Connecting AM Processing Variables to Microstructure to Corrosion Behavior
Abstract
There is a lack of quantitative mechanistic understanding of the connections between corrosion performance and additive manufacturing processing parameters, initial particle characteristics, and resultant microstructures. Key, unresolved issues include what microstructural features in AM materials control the environmental degradation behavior in Navy-relevant environments, to what extent can existing knowledge of wrought materials systems be used to understand/interpret these AM materials in terms of the microstructural features that corrosion environmental degradation, what effects do varying AM processing parameters have on the development of the microstructure features that govern the corrosion, hydrogen behavior, and environmental cracking behavior, and to what extent must standardized corrosion testing be modified to account for the different microstructures developed in AM materials vs. the legacy produced alloys for which the tests have been optimized. The first step of the proposed work will be to select an alloy system of high interest to applications that has both a legacy processing path and a standardized AM processing path to allow comparisons to be made. The selected alloy systems will have been extensively characterized for material that has been conventionally manufactured, and each will have its own set of corrosion susceptibilities. Extensive comparative microstructural characterization would be performed across the mm to nm length scale. The goal of this aspect of the work would be identification of potential microstructural culprits based on chemistry, microstructural location, geometry. Optical, scanning electron, and transmission electron microscopies would be used to develop a comprehensive understanding of the alloy selected and the impact of AM processing vs. legacy processing on the microstructure. Appropriate standardized corrosion and mechanical testing for the alloy on both legacy-processed material and AM-processed material will be performed to both identify and quantify any differences in behavior and to connect to testing approaches already embedded in the USN protocols for material selection. The specific corrosion and EAC testing will be selected based on the type of corrosion for which that alloy class has shown susceptibility and the relevant expected operation environments. These data will also help connect the specialized scientific studies described below to Navy-relevant testing approaches. The same methods for assessing the microstructure before testing will be used to identify the critical microstructural features exposed during the testing. State-of-the-art measurements will be used to understand the reasons for differences in corrosion behavior between the legacy-processed material and AM-processed material based on the microstructural features identified. Electrochemical testing will probe differences in corrosion rate, susceptibility to localized corrosion (including dealloying). Thermal desorption spectroscopy and advanced hydrogen permeation methods will be used to quantitatively understand the impacts of the processing differences on the impact of absorbed hydrogen on the cracking behavior. High-resolution fracture mechanics-based methods will be used to clarify the impact of the differences in microstructure on both stress-corrosion cracking and corrosion-fatigue behavior. The measurements described above will be used to develop a mechanistic description of the role of the culprit microstructural features in controlling the corrosion resistance of the AM material. The hypotheses defining that description will be tested using AM samples purposely manufactured in ways that will exacerbate or minimize the presence or potency of the microstructural features of importance.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 12, 2023
- Source ID
- N000142312381
Entities
People
- Robert M. Kelly
Organizations
- Office of Naval Research
- United States Navy
- University of Virginia