MP98t -1.3 V - University of Virginia · strengthened by spherical Ni₃(Al,Ti),...
1
NRL HS -950 mV Kj (MPa sqrt. m) 0 20 40 60 80 100 da/dt (mm/s) 1e-9 1e-8 1e-7 1e-6 1e-5 1e-4 dK/dt = 0.12 dK/dt = 0.25 dK/dt = 0.36 dK/dt = 1.28 dK/dt = 2.39 dK/dt = 4.36 0.12 RL 0.25 RL 0.36 RL 1.28 RL 2.39 RL 4.36 RL [2] Increasing K-rate MP98t -1.3 V K (MPa sqrt. m) 0 20 40 60 80 100 120 140 160 da/dt (mm/s) 1e-8 1e-7 1e-6 1e-5 1e-4 Increasing K-rate Increasing K-rate Sample Description: Single edge notch tension (SENT) specimen, the load was applied longitudinally, along the rolling direction of MP98t. Measurement Method: Direct current potential difference (dcPD) is used to measure active crack growth. Environment: 0.6 M NaCl with a constant applied electrical potential (V SCE ). Experiment: A tensile slow rising displacement test with a constant MPa m hr . The applied dK dt changes with each test. Fractography: The fracture surface is analyzed in the SEM. Data Analysis: The crack growth rate da dt is determined. Material corrections are applied: NRL HS creates a large plastic zone relative to the specimen size so elastoplastic K J is used. Comparison: Test results are compared to each other and computational models to determine trends. Experimental Approach Strain Rate Effects on the Stress Corrosion Cracking Behavior of Ni- and Co- Based Superalloys for Marine Applications Allison Popernack and J.T. Burns Center for Electrochemical Science and Engineering, Department of Materials Science and Engineering, University of Virginia Introduction and Motivation Objectives References Monel K-500 MP98t 1. Further quantify dK dt effects, focusing on very high and low dK dt values to determine if plateaus exists. 2. Preliminary testing of NRL HS at -850 mV SCE shows no evidence of SCC at a dK dt = 0.33 MPa m hr . However, this potential could be useful for determining if a cracking can be induced at different dK dt . This testing could give insight into what mechanism governs hydrogen environmentally assisted cracking (HEAC). 3. Use the quantitative data and mechanistic insights to inform experiment testing protocols for engineering relevant loading rate conditions. 1. Use LEFM experiments to quantify the effect of dK dt on the K th and da dt II for two different marine alloys at relevant electrochemical polarization(s) 2. Use experimental data to provide mechanistic insight for the any dK dt dependent SCC behavior 3. Inform practical testing protocols to ensure accurate and conservative quantification of the SCC behavior MP98t is a Co-Ni-Cr solid solution that has been cold worked and precipitation hardened [4]. MP98t has an elongated grain structure parallel to the rolling direction (RD). 1. MP98t shows decreases in trends with increasing . The magnitude is material dependent. 2. NRL HS and MP98t show IGSCC and IG/TG-SCC, respectively. These morphologies are consistent over the full range of values examine. This suggests that there is not a fundamental change in the mechanism as varies. 3. The plastic resolution limit for dcPD does not scale linearly across all K-rates. Materials [1] R. P. Gangloff, H. M. Ha, J. T. Burns, and J. R. Scully, “Measurement and modeling of hydrogen environment -assisted cracking in monel K-500,” Metall. Mater. Trans. A Phys. Metall. Mater. Sci., vol. 45, no. 9, pp. 3814–3834, 2014. [2] Somerday, Young and Gangloff., Crack tip Mechanics Effects on Environment-assisted Cracking of Beta-Titanium Alloys in Aqueous NaCl. Fatigue & Fracture of Engineering Materials & Structures, 23: 39-58, 2000 [3] Nickel-Copper-Aluminum Alloy, Wrought (UNS N05500), QQ-N-286G: Department of the Navy, 2000. [4] B. P. Focht, E. M. and L’Heureux, “Development of Modified Alloy MP159 Bar for 150 ksi Marine Grade Fasteners,” West Bethesda, MD, 2002. Monel K-500 was tested at -950 mV SCE with dK dt = 0.33 MPa m hr . SCC only occurred at this potential so further testing was pursued. To remove the additional increase due to plastic effects, the resolution limit (RL) for each dK dt was subtracted from the data. The scaling plasticity effects must be removed in order to see true crack growth trends. Both materials examined are solid solutions that have been strengthened by spherical Ni₃(Al,Ti), γ’, precipitation. Monel K-500 was designed to maximize the strength limits listed in material specification QQ-N-286 [3]. Monel K-500 has an equiaxed grain structure and many notable failures due to