Finite element analysis of residual stress and interlayer in hard coating/interlayer/soft substrate system during nanoin
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Paul K. Chub) School of Physics and Materials Science, City University of Hong Kong, Kowloon, Hong Kong, People’s Republic of China (Received 27 September 2007; accepted 30 January 2008)
The mechanical properties of thin films are frequently evaluated using nanoindentation. The finite element method (FEM) is very effective for investigating the stress and strain fields of the film–substrate system during nanoindentation. However, the role of residual stress and the thin interlayer between the film and substrate is not well known, especially when the hard coating/interlayer/soft substrate are considered together. In this work, the FEM is used to investigate the load-displacement behavior of the hardness of the hard coating/interlayer/soft substrate system. The load–displacement process is simulated, and the effects of different residual stresses and interlayer thicknesses are discussed.
I. INTRODUCTION
Coatings are widely used to improve surface mechanical properties, such as wear resistance, friction coefficients, and hardness, and materials, such as TiN, TiC, Al2O3; more recently, diamond and diamondlike carbon have been used commercially. To investigate the reliability and mechanical properties of coatings, nanoindentation is frequently used. By using different indentation loads to access various depths, an indentation curve can be generated to determine the mechanical properties of the coating, such as hardness and elastic moduli.1 However, if the coating is too thin, the mechanical properties may not be disclosed accurately because the substrate interferes with the measurement. Moreover, it is difficult to obtain an analytical solution because indentation can be highly nonlinear due to large deformation, strain, the nonlinearity of the materials, and contact. To overcome these problems, numerical analysis has been used. For instance, Ma and Xu2 used the finite element method (FEM) to study the indentation of aluminum films on silicon using a rigid spherical indenter, and the relationship between the mechanical properties of the film and the specified values of the load–displacement curve were
Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2008.0171 1358
J. Mater. Res., Vol. 23, No. 5, May 2008
obtained. Zheng and Sridhar3 adopted the FEM to perform an accurate numerical analysis of the normal indentation of an elastic–plastic layer by means of a rigid sphere, and the effects of the yield strain of the substrate on the onset of plasticity were investigated. The effects of the mechanical properties, such as elastic modulus, yield strength, strain hardening of the films, and residual stress on the indentation response, were investigated using the FEM.4,5 Furthermore, the stress, fracture, and delamination during indentation of a hard elastic film on an elastic–plastic substrate were also studied by some other researchers using the FEM.6–8 Lichinchi et al.9 verified the feasibility of the FEM by simulating the nanoindentation progre
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