Environmentally Assisted Cracking: Theory and Practice: Stress Corrosion Cracking I
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
Tuesday 8:30 AM
February 25, 2020
Room: Theater A-10
Location: San Diego Convention Ctr
Session Chair: Gary Was, University of Michigan; John Scully, University of Virginia
8:30 AM Invited
Insights into Factors Controlling IASCC of Stainless Steels: Gary Was1; Drew Johnson1; Diana Farkas2; 1University of Michigan; 2Virginia Tech
Irradiated stainless steels are susceptible to degradation in high temperature water by the process of irradiation assisted stress corrosion cracking (IASCC). While a general understanding of the process is emerging, there are several interesting observations that have yet to be incorporated into a complete description of the mechanism. It is now known that the local stress at the grain boundaries at sites of dislocation channel impingement plays a critical role, as does the composition of the surface oxide over the grain boundary. Other factors such as the presence of second phases near grain boundaries and the overall composition of the steel can significantly affect the cracking susceptibility. Still, the low percentage of cracked boundaries suggests additional factors. Incorporation of factors besides stress and oxide composition into the overall mechanism of IASCC will be the subject of this talk.
9:10 AM
Effect of Triaxial Stress State on PWSCC Initiation Behavior of Nickel-based Alloy in Nuclear Power Plants: Seung Chang Yoo1; Kyoung Joon Choi2; Jong-Sung Kim3; Il Soon Hwang1; Ji Hyun Kim1; 1UNIST; 2Korea Atomic Energy Research Institute; 3Sejong University
Effect of triaxial stress on the PWSCC initiation of nickel-based alloy was investigated. Thermal aging was simulated by heat treatment at 400 °C which does not cause an excessive formation of second phases that cannot be formed in nuclear power plant service conditions. Triaxial stress was applied by making round notch at reduced section of tensile test specimens. Detail microstructural analysis was conducted with electron microscopy, electron back-scatter diffraction, etc. Slow strain rate test with direct current potential drop method was conducted to evaluate stress corrosion crack initiation susceptibility in primary water environment. PWSCC initiation time of 10 y thermally aged specimen was the shortest while those of as-received and 20 y thermally aged specimen was longer than that. However, the trend was changed under triaxial stress state; 20 y thermally aged specimen marked the highest susceptibility to PWSCC initiation while as-received specimen showed the lowest susceptibility.
9:30 AM
Determining Reliability Over Time for Stainless Steels Susceptible to Chloride-induced Stress Corrosion Cracking: Consuelo Guzman-Leong1; Joseph Cluever1; Stephen Gosselin1; 1LPI, Inc.
Failure of corrosion-resistant materials due to chloride-induced stress corrosion cracking continues to threaten long-term plant operations and component integrity. A probabilistic model was developed to address degradation of austenitic stainless steel components from chloride-induced SCC in order to help plant owners make guided run, repair, replace, and inspect decisions. Consistent with observations in the literature, the SCC probabilistic model assumes the presence of stress, a corrosive environment, and susceptible material, and further assumes that pitting corrosion is a precursor to SCC. Calculation of the probability of exceeding a wear allowance and through-wall penetration from SCC are performed by calculating the formation and progression to a stable pit, the conditional probability that SCC becomes dominant over pitting, and the crack growth rate as a function of the crack tip stress intensity factor. This paper illustrates the probabilistic model’s sensitivity to key stressors of chloride-induced SCC.