intergranular stress corrosion cracking (IGSCC) in service conditions. Material\ Attribute Elastic Modulus (GPa) Yield Strength (MPa) Applied Potential (V SCE ) Monel K-500 188 910 -0.950 MP98t 224 1470 -1.30 wt% Monel K-500 MP98t Ni 63.44 26.61 Co 0.02 34.95 Cu 30.74 - Cr - 18.87 Al 3.2 0.18 Fe 0.91 8.58 Mo - 7.38 Ti 0.57 2.85 Conclusions Future Work Results The plastic resolution limit does not scale linearly across all K-rates. appears to increase with . is independent of . A maximum may be apparent. MP98t shows mixed IG and transgranular cracking (TG-SCC). After a short Mode I crack extension, the crack deflected to ≈ 45°, this occurred on all samples tested at -1.30 V SCE . Post-test corrections were made to the K and da dt calculations to reflect the changes due to mixed mode fracture. Discontinuities in the graph below depict the K of deflection. Precrack SCC Crack Direction RD B1 fracture, side view Grain boundaries of unstrained MP98t, determined by EBSD Error increases in the dcPD readings at very high K, >70 MPa m, possibly due to large scale plasticity. Remove plastic effects The reason for deflection is not conclusively established, but is directionally consistent with anisotropy in grain size (EBSD) and tensile properties. dcPD calculates crack growth by comparing the change in resistance through the sample over time with a constant magnitude current. Crack growth and plastic deformation can manifest as increased resistance. To determine the resistance experienced by a sample due to plasticity, a resolution limit (RL) test is run at a constant dK dt in a non-cracking environment. The RL is linearly scalable with dK dt . Environmental Cell SCE Sample dcPD Counter Electrode Working Electrode Masking Lacquer Notch Applied Load Applied Load 0.20 mm ND RD MP98t EBSD image 0.20 mm dK/dt = 0.2 dK/dt = 0.33 dK/dt = 1.0 dK/dt = 2.0 0.2 RL 0.33 RL 1.0 RL 2.0 RL This project is funded by the DoD Corrosion Office through USAFA-CASTLE under Contract # W911NF-14-2-0005. dK/dt (MPa sqrt.m /hr) 0.0 0.5 1.0 1.5 2.0 da/dt II (mm/s) 1e-6 1e-5 1e-4 Kth (MPa sqrt.m) 20 25 30 35 40 45 50 55 60 dK/dt vs da/dt II dK/dt vs Kth MP98t da dt II and K th comparison Acknowledgements Possible Mechanisms Knowledge Gap: What is the effect of on the SCC behavior for marine critical alloys? dK dt = 0.12 MPa m hr dK dt = 2.39 MPa m hr dK dt = 0.33 MPa m hr dK dt = 2.0 MPa m hr Monel K-500 data for samples tested at -850 mV SCE , 0.33 MPa m hr showed identical K vs da dt II to the resolution limit testing done in dry N 2 . The fracture surfaces were also extremely similar. Marine fastener materials have exhibited IG-SCC failures in sea- water environments when exposed to polarization from cathode protection systems. Fracture mechanics characterization and life estimations offers a next-generation means by which to manage these long life failures. Specifically, IG-SCC metrics (threshold stress intensity (K th ) and Stage II crack growth rate ( da dt II )) can be established using laboratory testing and used to inform engineering decisions via the similitude concept [1]. Critically, prior efforts have established that K th and da dt II can be a . strong function of loading rate. An understanding of this behavior is necessary for accurate characterization and structural management of marine alloys (MP98t and Monel K-500) susceptible to IG-SCC. Specifically, it is necessary to ensure that IG-SCC metrics established via laboratory testing are pertinent to in-service loading rate conditions [1]. Crack Tip Strain Rate with Barrier Rupture - Some barrier at the crack tip develops and blocks additional H from entering. At a sufficiently high loading rate, this barrier is continually ruptured, creating a fresh receptive surface. Concurrent Plasticity- Increased crack tip work hardening due to simultaneous H adsorption and strain- induced plasticity [1]. These mechanisms may have some dK dt limited step that causes the da dt II plateaus. Low exhibits a distinct IG morphology, as increase the amount of ductile features increases, consistent with the plasticity contributions shown above. Fracture surface morphology is independent of . The plastic effects collected in conjunction with crack growth by dcPD must further analyzed for true crack growth rates to be determined. This work is in progress and has thus far seen that the resolution limit does not scale linearly with dK dt > 1.0 MPa m hr in Monel K-500.
