The formation of creep cavities at high temperatures is a critical factor limiting the formability of light alloys. Cavity nucleation is typically associated with stress concentrations at second phase particles, substructures, grain boundaries, and triple junctions. Cavity growth is attributed to diffusion, plasticity, or superplasticity. While extensive theoretical studies have explored cavity growth, experimental investigations of nucleation and early growth stages remain limited.
Methods
Researchers at the European Synchrotron, led by Dr. Kumar, employed in situ nanotomography, combining synchrotron X-rays with 100 nm pixel size and 7 s scan time, to observe and analyze cavity nucleation and growth in Al-3.6 wt% Cu alloy during high-temperature creep deformation (7.9 MPa, 698 K). This approach aimed to provide insights into the micro-mechanisms governing cavity nucleation and growth.
Real-time observation of creep cavities in Al-Cu alloy was achieved for the first time using in situ nanotomography. The influence of pre-existing porosity on cavity nucleation and growth was revealed. The study elucidated the evolution of cavity growth mechanisms with increasing strain.
This research, through in situ nanotomography observation of creep cavity evolution, offers new insights into the mechanisms of cavity nucleation and growth during high-temperature creep.
Fig. 1. (a) Top view (XY) and (b) side view (YZ) 2D slices from the low-resolution volume of the Al-Cu sample at the start of deformation; second phase particles are indicated in black and are seen to line up along the grain boundary. Also, the region of interest is indicated, which is probed in the high-resolution scans. The position of the two slices with respect to each other are indicated by the blue line. (c) High-resolution 3D rendering of the Al-Cu sample at the start of deformation, with second phase particles (green) and pre-existing cavities (red).
Fig. 2. 3D rendered view of growth of cavity (red) alongside a second phase particle (green) as the Al-Cu sample strains (Ɛ) with time (t, in minutes).
Fig. 3. (a) Plot showing change in transition radius obtained from model with time of sample deformation. (b) Transition radius obtained experimentally vs transition radius from model, for Al-Cu sample. The red line is a straight line with a slope of 1. The transition radius refers to the cavity radius at which the cavity growth mechanism transitions from a diffusion-controlled mechanism to a plasticity-controlled mechanism.
Authors
The first and corresponding author of this work is Dr. Richi Kumar from the European Synchrotron.
Editor's comment:
Creep cavity evolution is a key factor in the premature failure of high-temperature alloys. In-situ nano-tomography allows for real-time, 3D observation of this process, aiding in understanding the mechanism and improving predictive models. This technology is underutilized, and further research is needed to advance the field.
