Nanoscale mechanical characterization of the effect of thermal aging on titanium/PETI-5 adhesive interface properties

Titanium substrates coated with silicate/zirconate sol-gel and plasma sputt ered chromium have been adhered using a combined PETI-5 polyimide psuedo-th ermoplastic primer/adhesive system. Composite laminates were exposed to the rmal aging up to 2000 hours at 194 degreesC and subsequently nanoindentatio n testing was performed across each interface to determine material modulus degradation and plastic deformation changes. The procedure to analyze comp lex interfaces using nanoindentation are explained in detail including expe rimental set-up, analysis, and imaging; for example, inhomogeneities at the interface mandated that both low loads (as low as 25 muN) and a 90 degrees cube-corner diamond tip be utilized to obtain sub-micron resolution. Therm al aging resulted in an increase in PETI-5 primer and adhesive modulus by 1 5% and upwards of 30%, respectively, and the sol-gel modulus increased by a pproximately 10%. An exposure level at 1000 hours showed a 20% increase in the chromium modulus. Large increases in plastic deformation were observed in the polymeric materials likely due to chain embrittlement.