Environmentally Assisted Cracking: Theory and Practice: Stress Corrosion Cracking II
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Bai Cui, University of Nebraska Lincoln; Raul Rebak, GE Global Research; Srujan Rokkam, Advanced Cooling Technologies, Inc.; Jenifer Locke, Ohio State University
Wednesday 2:00 PM
March 22, 2023
Room: Sapphire 410B
Location: Hilton
Session Chair: Janelle Wharry, Purdue University; James Burns, University of Virginia
2:00 PM Invited
CISCC Repair & Mitigation Strategies in Nuclear Waste Storage Canisters: Janelle Wharry1; Antonio Ramirez2; Frank Pfefferkorn3; Kumar Sridharan3; Indrajit Charit4; Vijay Vasudevan5; Luke Brewer6; Paul Allison6; Jonathan Tatman7; 1Purdue University; 2The Ohio State University; 3University of Wisconsin; 4University of Idaho; 5University of North Texas; 6University of Alabama; 7Electric Power Research Institute
This talk captures the state-of-the-research of repair and mitigation of chloride-induced stress corrosion cracking (CISCC) in nuclear waste storage canisters. In the U.S., more than 86,000 metric tons of nuclear waste are stored in stainless steel canisters within concrete overpacks. But the CISCC susceptibility of canister vertical seam welds is a mounting concern in the nuclear industry. Herein we evaluate solid-state technologies for repair and mitigation of canister CISCC, including cold spray, friction stir joining/surfacing, and friction stir additive (MELD) manufacturing. These technologies have been evaluated in accelerated chloride environments (e.g., Fe3Cl, MgCl2) and in less aggressive saltwater brine. All technologies show promise for reducing pitting, increasing crack initiation time, and repairing existing CISCC. However, CISCC suppression mechanisms may lead to CISCC susceptibility elsewhere on the canister. The state of knowledge will be discussed in the context of the practical implications of deploying CISCC repair and mitigation technologies.
2:30 PM
Phase Field Modelling of Stress Corrosion Cracking in Superalloys at High Temperature: Mustafa Elsherkisi1; Fabian Duarte Martinez1; Simon Gray1; Gustavo Castelluccio1; 1Cranfield University
The reliability of turbine engines strongly depends on the environment through which aircrafts fly. Humidity, contaminants, operating stresses, and temperatures determine the likelihood of cracking. Simultaneous crack initiation at multiple locations lead to crack interaction, either in the form of shielding or coalescence, which has the potential for arresting damage or accelerating catastrophic failures. This presentation will introduce a novel approach using Phase Field models to evaluate crack propagation and crack interaction in CMSX-4 C-Ring tests. The model assumes that contaminants diffuse and reduce the material critical energy release rate, which enables crack propagation. The model, which is calibrated to enable cracking above a threshold stress, predicts the crack spacing that results in shielding or coalescence. Simulations led to novel experiments designed to prove shielding effects.
2:50 PM
Susceptibility of Manganese Bronze to SCC in Water: Olaf Manz1; Milo Kral1; 1University of Canterbury
C86300 manganese bronze (~25wt.%Zn, 3.0-7.5Al, 2.5-5.0Mn, 2.0-4.0Fe, rem. Cu) is a high strength beta brass alloy typically centrifugal or continuous cast, often for bearing applications. This alloy has recently been found to be susceptible to stress corrosion cracking (SCC) when exposed to moisture from the atmosphere and residual stresses from manufacturing. There are only a few documented cases in the literature of this and other copper-based alloys experiencing SCC by exposure to water. The present research aims to determine relationships between the SCC susceptibility in water and other aqueous environments by varying stress and small alloying additions. ‘C-ring’ samples were manufactured from C86300 and variants, following ASTM G38, then tested for SCC at varying applied stresses in de-ionized water. Optical and electron microscopy were used to perform microstructural analysis of samples to both verify the fracture mechanism and relate the observed microstructures to the collected data.
3:10 PM Cancelled
Stress Corrosion Mitigation in Al-Mg via Zn-Rich Primers in Atmospheric Environment: Matthew McMahon1; Eric Dau1; Allison Akman1; 1Naval Surface Warfare Center, Carderock Division
The Al-Mg alloy AA5456 achieves a unique combination of weldability, general marine corrosion resistance, and high strength-to-weight ratio when utilized at relatively low temperatures in service. However, prolonged exposure to temperatures of at least 40ᵒC promotes Mg diffusion to the grain boundaries to form the highly anodic β phase in a process termed sensitization, which promotes stress corrosion cracking (SCC) and premature failure in seawater conditions. Previous work demonstrated that inorganic Zn-rich primers have a unique capability to mitigate β phase corrosion and, thus, SCC in full immersion marine conditions. This work will evaluate the efficacy of these primers to achieve SCC mitigation in atmospheric conditions in both the as-received and depleted conditions to understand their limits and to identify top performers for potential in-service use on highly sensitized AA5456. Testing will consider primers in the defected state with complex salt spray procedures for additional simulated environmental severity.
