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Transmutation Sciences Materials (TRP) Transmutation Research Program Projects
6-18-2003
Environment-Induced Degradation and Crack-Growth Studies of Environment-Induced Degradation and Crack-Growth Studies of
Candidate Target Materials: Annual Progress Report (May 2002 – Candidate Target Materials: Annual Progress Report (May 2002 –
May 2003) May 2003)
Ajit K. Roy University of Nevada, Las Vegas, [email protected]
Brendan O'Toole University of Nevada, Las Vegas, [email protected]
Follow this and additional works at: https://digitalscholarship.unlv.edu/hrc_trp_sciences_materials
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Repository Citation Repository Citation Roy, A. K., O'Toole, B. (2003). Environment-Induced Degradation and Crack-Growth Studies of Candidate Target Materials: Annual Progress Report (May 2002 – May 2003). 1-8. Available at:Available at: https://digitalscholarship.unlv.edu/hrc_trp_sciences_materials/49
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Annual Progress Report (May 2002 – May 2003)
Environment-Induced Degradation and Crack-Growth Studies of
Candidate Target Materials
TRP Task-4
Principal Investigator Ajit K. Roy, Ph.D.
Co-Principal Investigator Brendan J. O’Toole, Ph.D.
Investigators
David W. Hatchet, Ph.D. Zhiyong Wang, Ph.D.
Mohammad K. Hossain Ramprashad Prabhakaran
Sudheer Sama Phani P. Gudipati
Venkataramakrishnan Selvaraj
University of Nevada, Las Vegas
June 18, 2003
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Environment-Induced Degradation and Crack-Growth Studies of Candidate Target Materials
Introduction As indicated in the original proposal, the primary objective of this task is to evaluate the effect of hydrogen on environment-assisted cracking of candidate target materials for applications in spallation-neutron-target (SNT) systems such as accelerator production of tritium (APT) and accelerator transmutation of waste (ATW). The materials selected for evaluation and characterization are martensitic stainless steels including Alloy HT-9, Alloy EP 823 and Type 422 stainless steel. The susceptibility to stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of these materials are being evaluated in aqueous environments of interest using tensile specimens under constant load and slow-strain-rate (SSR) conditions. Further, the localized corrosion behavior of these alloys is being evaluated by electrochemical polarization techniques. The extent and morphology of cracking and localized corrosion of the tested specimens are being determined by optical microscopy and scanning electron microscopy (SEM). The concentration of hydrogen resulting from cathodic charging will be analyzed by secondary ion mass spectrometry (SIMS). More recently, this experimental program has been refocused to evaluate the effect of molten LBE on the corrosion behavior of similar target materials in the presence of oxygen. Since the Materials Performance Laboratory (MPL) currently cannot accommodate this type of testing, the lead-bismuth-eutectic (LBE) loop at the Los Alamos National Laboratory (LANL) will be used to contain the stressed test specimens to evaluate the SCC, HE, and localized corrosion (pitting and crevice) behavior in the molten LBE environment. Since the magnitude of the applied load/stress during these tests cannot be monitored or controlled (as in conventional SCC/HE experiments) in the LBE environment, the test specimens will be self-loaded. Two types of specimen configurations, namely C-ring and U-bend, are being used to perform these desired experiments. The stress of principal interest in both types of specimen is the circumferential stress. SCC tests using these types of self-loaded specimens are also being performed in aqueous environments having neutral and acidic pH values at ambient and elevated temperatures. Personnel The current project participants are listed below. Principal Investigator (PI): Dr. Ajit K. Roy Co-PI: Dr. Brendan J. O’Toole Department of Mechanical Engineering, UNLV Roy: Phone: (702) 895-1463 email: [email protected] O’Toole: Phone: (702) 895-3885 email: [email protected] Investigators (UNLV): Dr. David W. Hatchet, Department of Chemistry Dr. Zhiyong (John) Wang, Department of Mechanical Engineering Mr. Mohammad K. Hossain, Department of Mechanical Engineering
Mr. Ramprashad Prabhakaran, Department of Mechanical Engineering Mr. Sudheer Sama, Department of Mechanical Engineering
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Mr. Venkataramakrishnan Selvaraj, Department of Mechanical Engineering Mr. Phani P Gudipati, Department of Mechanical Engineering
Hatchet: Phone: (702) 895-3509 email: [email protected] Wang: Phone: (702) 895-3442 email: [email protected] Hossain: Phone: (702) 895-1027 email: [email protected]
Prabhakaran: Phone: (702) 895-1027 email: [email protected] Sama: Phone: (702) 895-1027 email: [email protected] Selvaraj: Phone: (702) 895-1027 email: [email protected]
Gudipati: Phone: (702) 895-1027 email: [email protected] Collaborator (DOE): Dr. Ning Li, LANL, New Mexico Phone: (505) 665-6677 email: [email protected]
Dr. Stuart A. Maloy, LANL, New Mexico Phone: (505) 667-9784 email: [email protected]
Accomplishments
• Ambient temperature mechanical properties of Alloys EP-823, HT-9 and Type 422 Stainless Steel (SS) were evaluated by calibrated MTS equipment using smooth and notched tensile specimens.
