On the correlation of microhardness with the film adhesion for “soft film on hard substrate” composite system

Composite systems of monolayered electrodeposited Ni and Cu thin films (5-10 μm) on monocrystalline Si wafers and 50 μm-thick electrodeposited Ni film as the substrates were fabricated. On the basis of their difference in hardness, these systems can be thought of as “soft film on hard substrate” composite systems. Adhesion of electrodeposited films on different substrates was investigated by Vickers microindentation hardness testing. Strong adhesion corresponds to extended plastic deformation zone at the film/substrate interface. Interfacial tension effects contribute to the measured hardness. Composite hardness models of Chicot-Lesage (C-L) and Chen-Gao (C-G) were applied in order to investigate the influence of adhesion on microhardness test results. When adhesion exists between the film and the substrate, the critical reduced depth (the ratio between the radius of the plastic zone beneath the indent and the indentation depth) increases. Microhardness measurements are useful tool for assessment and quantification of the film/substrate interface strength