Cyclic Stress-Strain Response and Damage Mechanisms at High Temperature

Publisher Website
Google Scholar
Abstract
The cyclic stress-strain response and damage of commercially pure nickel, thoria dispersed (TD) nickel, and Al-4Cu alloy aged to contain θ′ and θ″ are investigated as a function of test temperature. Up to 23 melting point, the slipband morphology, and hence the crack nucleation mechanism, does not change in nickel and TD-nickel when tested under vacuum using a symmetrical sawtooth waveform. The microstructure containing θ′, however, exhibits an increased tendency toward transgranular slip with increase in temperature. This is quite contrary to our intuition and is shown to be due to the plastic deformation of the θ′ precipitate and subsequent dissolution at high temperatures. The θ″ microstructure exhibits intense slipband deformation and cracking at all tested temperatures; this is surprising in view of the metastability of the microstructure and the fact that cyclic disordering of the crystal structure could be reordered at high temperatures. Both of these factors would be expected to homogenize the slip, but this was not observed.