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

Abstract

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, σv, 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, Qc, in the high stress region is much higher than that for self-diffusion in pure Al, while the value of Qc in the low stress region is nearly equal to the activation energy for pipe diffusion. These values of n and Qc are discussed on the basis of available theories.