Transcript of MP98t -1.3 V - University of Virginia · strengthened by spherical Ni₃(Al,Ti),...
NRL HS -950 mV
Kj (MPa sqrt. m)
0 20 40 60 80 100
da
/dt (m
m/s
)
1e-9
1e-8
1e-7
1e-6
1e-5
1e-4
dK/dt = 0.12
dK/dt = 0.25
dK/dt = 0.36
dK/dt = 1.28
dK/dt = 2.39
dK/dt = 4.36
0.12 RL
0.25 RL
0.36 RL
1.28 RL
2.39 RL
4.36 RL
[2]
Increasing
K-rate
MP98t -1.3 V
K (MPa sqrt. m)
0 20 40 60 80 100 120 140 160
da/d
t (m
m/s
)
1e-8
1e-7
1e-6
1e-5
1e-4
Increasing
K-rateIncreasing
K-rate
Sample Description: Single edge notch tension
(SENT) specimen, the load was applied
longitudinally, along the rolling direction of
MP98t.
Measurement Method: Direct current potential
difference (dcPD) is used to measure active
crack growth.
Environment: 0.6 M NaCl with a constant
applied electrical potential (VSCE).
Experiment: A tensile slow rising displacement
test with a constant𝐝𝐊
𝐝𝐭
MPa m
hr. The applied
dK
dtchanges with each test.
Fractography: The fracture surface is analyzed
in the SEM.
Data Analysis: The crack growth rateda
dtis
determined. Material corrections are applied:
NRL HS creates a large plastic zone relative
to the specimen size so elastoplastic KJ is
used.
Comparison: Test results are compared to each
other and computational models to determine
trends.
Experimental Approach
Strain Rate Effects on the Stress Corrosion Cracking Behavior of Ni- and Co- Based Superalloys for
Marine Applications
Allison Popernack and J.T. BurnsCenter for Electrochemical Science and Engineering, Department of Materials Science and Engineering, University of Virginia
Introduction and Motivation
Objectives
References
Monel K-500 MP98t
1. Further quantifydK
dteffects, focusing on very high and low
dK
dtvalues to determine if plateaus exists.
2. Preliminary testing of NRL HS at -850 mVSCE shows no evidence of SCC at adK
dt= 0.33 MPa m
hr.
However, this potential could be useful for determining if a cracking can be induced at differentdK
dt.
This testing could give insight into what mechanism governs hydrogen environmentally assisted
cracking (HEAC).
3. Use the quantitative data and mechanistic insights to inform experiment testing protocols for
engineering relevant loading rate conditions.
1. Use LEFM experiments to quantify the effect ofdK
dton the Kth and
da
dtIIfor two different marine
alloys at relevant electrochemical polarization(s)
2. Use experimental data to provide mechanistic insight for the anydK
dtdependent SCC behavior
3. Inform practical testing protocols to ensure accurate and conservative quantification of theSCC behavior
MP98t is a Co-Ni-Cr solid solution that has been cold worked and
precipitation hardened [4]. MP98t has an elongated grain structure
parallel to the rolling direction (RD).
1. MP98t shows decreases in 𝐊𝐭𝐡 trends with increasing𝐝𝐊
𝐝𝐭. The magnitude is
material dependent.
2. NRL HS and MP98t show IGSCC and IG/TG-SCC, respectively. These
morphologies are consistent over the full range of𝐝𝐊
𝐝𝐭values examine. This
suggests that there is not a fundamental change in the mechanism as𝐝𝐊
𝐝𝐭varies.
3. The plastic resolution limit for dcPD does not scale linearly across all K-rates.
Materials
[1] R. P. Gangloff, H. M. Ha, J. T. Burns, and J. R. Scully, “Measurement and modeling of hydrogen environment-assisted cracking in monel K-500,” Metall. Mater.
