High-Temperature Creep and Threshold Stress of Precipitation-Hardened Al-0.7 at%Mn Alloy

In order to examine the validity of Srolovitz’s attractive interaction theory in dispersion-hardened alloys, high-temperature creep behavior of Al-0.7 at%Mn alloy has been studied in a wide stress range covering both sides of the calculated Orowan stress. It has been found that there is a clear threshold stress for creep deformation at the highest test temperature of 723 K. The stress is approximately equal to the stress estimated from the attractive-interaction hardening, σ_v, which is nearly equal to the Orowan stress in this alloy. TEM observation also suggests that the interaction between dislocations and Al₆Mn particles is of attractive type. Further, it has been shown that the threshold stresses reported so far in dispersion-hardened alloys are well explained by the attractive interaction. Stress dependence of steady-state creep rate is very different between the high and low stress regions, the stress exponent, n, being 14–21 and 4, respectively. The stress dependence of n is commonly observed in dispersion-hardened alloys. Their boundary stress increases with decreasing temperature, and the activation energy for creep deformation, Q_c, in the high stress region is much higher than that for self-diffusion in pure Al, while the value of Q_c in the low stress region is nearly equal to the activation energy for pipe diffusion. These values of n and Q_c are discussed on the basis of available theories.