Influence of Grain Size and Microstructure on Oxidation Rates in Titanium Alloy Ti-6Al-4V Under Superplastic Forming Conditions

Ti-6Al-4V (Ti-6-4) sheets of two different grain sizes were exposed to time and temperature conditions representative of superplastic forming (SPF). The influence of SPF conditions on oxidation rates was evaluated in terms of weight gain, α-case depth, and microhardness profile. Differences in the response are related to the difference in grain size between the two lots of Ti-6-4. Fine grain Ti-6Al-4V exhibits faster oxygen diffusion in all three areas examined in this study, weight gain, α-case thickness, and increased microhardness depth. The differences were found to be significant relative to diffusion analysis and processing during manufacturing. Results from this work support reduced temperature SPF using fine grain material and the accompanying benefits in manufacturing superplastic parts.