BS in Materials Engineering
Materials Engineering Department
Forty-eight subsize round-bar tensile samples (ASTM E8) were machined from 3-in-thick forgings of Ti-6Al-4V. Half of these samples were cut so the axis aligned with the longitudinal (LG) direction of the forging, the other half were cut to align with the transverse (LT) direction. Four samples from each direction were subjected to one of six heat treatments so that a total of eight samples received each treatment. Annealed samples were held at 1350°F for two hours, then air cooled. Solution treated and aged (STA) samples were solution treated at one of five temperatures between 1785°F and 1435°F for one hour and then water quenched after a 25 second quench delay in air. Following quenching, all STA samples were aged for 6 hours at 990°F, then air cooled. Prior to tensile testing, the samples were sent back to Weber Metals for chemical milling to remove the brittle alpha-case surface layer formed during heat treatment. A polymer coating was applied to the samples’ threaded ends so only the gage length would be milled, and any oxide present was sanded off to avoid preferential etching. Tensile tests showed anisotropy primarily in Tensile strength with the LT direction testing 3-7 ksi higher than the LG direction. A general linear model found a significant difference of Tensile strengths between directions in all heat treatments except for STA 1, which had the highest solution treating temperature. A difference of about 7 ksi was also found between STA 5 samples in Yield strength. No anisotropy was observed in Elongation. It was concluded that higher solution-treating temperatures decreased anisotropy by transforming the textured alpha into beta, effectively erasing any alignment. It was also concluded that the LT direction is stronger than the LG due to non-preferred slip systems being the primary mechanism of deformation.