Correlating Microstructure to Corrosion Susceptibility using a Multiscale Electron Microscopy Approach
Abstract
Naval operations are conducted almost exclusively in aggressive environments, necessitating the inclusion of corrosion-mitigation in" every design process and costing the armed forces billions of dollars annually in prevention and maintenance. One prominent exampl"e of this is the performance of Al alloys used as structural components in air and watercraft, which are desirable for their high st"rength-to-weight ratio but are susceptible to the development of corrosion pits in chlorine environments such as sea water. While r"elatively minor in terms of volume of material affected, these corrosion pits can act as critical flaws for fatigue crack nucleation" and lead to catastrophic failure under applied loads. Improving the intrinsic corrosion resistance of Al alloys without adversely affecting mechanical properties would increase the safety and reliability of these alloys in deployment. One potential approach to" corrosion-resistant material design is through processing-based microstructure manipulation, but to pursue this approach requires a" fundamental understanding of the relationship between microstructure and corrosion susceptibility. Past studies have shown that c"orrosion rates can vary considerably with microstructure, accounting for example, for the increased corrosion resistance of some nan""ograined alloys. However, these studies have largely focused on isolating a single aspect of the microstructure such as the grain si"ze or chemical distribution to explain the observed behavior. These attempts at one-to-one correlations can often be misleading as any processing routine will invariably affect multiple aspects of the microstructure. My hypothesis is that multiple aspects of the" microstructure interact synergistically to influence local and global corrosion rates. To explore this hypothesis, I will explore p""itting corrosion of Al alloys in chlorine environments using a two-pronged approach, 1) using novel in situ TEM corrosion experiment"s to resolve the mechanisms associated with corrosion at the nanoscale and 2) using a data science-driven approach combining correlation functions with high-resolution electron backscatter analysis to simultaneously account for multiple aspects of the microstructu"re, including orientation, grain size distribution, grain shape, grain boundary character distribution, chemical heterogeneities, di""slocation density, and residual strain gradients, and their effect on corrosion rates. These data will be correlated with post-corro"sion characterization using surface profilometry to identify local corrosion rates as well as average corrosion pit size and density.The expected output of this research will be a phenomenological relationship linking microstructure to corrosion mechanisms and ra"tes, specific to Al in chlorine environments but expected to be widely informative for a range of material/environment combinations." The value of this research and its impact on DoD capabilities is in understanding how susceptibility to corrosion rate varies with local conditions (e.g. near weld sites or in mechanically deformed parts) and as a guide towards developing increasingly corrosion resistant materials.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 07, 2017
- Source ID
- N000141712646
Entities
People
- Josh Kacher
Organizations
- Georgia Tech Research Corporation
- Office of Naval Research
- United States Navy