3:30 PM Break
3:50 PM Invited
On the Applied Potential Dependence of Environment-assisted Cracking Behavior of 7xxx-series Al Alloys in Marine Environments: Towards Informing Metal-rich Primer-based Mitigation Strategies: James Burns1; Zach Harris1; Alen Korjenic1; John Scully1; 1University of Virginia
Metal-rich primers (MRPs) have been shown to effectively attenuate the environment-assisted cracking (EAC) susceptibility of 5xxx-series Al alloys exposed to marine environments, suggesting that such galvanic protection schemes may be suitable for use on 7xxx-series Al alloys. A detailed understanding of the relationship between EAC susceptibility and the applied electrochemical potential is needed to design effective MRPs, but such relationships are not well-understood in 7xxx-series Al alloys. Fracture mechanics experiments were performed on AA7075-T651 and AA7050-T7451 in 0.6 M NaCl at applied potentials ranging from -1300 to -750 mVSCE (vs. saturated calomel electrode) and fixed loading rates (dK/dt) ranging from 0 to 2.0 MPa√m/hr. A small potential ‘window’ of reduced susceptibility is observed in AA7075, but crack growth kinetics remain sufficiently severe that MRPs are unlikely to prevent EAC. Conversely, AA7050 exhibits a potential ‘window’ with sufficiently suppressed crack growth kinetics that MRPs could potentially be used to mitigate EAC.
4:20 PM
Understanding the Effect of Applied Potential on Stress Corrosion Cracking of AA6111 Through In-Situ Measurements of Crack Tip pH: Katrina Catledge1; Jenifer Locke1; 1Ohio State University
While AA6xxx Al-Mg-Si alloys are typically regarded as resistant to stress corrosion cracking (SCC), particularly when compared to other age-hardenable Al alloys, research shows that anodic polarization results in a significant decrease in SCC resistance. Specifically, slow strain rate testing under full immersion in 0.6M NaCl solution show that the threshold for stress corrosion cracking (KTH) decreases ~18 MPa√m to below 6 MPa√m when polarized 100 mV above the freely corroding potential. Early results show that the crack tip pH when the stress intensity (K) is above KTH is acidic. Research is currently underway to utilize micro-pH electrodes to probe the crack tip pH when the crack is actively growing and transitioning into arrest or vice versa as either K or the applied potential is altered. The findings from this research will inform on the risk of galvanic coupling in automotive applications to induce SCC in automotive Al alloys.
4:40 PM
Understanding Sensitization Rate Effects on Stress Corrosion Cracking for 5xxx Marine Grade Aluminum Alloys: William Golumbfskie1; Emily Holcombe1; Eric Dau1; Matthew McMahon1; 1Naval Surface Warfare Center-Carderock Division
5xxx aluminum alloys are used in marine applications due to their corrosion resistance coupled with high as-welded strength. A current concern is that 5xxx alloys can become sensitized in service, ultimately leading to stress corrosion cracking (SCC). Sensitization occurs when magnesium precipitates out of solution forming a deleterious beta-phase (Mg2Al3) continuously around grain boundaries. The extent and rate of sensitization is dictated by exposure to elevated temperatures.This study will evaluate the SCC performance of 5083 and 5456 alloys with respect to degree of sensitization and sensitization rate. Slow rising stress intensity testing is used to quantify the effects of sensitization on IG-SCC susceptibility, identifying differences in threshold stress intensity in potentiostatic conditions and full seawater immersion. Microscopy coupled with Electron backscatter diffraction (EBSD) will be used to characterize the material microstructure, to link the extent and location of beta-phase formation to resultant SCC performance.
5:00 PM
Effect of Microstructure on Stress Corrosion Cracking Behavior of Additively Manufactured 7050-based Aluminum Alloy: Rupesh Rajendran1; Crosby Owens2; Jeffrey Eisenhaure2; David Spain2; Alex Kinsey2; Preet Singh1; 1Georgia Institute of Technology; 2Northrop Grumman Corporation
Aluminum alloy 7050 is well known candidate for aerospace applications due to its high strength to weight ratio, corrosion and stress corrosion cracking (SCC) resistance, and fracture toughness properties. However, there has been limited studies on understanding the SCC behavior of additively manufactured (AM) high strength aluminum alloys. This work investigates the SCC behavior of AM 7050-based aluminum alloys which were modified to promote equiaxed grain structures with minimal manufacturing-related defects. SCC behavior is studied using slow strain rate tests (SSRT) under dry air, NaCl, and oxidizing environments. The effect of microstructural differences on the SCC behavior as a result of different post-processing and aging conditions are also explored. Results show high SCC resistance of AM 7050-based alloys in general, compared with an equivalent wrought alloy. Post-SCC samples are characterized using SEM-EDS, EBSD, and fractography to correlate microstructural features responsible for higher SCC resistance in AM 7050-based aluminum alloy.