Microstructure and creep deformation of a near beta titanium alloy 'beta-CEZ'

The relationship between titanium alloy processing, structure and propertie s received great attention in recent years. The aim of this paper is to det ermine the influence of the microstructure of a titanium alloy on its creep properties at intermediate temperature. A pronounced influence of the micr ostructure. quantified by image analysis, on the steady-state creep rate wa s found. Structures exhibiting large values of length, width, surface and/o r perimeter of the primary intragranular alpha phase (alpha(p)) and thus lo w values for the total interfacial area between the alpha(p) and beta matri x, show low creep strength at 400 degrees C. In addition, the influence of various parameters such as the texture of the alpha phase, the size and the morphology of the alpha phase (at prior beta grain boundaries and secondar y alpha phase) and the prior beta grain size were investigated. The effects of temperature and stress level on the creep response of the alloy were in vestigated in the temperature range of 400 to 470 degrees C. The stress dep endence of the steady-state creep rate indicates that an increase in temper ature introduces a gradual decrease in the stress exponent n and a change o f creep mechanism at 400 to 450 degrees C, depending on the stress level. T he apparent activation energy of creep was determined for different stress levels. Transmission electron microscopy observations of deformed dislocati on structures developed during creep are used to interpret creep properties , and deformation mechanisms are proposed for the primary and secondary int ragranular alpha phases. (C) 1999 Elsevier Science S.A. All rights reserved .