• A significant number of SCC tests using calibrated proof rings and smooth tensile specimens of
martensitic Type 422 SS, and Alloys EP-823 and HT-9 have been completed in both neutral and acidic aqueous environments under constant-load (CL) conditions at ambient temperature and 90°C. The results of CL SCC testing indicate that neither Alloy EP-823 nor Type 422 SS showed failure in neutral environment at applied stresses approaching 90 and 95 percent of the material’s YS value at ambient temperature and 90oC. CL SCC testing of Alloy HT-9 in a similar environment at both temperatures is currently in progress. Data also indicate that failures were observed in all three materials when tested in the 90oC acidic environment at applied stresses corresponding to the 95 percent of the materials’ YS values. Further, Type 422 SS exhibited failure in a similar environment at an applied stress equivalent to 90, 85 and 80 percent of its YS value, as shown in Figure 1. Additional tests are ongoing at reduced stresses to determine the threshold stress (σth) for SCC. Simultaneously, tests are being conducted using the notched tensile specimens.
• SCC testing using slow-strain-rate (SSR) technique has been completed in both aqueous
environments at ambient temperature, 60 and 90oC involving smooth and notched tensile specimens of all three martensitic alloys. A typical load versus displacement curve is shown in Figure 2, showing the effect of temperature. The results of SSR testing of Type 422 SS are illustrated in Figure 3, elucidating the effects of temperature, solution pH and specimen geometry (smooth versus notched gage section) on % elongation (% El), % reduction in area (% RA), time-to-failure (TTF) and failure stress (σf). These data indicate that, for the smooth specimen, the ductility parameters, TTF and σf were significantly reduced in the 90oC acidic solution, showing a synergistic influence of pH and temperature on the cracking susceptibility
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of this alloy. The presence of notch in the test specimen further reduced the TTF and the extent of ductility in terms of %El and %RA. However, the magnitude of σf in this material was increased to some extent in the presence of a notch primarily due to a smaller area at the root of the notch. Similar effects of temperature, pH, and specimen geometry on cracking susceptibility were observed with Alloys EP-823 and HT-9.
• Extensive efforts were made to analyze the fracture modes in all broken specimens. Based on
these fractographic evaluations, it appears that the primary failure mode at the gage section of specimens tested in neutral environment at both test temperatures was ductile showing dimpled microstructures, as shown in Figure 4A. On the contrary, the specimens tested in acidic environment showed intergranular and/or transgranular brittle failures at both test temperatures (Figures 4B, 4C and 4D). However, the extent of cracking was more severe at the elevated temperature. The metallographic evaluation of the secondary cracks along the gage section of the broken specimen by optical microscopy revealed branching of cracks, as illustrated in Figure 5.
• The susceptibility of all three alloys to pitting and crevice corrosion in both neutral and acidic
aqueous solutions was determined by performing cyclic potentiodynamic polarization (CPP) experiments using EG&G Model 273A Potentiostats. A three-electrode polarization technique was used. At the onset, the corrosion potential (Ecorr) was measured with respect to a silver/silver chloride (Ag/AgCl) electrode, followed by forward and reverse potential scans at the ASTM- specified rate of 0.17 mV/sec. The magnitudes of the critical pitting potential (Epit) and the protection potential (Eprot), if any, were determined from the CPP diagram. The preliminary data indicate that the corrosion potential and the critical pitting potential became more active (negative) with increasing temperature and reduced pH of the test solution, as expected, as shown in Figures 6.
• Additional tensile specimens have been machined using bars heat-treated at MPL by a qualified
machine shop.
