AVS 46th International Symposium
    Applied Surface Science Division Thursday Sessions
       Session AS-ThA

Paper AS-ThA10
Surface Analysis Characterization of Titanium/Sol-Gel/Polyimide Adhesive Systems

Thursday, October 28, 1999, 5:00 pm, Room 6A

Session: Polymer Surfaces, Films, and Interfaces
Presenter: J.T. Cherian, Boeing Materials Technology & University of Washington
Authors: J.T. Cherian, Boeing Materials Technology & University of Washington
D.G. Castner, University of Washington
Correspondent: Click to Email
Bonded titanium alloys are being evaluated for use at an operating temperature of 175°C. Determining the locus of failure for bonded titanium lap-shear specimens is part of a larger effort to develop durable, environmentally safe surface treatments for titanium alloys. Surface-treated titanium alloy (Ti-6Al-4V, Ti3Al-2.5V, and Ti15V-3Al-3Cr-3Sn) plates are bonded in a standard lap-shear specimen configuration and exposed to temperature for specified intervals. The lap-shear bond joint consists of two etched titanium panels that are coated with a silicon and zirconium containing sol-gel, primed with a polyimide, and then bonded together with adhesive and supporting scrim material. The lap-shear specimens are tested for overall strength and failure modes. Specimens with cohesive failure modes were examined with ESCA and ToF SIMS to determine the composition of the bond joint failure layer. Although the failure was located closer to the sol-gel/polyimide interface than to the Ti/sol-gel interface, ESCA and ToF SIMS analysis revealed that the actual location (sol-gel, primer, etc.) of the failure varies from spot to spot across a given specimen. SEM analysis suggests that the rough surface of the titanium oxide introduces stress at the interface and promotes the non-uniformity of the failure regimes. A model system is being used to investigate the interfacial bonding chemistry between the sol-gel and the polyimide primer. Pure titanium is deposited onto silicon wafers to create a smooth titanium substrate. Smooth, thin layers of sol-gel and polyimide coatings are then spun onto the Ti surface. AFM is used to measure the surface roughness of each layer. ESCA analysis in conjunction with pentafluorobenzaldehyde derivatization is used to follow the changes in the bonding chemistry at the sol-gel/polyimide interface as the sample is cured.