Mechanical Properties Of Tough Films On Tough Substrates By Nanoindentation

With the development of science and technology, thin films and coatings have been applied by peopled more widely and widely. Because the mechanical properties of thin films or coatings can play an important role in the failure and life and it is crucial to determine the mechanical properties. As a technique to evaluate the mechanical properties of thin films or coatings, nanoindentation test is in the popularity for its high displacement resolutions, ultra low load and the capability of continuous measurement. In the master thesis, explicit relationships between the indentation loading-unloading parameters and material properties of tough films on tough substrates have been established through dimensional and extensive finite element analysis.In the Introduction, the application of thin films and the development of the measurement techniques of the mechanical properties were reviewed. The background and development of nanoindention test were interpreted detailedly.Firstly, tough film/tough substrate systems were classified as isotropic tough without transition layer film/tough film, FGM tough film/tough film and isotropic tough film with transition layer/tough substrate systems. Dimensional analysis was applied to derive the forms of indentation responses of tough film/tough substrate composite by Berkovich indenter. Then, using these forms associated with finite element calculation, a relationship between the mechanical properties and the responses of the material was obtained. By using Berkovich nanoindentation loading-unloading curves of Ni films with three thicknesses 1.7, 2.5 and 4.0um electrodeposited on mild steel substrates, the strain-stress relationships of Ni films were obtained. The yield strengths of the films are higher than that of the Ni bulk and the yield strength increases with the film thickness decreasing. The result was rechecked with uniaxial tensile test of Ni film electrodeposited on a mild steel substrate and they agreed reasonably well with that evaluated by the nanoindentation test. At last, explicit relationships between the indentation loading-unloading parameters and materials properties of FGM tough films or tough film with transition layer on tough substrates have been established through dimensional and extensive finite element analysis.