Creep behaviour and creep microstructures of a high-temperature titanium alloy Ti-5.8Al-4.0Sn-3.5Zr-0.7Nb-0.35Si-0.06C (Timetal 834) - Part 1. Primary and steady-state creep

The tensile creep behaviour of the high-temperature near alpha -Ti alloy Ti -5.8Al-4.0Sn-3.5Zr-0.7iNb-0.35Si-0.06C (Timetal 834) with a duplex microstr ucture has been extensively investigated in the temperature range from 500 degreesC to 625 degreesC and the stress range from 100 to 550 MPa. Both pri mary and secondary creep are being considered. The results of the primary c reep are analysed in terms of the dependencies of stress on strain (strain hardening) and on strain rate (strain rate sensitivity). It is shown that t he strain-hardening exponent depends on temperature, and takes values betwe en 0.5 for 500 degreesC and 0.33 for higher temperatures; this would give a dependence of the primary creep strain of sigma (2) and sigma (3). The str ain rate exponents obtained in both primary and secondary creep have been f ound to be similar; this is also the case for the activation energies. It i s thought that, in the stress and temperature range investigated, creep is controlled by bow-out and climb of dislocation segments pinned at lath boun daries and second-phase particle. Analysis of the dislocation substructure is presented to give some support for this mechanism. (C) 2001 Elsevier Sci ence Inc. All rights reserved.