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

The relationship between titanium alloy processing, structure and properties received great attention in recent years. The aim of this paper is to determine the influence of the microstructure of a titanium alloy on its creep properties at intermediate temperature. A pronounced influence of the microstructure. quantified by image analysis, on the steady-state creep rate was found. Structures exhibiting large values of length, width, surface and/or perimeter of the primary intragranular alpha phase (alpha(p)) and thus low values for the total interfacial area between the alpha(p) and beta matrix, 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 secondary 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 investigated in the temperature range of 400 to 470 degrees C. The stress dependence of the steady-state creep rate indicates that an increase in temperature introduces a gradual decrease in the stress exponent n and a change of creep mechanism at 400 to 450 degrees C, depending on the stress level. The apparent activation energy of creep was determined for different stress levels. Transmission electron microscopy observations of deformed dislocation structures developed during creep are used to interpret creep properties, and deformation mechanisms are proposed for the primary and secondary intragranular alpha phases. (C) 1999 Elsevier Science S.A. All rights reserved.