Atomistic Simulation of Scratch behavior of Ceramic/Metal (CerMet) nanolaminates
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Atomistic Simulation of Scratch behavior of Ceramic/Metal (CerMet) nanolaminates !
Adnan Rasheed, Iman Salehinia Department of Mechanical Engineering, Northern Illinois University, DeKalb, IL 60115, USA ABSTRACT: !
The promise of nanocomposites lies in their multi-functionality, the possibility of realizing unique combinations of properties that are not attainable in traditional materials. Ceramic/metal multilayers (CMMs) are one such unique combination that are becoming increasingly popular among researchers today. The idea is to combine the superior properties of ceramics like hardness and strength with favorable properties of metal such as ductility. Materials with these characteristics have potential for engineering applications such as highly efficient gas turbines, aerospace materials, automobiles, protective coatings, etc. Molecular dynamics atomistic simulations were performed to study the scratch behavior of different models of niobium carbide (NbC)-niobium (Nb) multilayers. The layer thicknesses were varied and the coefficient of friction was calculated at various depths of indentation. The deformation mechanisms were investigated to explain the observed mechanical behavior of the models under scratching. Model with the lowest metal/ceramic thickness ratio (2nm NbC/2nm Nb) showed the highest hardness, highest scratch resistance, and also highest friction coefficient. However, this model also showed the highest materials removal rate.
INTRODUCTION: !
Ceramic/metal multilayers (CMMs) have shown promising mechanical, physical and chemical properties, making them practically useful in a wide range of temperatures, mechanical loadings and environmental conditions [1]. Experimental [2-4], theoretical [5-8] and atomistic [9-12] methods have been used to characterize the mechanical behavior of CMMs under various types of loading and environmental conditions. The dominant deformation mechanisms including dislocation nucleation from the interface, dislocation propagation, dislocation deposition on the interface, and co-deformation of metallic and ceramic layers were investigated. CMMs are particularly of interest for applications with extreme tribological conditions [13-16]. By alternating hard and soft materials, the hard layers can slide over each other preventing building-up the residual stresses [13,15,17,18]. Furthermore, interfaces between the metallic and ceramic layers can act as sites for energy dissipation due to their low shear strength, and as a result they block the incoming cracks or deflect them [5,19]. Wear and scratch tests on TiN/Ti [14,20] and SiC/Al [21] have shown higher scratch resistance and fracture loads for ceramic/metal nanolaminates comparing to their individual metallic or ceramic counterparts. Lackner et al. [14] performed a comprehensive investigation of the tribological behavior of TiN/Ti multilayers with different bi-layer period and thickness ratio. The deformation mechanisms under static and dynamic mechanical loading were explained. Reduction in wear was reported for samples w
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