Microstructural banding in thermally and mechanically processed titanium 6242
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Ti-6Al-2Sn-4Zr-2Mo-0.1Si coupons were shaped by repeated cycles of heating (to 954 °) and hammer or press forging followed by a solution anneal that varied from 968 to 998 °. The coupons were originally extracted from billets forged below the beta transus (1009 °) and slow cooled to ambient temperatures. Macroscopic and microstructural banding is observed in some forged and solution annealed coupons. The microstructure consists of elongated “platelets” of primary alpha. More significant banding is observed subsequent to annealing at lower temperatures (968 °), whereas subsequent to higher annealing temperatures (998 °) much less microstructural banding is present. About the same level of banding is observed in hammer forged coupons and press forged coupons. The observation of these bands is significant, because these may lead to inhomogeneous mechanical properties. Specifically, some types of banding are reported to affect the high-temperature creep properties of this alloy. Classically, banding in Ti6242-0.1Si has been regarded as a result of adiabatic shear, chill zone formation, or compositional in homogeneity. High- and low-magnification metallography, electron microprobe analysis, and micro-hardness tests were performed on forged and annealed specimens in this investigation. The bands of this study appear to originate from the microstructure that consists of the forged billet of elongated primary alpha. The deformation of the extracted coupon is neither fully homogeneous nor sufficiently substantial, and the coupon is only partly statically restored after a solution anneal. Areas not fully restored appear as “bands” with elongated primary alpha that are remnant of the starting billet microstructure. Therefore, a source of banding in Ti- 6242- O.1Si alloy additional to the classic sources is evident. This type of banding is likely removed by relatively high solution treatment temperatures and perhaps greater plastic deformation during forging.
KeywordsShear Band High Annealing Temperature Adiabatic Shear Solution Anneal Adiabatic Shear Band
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