SPF Characteristics of Fine Grain TIMETAL®54M Sheets

Ti-5Al-4V-0.6Mo-0.4Fe alloy (Ti-54M) is a new alloy developed at TIMET. The alloy exhibits superior machinability in most of machining conditions and strength comparable to that of Ti-6Al-4V. In the previous conference (AeroMat 2009), SPF (Superplastic Forming) properties of Ti-54M sheets were presented. A total elongation exceeding 500% was observed at temperatures between 1400ºF (760°C) and 1600ºF (871°C) at a strain rate of 10^-3/S. Steady stress-strain curves in tensile tests, indicating the occurrence of grain boundary sliding, were observed at temperatures between 1400ºF (760ºC) and 1550ºF (843ºC) at a strain rate of 5x10^-4/S. It is well understood that primary alpha grain size is the most influential factors that enable SPF behavior at lower temperatures and higher strain rates. An attempt was made to produce ultra-fine grain (UFG) Ti-54M sheets in a laboratory scale. SPF properties of the sheets were evaluated in accordance with ASTM 2448-06. The sheets exhibited SPF behavior at the temperatures as low as 1300°F (704°C) at a strain rate of 5x10^-4/S. This paper will discuss SPF capability of fine grain Ti-54M sheets compared with regular grain Ti-54M and Ti-64. The effects of strain rate, temperature and microstructure on flow behaviors and m-values, as well as micro structural development during SPF tensile tests will be presented and discussed.