The durability of adhesively-bonded Ti-6Al-4V

The durability of chromic acid-anodized Ti-6Al-4V alloy, adhesively-bonded with FM-5 supported polyimide adhesive has been studied. The performance te sts compared titanium samples that had been thermally treated and bonded, a nd samples that were bonded and thermally treated. Following the thermal tr eatment, the durability was examined (1) by immersing wedge-type specimens in boiling water and measuring the crack growth and (2) by measuring the la p shear strength for single lap specimens. In the wedge tests, failure occu rs within the adhesive for specimens treated at temperatures below 371 degr eesC for less than one hour. For treatments at higher temperatures and for longer periods of time, failure occurs within the anodic oxide. From the la p shear tests, the principal finding is that the lap strength decreases wit h increasing treatment time at constant temperature and with increasing tem perature at a fixed time. For the lap specimens, failure occurs to a greate r extent within the oxide as the treatment time and temperature increase. S urface analysis results indicate the formation of an aluminum fluoride spec ies. It is reasoned that the formation of fluorine-containing materials wea kens the oxide and promotes failure within the anodic oxide.