Finite Element Analysis On Mechanical Response Of Microscale Films

Film-substrate materials are used widely in many project fields.therefore,improved-performance to material surface and film mareial are importantdevelopment aspects in material science field recently. There is an importantsignificance to resesch it. But good cohesion between film and substrate material isthe essential condition to exploit the advantages of films. Cohesion strength betweenfilm and substrate material is critical index, which guarantee to satisfy the requests ofmechanical, physical and chemical performances.The most major result of film disjuncture is that the accumulation of plasticdeformation in the film generates the cracks under normal force and tangential force.The oversize strength between the interfaces is the major factor for film disjuncture.Now the cohesion of between film and substrate material is measured by scratchingexperiment. We have difficult to found the corresponding mechanical model becauseof complex mechanical relations.According to scratching experiment and research findings, a new mechanicalmodel applied to strain-stress mechanics response is founded, which imitate to thebeginning process of scratching test. Firstly, applied to a normal force which makescontact between coat and indenter, then normal force and tangential force together areapplied to the coat and make the coat have a moving tendency to the right.In the paper, numerical model is simplified to a plane strain problem. Athree-dimensional Vickers indenter is simplified to a two-dimensional wedge indenterwith an angle 136°. It is assumed that the indenter is made of rigid material, the filmand substrate are made of isotropic elastic-perfectly plastic material, and Mises yieldcondition is obeyed. The friction between indenter and film is considered.The needed computing programs are developed on the platform FEPG (FiniteElement Program Generating System) software. Incremental iterative method is usedbecause of the nonlinear problem.Based on the model and program, we calculate the film stress filed in thecondition different thickness film with the same substrate, different substrate with thesame film and different normal force separately, and It indicates that stress of TiN filmis related with substrate material, film thickness, normal force and tangential. Thecalculation results provide reference evidence to theoretical analysis of scratching test.In the process of long-time use, coat can cause the crack because of work fatigue,especially on the interfaces. In addition, tiny crack can be generated during themanufacture. Crack propagation leading to decohesion or delamination is one of themajor failure. Evaluating coat should consider the crack propagation on the interfaces,therefore, in the paper the influence on length and wide on TiN/HSS single film, thecrack position influence on TiN/Au/HSS film are analyzed and It manifest that thestresses of film are influenced with cracks.