An Assessment of a Titanium Alloy for Supersonic Transport Operations

An assessment is given of the materials problems and implications regarding the use of Ti-8Al-1Mo-IV alloy sheet for the skin of a supersonic transport. Although the assessment of this alloy in the duplex annealed condition is generally favorable, several questions remain unanswered and new ones continue to arise. The seriousness of the salt stress corrosion problem at 500 F and above under flight conditions cannot be predicted on the basis of current laboratory corrosion tests. A new potential stress corrosion problem at ambient temperatures in the presence of cracks and salt water requires investigation. The ability to withstand a 30,000-hour exposure at 550 F without undue degradation of the material or welds will remain doubtful until more long-time data are available. The substitution of a more corrosion-resistant and stable titanium alloy in the tension critical areas of the structure may prove advisable.