haracterization of the interphase in epoxy/aluminum bonds using atomic force microscopy and a nano-indenter

It is believed that a transition region may exist between the bulk adhesive and the adherend, which would play an important role in the performance of the joint. Epoxy/aluminum joints were studied using a nano-indenter and an atomic force microscope (AFM). Some samples were based on direct bonding of aluminum specimens with the epoxy adhesive and some used aluminum samples pre-coated with a softer epoxy system to simulate a soft interphase. The topography of indented samples was measured using AFM and the image was used to define the indentation positions. Results were interpreted in terms of three types of interactions of the indenter with the sample in the interface region: (a) direct contact of the indenter with both phases during indentation, (b) contact of the indenter with a single phase but for which the indentation response was directly affected by the adjacent phase and (c) contact with a modified resin phase near the interface the: 'interphase'. The importance of sample surface preparation was also studied. Results showed that polishing the surface often resulted in formation of ridges and troughs near the interface which resulted in artifacts, which could be interpreted as indicating the presence of a soft interphase. © VSP 2005.