Study On Mechanical Behavior Of Coating-substrate Based On Finite Element Modeling

In this work, numerical methods based on finite element modeling (FEM),especially in combination with the experimental nano-indentation data, have been successfully used to analyze complex stress-strain property of SiCN coating with high temperature resistance. Theoretical treatments are limited in the case of elastic-plastic problems because the elastic-plastic stress fields of tested material around the indenter are complex. Numerical methods, like finite element method, are widely used to analyze elastic-plastic indentations beneath a pointed indenter in nano-indentation test.Finite element simulation can offer many advantages. With this method, the time spent for the experiment can be reduced. A large scale finite element commercial codes, can provide simulation environment for various physical models of indenter tips, films and substrates. In some previous work, the numerical results showed satisfactory agreement with the experimental data. The method can also describe the failure and stress-strain distribution in the coated system, crack nucleation and propagation during nano-indentation.The finite element model of coating-substrate system is established and the elastic modulus of the tested material is measured by nano-indentation test. By varying input stress-strain properties of SCN coating, different load-displacement curves can be obtained from finite element simulation. Comparing FE load-displacement curves with the experimental one, the best match should indicate the correct input of material properties. The last load-displacement curve is regarded as the SiCN coating at the 90nm nano-indentation depth. On this foundation, the stress-strain distribution relationship of coating-substrate is researched under the different nano-indentation depths of SiCN coating. The result shows the nano-indentation depth is smaller than 10% of the coating thickness. Otheirwise, the substrate influences the measurement and evaluation of coating. Finite element method can also get the mechanical properties of coating-substrate system when the nano-indentation depth exceeds a certain value, however the nano-indentation test can not achieve the goal under this circumstance. Secondly, the study on the bonging strength of multilayer coatings is researched by using FEM. It is found that adding appropriate transition layer is beneficial to increase the bonding strength between coating and substrate so that prolonging the service life of the coating. In the last, the deformation and failure of single layer and multilayer coatings are analyzed by extended finite element method(XFEM). The result shows that the coating-substrate system with the transition layer has better ability to resist failure.