Durability of adhesive bonding of titanium in radiation and aerospace environments

Abstract

In this investigation, attempts have been made at understanding the effects of high-energy radiation, low and high temperatures on adhesive bonding of titanium (ASTM F 67–95 Grade 2). Two titanium sheets are joined by a ceramic adhesive (Resbond™ 907 GF). The service temperature of this adhesive ranges from –185 to +1290 °C and, in addition, this adhesive has excellent resistance to most acids, alkalies, solvents, corrosive agents and fire, and, therefore, is extremely useful for aerospace applications. Prior to joining, the surfaces of the titanium sheets are mechanically polished by wire brushing, cleaned by isopropanol and then modified by sodium hydroxide anodization. First, to determine the joint strength under ambient conditions, tensile lap shear test are performed according to the ASTM D 5868-95 standard. Then the joints are exposed to aggressive chemical environments. It is observed that the joint strength decreases drastically for those joints prepared without modifying the titanium surface by sodium hydroxide anodization. However, the titanium surface modified by sodium hydroxide anodization and joined are able to retain about 70% of their strength. These joints are then irradiated for 6 h at a dose rate of 37 kGy/h in the pool of a SLOWPOKE-2 nuclear reactor, which produces a mixed field of thermal and epithermal neutrons, energetic electrons and protons and gamma rays. It is observed that under this exposure, the joint strength remains almost unaffected. In order to simulate the service conditions of aerospace applications, the joints are also exposed to low temperature (−80 °C) and elevated temperature (+500 °C) for 100 h. It is observed that in these cases, the joints retained the strength of about 95% in respect to the strength of the joint tested under ambient conditions. Failures of the joints are observed as primarily cohesively within the adhesive. Therefore, this adhesive bonding of titanium is a very good candidate for structural applications in aerospace.