Effect of nano-scale particles on the creep behavior of 2014 Al

The creep behavior of two grades of 2014 Al was investigated over six orders of magnitude of strain rate. While these two grades were prepared by powder metallurgy (PM), they have different oxygen levels (0.3 and 1.0 wt.% oxygen). The creep data show that the creep behavior of these two grades of PM 2014 Al is similar to that of dispersion strengthened (DS) alloys with regard to the following characteristics: (a) the apparent stress exponent is high and variable, and (b) the apparent activation energy is higher than that for self-diffusion in Al. An analysis of the experimental data indicates that there exists a threshold stress for creep whose temperature dependence is strong. The values of threshold stress increase noticeably with the increase of oxygen content in the alloy. This finding together with the observation of extensive interaction between moving dislocations and nano-scale dispersion particles indicates that the presence of oxide particles is responsible for the threshold stress creep behavior in 2014 Al. By considering the effect of the threshold stress, it is demonstrated that the true creep characteristics of PM 2014 Al are consistent with those reported for Al solid-solution alloys.