• SCC testing using C-ring and U-bend specimens of Alloys HT-9 and EP-823 is in progress in acidic solution both in the presence and absence of air at ambient temperature. Elevated temperature tests are also being planned. Similar types of specimens will be tested at LANL in the molten lead-bismuth-eutectic environment.
• Three technical papers have been presented at three conferences: IHLRWM conference (Las
Vegas, NV), ECS conference (Paris, France) and ANS conference (San Diego, CA). In addition, multiple oral presentations were made by graduate students involved in this research project at the ANS Student Conference (Berkeley, CA). A poster presentation was also made by a graduate student at the SINS-JINS-NICEST conference (Oak Ridge, TN). Another technical paper will be presented in November at the Materials Science & Technology (MS&T) 2003 conference (Chicago, IL)
Problems
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No problems are anticipated. Status of Funds Expenditures incurred during the second year are within the target amount allocated. Plans for Year 3 • Perform SCC/HE testing of all three types of martensitic stainless steels under cathodic potential. • Continue heat treatments and specimen preparations. • Perform localized corrosion testing using electrochemical techniques at elevated temperatures. • Perform metallurgical evaluations including microstructural characterizations by optical microscopy. • Conduct failure analyses using SEM. • Prepare technical/scientific papers for presentations for future conferences and publications.
Figure 1: Applied Stress versus Time-To-Failure
80
85
90
95
100
0 50 100 150 200 250 300 350 400
Time-To-Failure (hours)
App
lied
Stre
ss (%
YS)
Type 422 SSAlloy HT-9
CL Tests, Environment : 90°C , Acidic Solution ( pH : 2 - 3 )
5
Figure 2: Typical Load versus Displacement Curve
Figure 3: Effect of pH, Temperature and Notch on %RA, %EL, σf and TTF for Type 422 SS
Type 422 Stainless Steel
0
2000
4000
6000
8000
0 0.04 0.08 0.12 0.16 0.2
Displacement (Inches)
Load
(Pou
nds)
Acidic Solution, 30°C Acidic Solution, 90°C
10.52
16.81
1.2851.4851.61 1.515
16.73
19.05
0
5
10
15
20
25
0 20 40 60 80 100Temperature (°C)
% E
long
atio
n
10.52
16.81
1.2851.4851.61 1.515
16.73
19.05
0
5
10
15
20
25
0 20 40 60 80 100Temperature (°C)
% E
long
atio
n
3.875
11.9
17.5
4.133.974.25
17.7
19.09
0
5
10
15
20
25
0 20 40 60 80 100Temperature (°C)
Tim
e to
Fai
lure
(hou
rs)
117
174181.88204.92
213.56 196.03
165
187
0
50
100
150
200
250
0 20 40 60 80 100Temperature (°C)
Failu
re S
tress
(ksi
)
6
4A. Alloy EP-823 tested in 90°C SAW Environment 4B. Alloy HT-9 tested in 90°C SAWM Environment
4C. Type 422 SS tested in 30°C SAWM Environment 4D. Type 422 SS tested in 90°C SAWM Environment
Figure 4: SEM Micrographs of Cracked Specimens
5A. Alloy EP-823 (40X, as polished) 5B. Type 422 SS (40X, as polished)
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5C. Alloy EP-823 (20X, etched) 5D. Type 422 SS (20X,etched)
Figure 5: Optical Micrographs in 90°C Acidic Environment
422 SS : Critical Potential Vs Temperature
-0.6-0.5-0.4-0.3-0.2-0.1
00.10.2
0 10 20 30 40 50 60 70
Temperature (°C)
Crit
ical
Pot
entia
l (V)
Ecorr:422 SS in SAWM Epit: 422 SS in SAWMEcorr:422 SS in SAW Epit:422 SS in SAW
Figure 7: CPP Data
E(m
V)
I(log(A/cm^2)
-100 -200 -300 -400 -500 -600 -700
0 100 200 300 400 500
-1 -2 -3 -4 -5 -6 0
CPP Curve: 422 SS, 30°°°°C, acidic solution, 0.17mV/sec
Epit = - 116 mV
Eprot = - 196 mV
Ecorr = - 506 mV
E(m
V)
I(log(A/cm^2))
-100
-200
-300
-400
-500
-600
-700
0
100
200
300
400
500
-1-2-3-4-5 0
CPP Curve:422 SS, 60°°°°C, acidic solution, 0.17mV/sec
Epit = - 191 mV
Eprot = - 211 mV
Ecorr = - 531 mV
