Four Dimensional (4D) X-ray Microtomography of Stress-Corrosion Cracking in High Performance Metallic Materials
Abstract
The stress corrosion cracking and of aluminum alloys is very important in structural applications. State-of-art in situ x-ray tomography techniques for microstructural characterization are ideal for providing a fundamental quantitative understanding of microscopic mechanisms of damage evolution over time. The insight provided by these techniques will result in unprecedented advances in our understanding of the physics of combined stress and environmental effects on plasticity and mechanisms for degradation and damage evolution. Specifically, the following important issues need to be addressed: 1. The physics of plastic zone formation and evolution as a function of environment, in 3D, needs to be investigated. Specifically, how do the combined effects of diffusion, galvanic corrosion, and microstructure affect local crack tip plasticity? The effect of crystallography of grains needs to be investigated. Measurement of the magnitude of the plastic zone size in NaCl solution versus monotonic plastic zone size in air, needs to be conducted. 2. Stress corrosion cracking. Microstructural effects are taking place during SCC. It is not clear which is most important, or whether there is any synergy between these mechanisms. The use of in situ tomography can be used to visualize the mechanisms, as well as obtain quantitative information, such as the evolution of hydrogen from the crack surfaces. Combined with correlative tomography techniques, such as combining XCT and focused ion beam tomography, we can extend the length scales to that of the crystallography of the grains and the precipitate structure. 3. Corrosion-Fatigue crack growth at specific crystallographic boundaries. Using Diffraction contrast tomography (DCT) to determine, non-destructively, the orientation of the grains, and the type of grain boundaries, we can introduce sharp cracks using the FIB and conduct systematic studies of the effect of boundaries on corrosion-fatigue behavior. Here we propose to use 4D x-ray synchrotron tomography to quantify in situ stress corrosion cracking and obtain a physical basis for SCC in a corrosive environment. This work will be conducted on a 7000 series Al alloys. Image segmentation and 3D reconstruction will be used to quantify in situ crack growth, as well as the volume fraction of hydrogen bubbles formed dynamically during the corrosion process. DCT will be used to obtain 3D crystallographic information about the grains and its effect of SCC and crack growth during corrosion-fatigue. The synergistic effects of inclusions and grain orientations/boundaries on nucleation of corrosion pits as well as the crack growth processes will be obtained through this work.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 27, 2018
- Source ID
- N000141812554
Entities
People
- Nikhilesh Chawla
Organizations
- Arizona State University
- Office of Naval Research
- United States Navy