Environmentally Assisted Cracking: Theory and Practice: Corrosion and Degradation in Harsh Environments
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
Thursday 8:30 AM
March 23, 2023
Room: Aqua 314
Location: Hilton
Session Chair: Ramprashad Prabhakaran, Pacific Northwest National Laboratory; Mohsen Dadfarnia, Seattle University
8:30 AM Invited
A Comprehensive Study to Evaluate Sensitization of As-fabricated Coated TPBAR Cladding: Ramprashad Prabhakaran1; Venkateshkumar Prabhakaran1; Dan Edwards1; David Senor1; Andy Casella1; 1Pacific Northwest National Laboratory
A comprehensive sensitization study was performed to evaluate as-fabricated coated tritium-producing burnable absorber rod (TPBAR) cladding that has higher potential for sensitization due to the aluminide coating process by utilizing various techniques, such as optical metallography, SEM, electrolytic etching, electrochemical potentiokinetic reactivation (EPR) and scanning electrochemical cell microscopy (SECCM). SEM showed that coated specimens have a significant number of carbides on grain boundaries indicating a degree of sensitization. Metallographic etching revealed step and ditched microstructures in uncoated and coated samples, respectively. The effect was higher near the inner surface (coating side). EPR single loop and double loop tests showed that the corrosion current and normalized charge of coated specimens is about three orders of magnitude higher than that of uncoated specimens. SECCM showed that the corrosion current close to the inner surface is much higher. This correlated well with the microstructure of coated specimens after the EPR double loop test.
9:00 AM
Utilizing Predictions from Precipitation Modeling to Produce 5XXX Series Aluminum Alloy Plate with Lowered Sensitization Responses: Matthew Steiner1; Likun Sun1; 1University of Cincinnati
As super-saturated solid solutions of Al-Mg, 5XXX series aluminum alloys are susceptible to sensitization via intergranular precipitation of the anodic β-phase, which promotes intergranular corrosion, exfoliation and stress corrosion cracking in marine environments. Building upon an improved understanding of how grain boundary β-phase precipitates impact the sensitization response, which closely follows a Johnson-Mehl-Avarami-Kolmogorov (JMAK) model adapted to handle the impinging locally sensitized regions surrounding discrete β-phase precipitates, a clear change in the β-phase nucleation and growth kinetics in these alloys can be observed above 100°C. Taking advantage of predictions based upon this model, we will demonstrate that it is possible to reduce the sensitization kinetics in these alloys to nearly half their original rate in the as-received plate condition through a novel and minimally invasive pre-treatment strategy, doubling the possible service lifetime of these alloys.
9:20 AM
Preventing the Sensitization in Aluminum Magnesium Alloys: Ramasis Goswami1; 1Naval Research Laboratory
Al 5000 series alloys are widely used for boat and ship structural applications. However, it becomes susceptible to intergranular corrosion and stress corrosion cracking (SCC), as a result of the formation of the grain boundary beta phase, Al3Mg2, which is anodic relative to the Al matrix. The SCC susceptibility occurs as a result of thermal exposure in the range of 50-200C. This leads to a catastrophic structural failure via anodic dissolution of the grain boundary phase upon exposure to seawater. We demonstrate here the beta phase formation in aluminum-magnesium alloys has been suppressed by alloying with small amount of boron. TEM and XRD observations revealed that a boride compound, AlMgB2, forms at grain boundaries and within aluminum matrix, and the beta phase does not nucleate and grow at grain boundaries upon extended annealing. This is a significant finding as it addresses the longstanding problem of sensitization in aluminum-magnesium alloys.