9:50 AM Break
10:10 AM Invited
Mitigation of Intergranular Stress Corrosion Cracking in Al-Mg Alloys Through the Electrochemical and Chemical Effects of Metal Rich Primer Coatings Near Stationary and Propagating Cracks: Matthew McMahon1; John Scully1; James Burns1; 1University of Virginia
This talk will demonstrate galvanic and chemical protection phenomena achieved by metal-rich primer coatings on, as well as new mechanistic understanding of stress corrosion cracking in Al-Mg alloys. Mildly elevated temperatures can lead to intergranular precipitation of the β phase (Al3Mg2) in Al-Mg alloys. The β phase is highly anodic to the matrix and in the presence of corrosive environments can lead to intergranular stress corrosion cracking [4]. This behavior is governed by a coupled anodic dissolution process (of the β phase and under certain conditions the Al matrix), which by the hydrolytic acidification mechanism catalyzes an aggressive local crack tip chemistry. In order to systematically discuss the mitigation and newfound insights into this mechanism, four main topics will be sequentially covered concerning stationary as well as propagating cracks: (1) mild cathodic polarization via potentiostat, (2) galvanic effects of metal-rich primer coatings, and (3) chemical protection effects provided by Zn2+.
10:50 AM
Sensitization, Loading Frequency, and Electrochemical Potential Effects on Corrosion Fatigue Kinetics of AA5456-H116: David Schrock1; Jenifer (Warner) Locke1; 1The Ohio State University
5xxx series aluminum-magnesium alloys possess excellent corrosion resistance in the as-fabricated condition. However, alloys with greater than 3 wt.% Mg can become sensitized after sufficient exposure above 40 °C. Sensitization increases susceptibility to environment assisted cracking. In this work, effects of sensitization level (DoS), fatigue loading frequency (f), and electrochemical potential on AA5456-H116 corrosion fatigue kinetics (da/dN) in 3.5 wt.% NaCl are investigated. Results reveal an inverse relationship between da/dN and loading f in microstructures with DoS of 24 mg/cm2 or greater. At a singular low f (0.03 Hz), high DoS (65 mg/cm2) accelerates da/dN fivefold over microstructure in the as-fabricated condition. Microstructures having DoS of 22 mg/cm2 or less are unaffected by sensitization and have f-independent da/dN below 1 Hz. Cathodic polarization to −970 mVSCE, below β breakdown, reduces da/dN an order of magnitude below da/dN at OCP. Hypotheses regarding the source of the inverse f-dependence will be discussed.
11:10 AM
Evaluating Stress Corrosion Cracking Performance of 5083 H116 Aluminum as a Function of Material Microstructure: William Golumbfskie1; Matthew McMahon1; Emily Holcombe1; Mitra Taheri2; 1Naval Surface Warfare Center - Carderock; 2Drexel University
5xxx aluminum alloys are commonly used in marine applications due to their corrosion resistance coupled with high as-welded strength. A potential concern is that 5xxx alloys can become sensitized in service, which could lead to stress corrosion cracking (SCC). Sensitization occurs when magnesium precipitates out of solution forming a deleterious beta-phase (Mg2Al3) continuously around grain boundaries. Prior work has shown a variation in sensitization rate as a function of processing and resultant material microstructure. This study will attempt to quantify the extent of SCC as a function of sensitization rate for 5083 H116 plate having varied processing parameters. Slow rising stress intensity testing will quantify the effect of sensitization and percent recrystallization on IG-SCC susceptibility through identifying differences in threshold stress intensity in potentiostatic conditions and full seawater immersion. The results of this study will provide insight for an optimized material microstructure for increased resistance to sensitization and SCC.
11:30 AM
Stress Corrosion Cracking of Welded AA5059 Alloy: Rajesh Yadav1; Gajanan Chaudhari1; 1Indian Institute of Technology
Electrochemical behavior of friction stir welded (FSW), metal inert gas (MIG) welded and base AA5059H116 alloy samples is investigated. Cyclic polarization tests, Tafel tests, electrochemical impedance spectroscopy (EIS) tests, and slow strain rate tests (SSRT) are performed in 3.5 wt% NaCl solution. Fracture occurred at the interface of HAZ and TMAZ in FSWed zone specimen, and at the interface of HAZ and weld zone in MIG welded specimens. Results of SSRT tests done using different strain rates suggest that FSWed specimens are less susceptible to SCC than MIG welded specimens.