The Study Of Mechanical Properties Of Ti-si-n Superhard Nano-composite Coating With The Finite Element Simulation

The research reported in the paper is a part of the project of National Natural Science Foundation of China (50845065),the project of Education & Science Research Foundation of Inner Mongolia(NJ06077) and the project of Natural Science Foundation of Inner Mongolia (2009MS0812). The main purpose is to study the mechanical properties, including the stress-strain relation and yield strength, of Ti-Si-N superhard nanocomposite film with the FEM simulation of nanoindentation measurement process. A new method of the determination of material yield strength is presented in the study. Using this method, the mechanical properties of TiN and Ti-Si-N films are investigated.In this project, we applied ABAQUS to simulate the nano-indentation process of TiN and Ti-Si-N films and fitted the measured curve of force-displacement. The fitting process includs the following steps:1. To extract the corresponding data of the force-displacement curve obtained in the nanoindentation measurement;2. To obtain the stress-strain data via calculation;3. To build the FEM simulation model:geometric model consists of the Berkovich indentor and the measured TiN or Ti-Si-N block; then input the calculated stress-strain data as the properties of the block and setup boundary conditions of the block and the assembly relation of the indentor and the block; after that define loading steps and conduct the FEM simulations;4. To use different yield strength to FEM simulations and find out closed results to the measured force-displacement curve, bywhich determine the yield strength value;5. To use the determined yield strength and different strain values in FEM simulations to fit the measured force-displacement curve further. Ultimately, fix on the appropriate strain value.Using the above methods, the fitting of measured force-displacement data of the TiN and Ti-Si-N coatings with FEM simulations has achieved good result.By comparing and analysing the stress-strain, equivalent plastic strain curves and the hardness calculation of TiN and Ti-Si-N coatings, it is determined that the yield strength of TiN is about 12GPa, but that of Ti-Si-N is as high as 24GPa. The results show that the plastic properties of materials can be obtained by the method of finite element simulation of nano-indentation process. Therefore, the method presented in this paper is useful for the plastic property study of thin films.