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Published online by Cambridge University Press: 26 February 2011
Ti-Al-Cr ternary and Ti-Al-Cr-Nb quaternary alloys have been studied as a function of initial purity and added interstitial content. Using strict clean processing together with either ultra high purity or commercial purity alloys, the effects of interstitial elements (essentially O, but also C and N) on microstructure and hardness, yield stress and fracture strain have been studied for both fully lamellar microstructures and duplex microstructures. The results are clear and similar trends are observed : as long as they do not precipitate, these stabilise the lamellar microstructure and affect the kinetics of the α-γ phase tranformation, leading to a higher than equilibrium value for the α2 phase for continuous cooling. Both the lamellar spacing and the α2 phase fraction correlate with increased hardness and yield stress, and also with decreasing fracture strain. The effects are significant.