Effect of stress-temperature regimes on creep mechanisms in Ti-24Al-11Nb

The steady state creep rate (SSCR) of various microstructures of Ti-24Al-11Nb (a/o) has been determined. SSCR vs. stress and vs. temperature curves were determined to find Qa, apparent creep activation energy, and to investigate n, power law stress exponent. At low stresses, apparent creep activation energies determined for all microstructures were found to be between 106 kJ mol−1 and 156 kJ mol−1, which agrees fairly well with the energy for self-diffusion in alpha titanium, and the energy of interdiffusion on the Al-rich side of the α2 phase in Ti3Al, both having a value of 150 kJ mol−1. In many SSCR vs. stress curves, a slope change was observed in the stress range investigated. As temperature increased, slopes decreased towards unity, suggesting that different creep mechanisms, i.e. dislocation creep and diffusional creep, may be rate-controlling in different stress-temperature regimes.