Isothermal α" formation in β metastable titanium alloys

Thanks to time resolved high energy X-ray diffraction, isothermal decomposition of beta metastable phase was studied, directly after solution treatment in the beta temperature range, for temperatures ranging from 300 to 450 degrees C for two beta metastable alloys (Ti 17 and Ti 5553). The formation of an orthorhombic alpha" phase is clearly identified at the beginning of the transformation whatever the alloy studied. If transformation occurs at the higher temperature an evolution of alpha" is observed toward the hexagonal alpha phase. The phase amounts and the mean cell parameters of each phase were quantified by the Rietveld refinement method. The obtained cell parameters evolutions and the orthorhornbicity of alpha" are discussed. Moreover, the orthorhombicity of alpha" compared to that obtained for stress induced martensite may indicate a slight partitioning of solutes in isothermal alpha". (C) 2012 Elsevier B.V. All rights reserved.