Investigations on the mechanical behaviour of rough surfaces of TiNi thin films by nano indentation studies

Nano hardness tests were conducted on TiNi thin films deposited by sputtering of a mosaic target comprising of segments of Titanium and Nickel. The composition of the films was determined by alpha particle back scattering (RBS). Surface topography of the films, imaged using an AFM, revealed high surface roughness, comparable to the indentation depth, leading to a large scatter and erroneous results from the indentation data. The objectives of the present investigation were (i) to extract the actual hardness of the film from the nano indentation data and (ii) to analyse the contact mechanisms during penetration of the indenter into the film by applying a statistical model of the surface roughness. Various mechanical parameters pertaining to the indentation process, namely, the point of first yield and the plasticity index of the film after deformation have been calculated. Variation of the deformation behaviour of the films as the asperity sizes increase is also reported.