Hard and wear-resistant coatings are increasingly used to reduce the material losses or to increase the lifetime of tools and machine parts. Thin-film structures consisting of alternating nanoscale multilayers have been attractive subjects in the area of protective coatings due to their extraordinary properties, such as their enormous hardness, which cannot be obtained in uniform bulk materials or in monolithic coatings of the constituent materials. We conducted a preliminary theoretical study of ReB2/TaN multilayers, in which only the interface of the TaN(100)/ReB2(001) was chosen to calculate the interfacial structure, which showed that the B-N interface had a stronger covalent bonding [27]. In addition to studying the experimental changes in the mechanical properties, modulation period, and modulation ratio, we focused on the hardness mechanism and the relationship between the mechanical properties, residual stress, and interfacial structure using first-principles calculations that are based on density functional theory (DFT). For the first time (to the authors knowledge), we calculated and found the contribution of the interfacial energy, adsorption energy, and the interfacial stability to the residual stress release by controlling the appropriate interfacial structure
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