9:40 AM
Localized Corrosion Behavior of Aged High Zinc 7068 Aluminium Alloy: Ankur Kumar1; G P Chaudhari1; S K Nath1; 1IIT Roorkee
It is reported that over-ageing is less effective in developing SCC-resistant high-zinc 7xxx series aluminum alloys. Therefore, SCC performance of > 7 wt% zinc containing 7068 alloy needs to be evaluated in different ageing conditions. Microstructures after different ageing treatments are correlated with mechanical properties, intergranular corrosion (IGC) and SCC susceptibility. Dissolution of second phase precipitates occurred from selective leaching of magnesium and aluminum. Besides overaged alloy, the peak aged alloy also exhibited higher resistance to IGC and SCC.
10:00 AM Break
10:20 AM Invited
Mechanistic Model for Hydrogen Accelerated Fatigue Crack Growth in a Low Carbon Steel: Mohsen Dadfarnia1; Zahra Hosseini2; Masanobu Kubota3; Akihide Nagao3; Brian Somerday2; Petros Sofronis2; Robert Ritchie4; 1Kyushu University; Seattle University; 2Kyushu University; University of Illinois at Urbana-Champaign; 3I2CNER, Kyushu University; 4University of California, Berkeley
Fatigue crack growth in the presence of hydrogen is a severe mode of environmental failure. Although this failure mode has been the subject of intense investigation over several decades, a mechanistic model is still lacking. In this study, we present a model for fatigue crack propagation induced by alternating crack tip plastic blunting and re-sharpening and in which crack growth is governed solely by the plastic dissipation ahead of the propagating crack. The Chaboche constitutive model is used for the calculation of the stress and strain fields. The model is calibrated using a sequence of experimental data from uniaxial strain-controlled cyclic loading tests and uniaxial stress-controlled ratcheting tests of a low carbon steel, JIS SM490YB, in the absence and presence of hydrogen. The numerical simulation results indicate that the proposed crack propagation model can predict Paris law behavior in the absence and presence of hydrogen.
10:50 AM
Influence of Pre-Deformation on High Temperature Oxidation of a Model Fe-Cr-Ni Alloy in Pressurized Water Reactor Environments: Dallin Barton1; Tingkun Liu1; Cheng-Han Li1; Matthew Olszta1; Ziqing Zhai1; Ferdinan Colin1; Mychailo Toloczko1; 1Pacific Northwest National Laboratory
Stress corrosion cracking (SCC) is a potential degradation mode for stainless steels (SS) in pressurized water reactors (PWR), especially in components with unexpected imposition of excessive cold work. While several mechanisms have been proposed over the decades to explain SCC of SS in PWR primary water environments, crucial voids remain in experimental verification of any unified SCC theory. Part of this includes a lack of understanding of the influence of applied stress on modifying the oxidation behavior of SS in PWR-type coolants. We present a systematic study on the influence of prior applied deformation on the structure and composition of oxides formed on a model Fe-18Cr-14Ni alloy after being exposed to PWR primary water under tensile stress. Several nano-scale characterization tools elucidates the influence of deformation-induced microstructure on oxidation mechanisms. Specifically, we will discuss how deformation-induced defects enhances the outward cation diffusion, leading to larger oxide phase formation.
11:10 AM
Effect of Mo and W on Corrosion of Ni-superalloys: Cynthia Rodenkirchen1; 1Imperial College London
Hot corrosion of Ni-based superalloys for aeroengine applications is commonly observed at temperatures around 900 °C (type I) and 700 °C (type II). Recently, a new type of hot corrosion including environmentally assisted cracking has been observed at unexpectedly low temperatures around 550 °C. This work investigates the effect of alloying elements Mo and W on corrosion resistance of Ni-based superalloys at 550 °C through characterisation of developmental alloys with systematic compositional changes. Oxide scale formation as the first barrier against hot corrosion and surface corrosion under salt and SO3(g) environment at 550°C are compared to oxidation and corrosion at 700 °C. Environmentally assisted cracking under salt, SO3(g), and fatigue load at 550°C is compared to cracking in vacuum and air, providing insights into the mechanisms of this new type of corrosion, the role of a corrosive environment and the effect of Mo and W additions, informing future alloy developments.