Comparison of the Microstructure, Tensile, and Creep Behavior for Ti-24Al-17Nb-0.66Mo (Atomic Percent) and Ti-24Al-17Nb-2.3Mo (Atomic Percent) Alloys

摘要

The effect of small molybdenum additions, 0.66 and 2.3 at. pct, on the microstructure, tensile, and creep behavior of a nominally Ti-24Al-17Nb (at. pct) alloy was investigated. The alloy containing 2.3 at. pct Mo contained higher body-centered-cubic (bcc) phase volume fractions, which was expected as Mo stabilizes the bcc phase. Constant load, tensile-creep experiments were performed in the stress range of 29 to 275 MPa and the temperature range of 650 deg C to 710 deg C, in both air and vacuum environments. In-situ creep experiments were performed inside a scanning electron microscope chamber in order to identify the deformation evolution from surface observations. From these experiments, it was evident that alpha_2 intergranular cracking was prevalent and initiated the fracture process where the crack path followed the alpha_2 grain boundaries. The Ti-24Al-17Nb-2.3Mo (at. pct) alloy exhibited significantly lower creep rates than the Ti-24Al-17Nb-0.66Mo (at. pct) alloy, and this was associated with less contiguity of the alpha_2 phase.