Evaluation of the Adhesive Bonding Processes Used in Helicopter Manufacture. Part 3. Development of Improved Titanium Surface Treatments

摘要

Studies were made to determine whether rutile-free, anatase-containing oxide layers on CP titanium and titanium 6-aluminum, 4- vanadium alloy, could transform to rutile- containing layers on aging. Scanning electron microscope observations and electron diffraction showed that rutile could be detected in the oxide layers on some aged specimens which had been adhesively bonded, stressed, and exposed to high ambient temperatures and relative humidities. Since these specimens had been prepared using a phosphate-fluoride treatment known to give anatase-containing layers, it appeared that the conversion of anatase to rutile could take place in adhesively bonded joints. Further, it appeared that the anatase-rutile conversion was associated with bond failure. In attempts to stabilize anatase in oxide layers against conversion to rutile, the phosphate-fluoride treatment was modified by inclusion of salts of likely stabilizing ions in various steps of the treatment. In some cases, the contents of the ions in the surface were markedly increased, and sometimes the morphology of the surface oxide layer was changed. On the basis of extended times to failure of stressed joints made using some of the modified surface treatments, it appeared that these surface treatments were beneficial. (Author-PL)