Abstract
A three-dimensional (3D) scratch model is proposed to investigate the effects of yield strength of both coatings and substrates. With the help of combined Coulomb and plastic friction, the obtained results comprehensively interpret the experimental phenomena in most metals that with the growth of hardness after heat treatment the scratch friction coefficient (SFC) increases. This interpretation could not be done before. Scratch tests on the surface with or without the coating are discussed. Without the coating the SFC increases due to the decrease of the area with plastic slippage and/or the increase of friction stress during the increase of the yield strength in the material. With a softer substrate the friction stress decreases but the SFC increases, which is caused by the growth of the entire contact area and surface deformation. Conversely, with a stronger substrate the SFC decreases due to an intensified plastic slippage. The obtained results pave a new way to understanding the effects of yield strength on scratch tests, interpret experimental phenomena, and should be helpful for an optimum design in experiments.
Highlights
There has been an increased interest in the application of surface coatings by changing the surface properties independently of the bulk material [1−4]
A 3D scratch model is proposed to study the effects of yield strengths in both coatings and substrates by using finite element method (FEM)
The obtained results help in better understanding the effects of yield strength on scratch tests and to interpret experimental phenomena, and should be helpful for an optimum design in experiments
Summary
There has been an increased interest in the application of surface coatings by changing the surface properties independently of the bulk material [1−4]. Previous FEM results based on the traditional Coulomb friction failed to explain it and even displayed an opposite trend; with a growth of yield strength the scratch friction coefficient reduces One of the goals of this paper is to study the effects of yield strength in the surface coating and further interpret the experimental phenomenon in detail. The yield strengths in both substrate and coating play an important role in tribological performances of the material surface. Another goal is to investigate the effects of the combined yield strengths of the substrate and coating, which will give completely distinct viewpoints from previous FEM results [5−10, 13]
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