Trans. A Phys. Metall. Mater. Sci., vol. 45, no. 9, pp. 3814–3834, 2014.
[2] Somerday, Young and Gangloff., Crack tip Mechanics Effects on Environment-assisted Cracking of Beta-Titanium Alloys in Aqueous NaCl. Fatigue & Fracture
of Engineering Materials & Structures, 23: 39-58, 2000
[3] Nickel-Copper-Aluminum Alloy, Wrought (UNS N05500), QQ-N-286G: Department of the Navy, 2000.
[4] B. P. Focht, E. M. and L’Heureux, “Development of Modified Alloy MP159 Bar for 150 ksi Marine Grade Fasteners,” West Bethesda, MD, 2002.
Monel K-500 was tested at -950 mVSCE withdK
dt= 0.33 MPa m
hr. SCC only occurred at this potential so
further testing was pursued. To remove the additional increase due to plastic effects, the resolution limit
(RL) for eachdK
dtwas subtracted from the data. The scaling plasticity effects must be removed in order to
see true crack growth trends.
Both materials examined are solid solutions that have been
strengthened by spherical Ni₃(Al,Ti), γ’, precipitation.
Monel K-500 was designed to maximize the strength limits listed in
material specification QQ-N-286 [3]. Monel K-500 has an equiaxed
grain structure and many notable failures due to intergranular
stress corrosion cracking (IGSCC) in service conditions.
Material\ AttributeElastic Modulus
(GPa)
Yield Strength
(MPa)
Applied Potential
(VSCE )
Monel K-500 188 910 -0.950
MP98t 224 1470 -1.30
wt% Monel K-500 MP98t
Ni 63.44 26.61
Co 0.02 34.95
Cu 30.74 -
Cr - 18.87
Al 3.2 0.18
Fe 0.91 8.58
Mo - 7.38
Ti 0.57 2.85
Conclusions Future Work
Results
The plastic resolution limit does not scale linearly across all K-rates.
𝐝𝐚
𝐝𝐭𝐈𝐈appears to increase with
𝐝𝐊
𝐝𝐭. 𝐊𝐭𝐡 is independent of
𝐝𝐊
𝐝𝐭. A maximum
𝐝𝐚
𝐝𝐭𝐈𝐈may be apparent.
MP98t shows mixed IG and transgranular cracking
(TG-SCC). After a short Mode I crack extension, the
crack deflected to ≈ 45°, this occurred on all
samples tested at -1.30 VSCE. Post-test corrections
were made to the K andda
dtcalculations to reflect the
changes due to mixed mode fracture. Discontinuities
in the graph below depict the K of deflection.
Precrack
SCC
Crack Direction
RD
B1 fracture, side view
Grain boundaries of unstrained
MP98t, determined by EBSD
Error increases in the dcPD readings at very high K, >70 MPa m, possibly due to large scale plasticity.
Remove
plastic effects
The reason for deflection is not conclusively
established, but is directionally consistent with
anisotropy in grain size (EBSD) and tensile
properties.
dcPD calculates crack growth by comparing the
change in resistance through the sample over time
with a constant magnitude current.
Crack growth and plastic deformation can manifest
as increased resistance.
To determine the resistance experienced by a
sample due to plasticity, a resolution limit (RL) test is
run at a constantdK
dtin a non-cracking environment.
The RL is linearly scalable withdK
dt.
Environmental Cell
SCE
Sample
dcPD Counter
Electrode
Working
ElectrodeMasking
Lacquer
Notch
Applied Load
Applied Load
0.20 mm
ND
RDMP98t EBSD image
0.20 mm
dK/dt = 0.2
dK/dt = 0.33
dK/dt = 1.0
dK/dt = 2.0
0.2 RL
0.33 RL
1.0 RL
2.0 RL
This project is funded by the DoD Corrosion Office through USAFA-CASTLE under Contract # W911NF-14-2-0005.
dK/dt (MPa sqrt.m /hr)
0.0 0.5 1.0 1.5 2.0
da/d
t II
(mm
/s)
1e-6
1e-5
1e-4
Kth
(MP
a s
qrt.m
)
20
25
30
35
40
45
50
55
60
dK/dt vs da/dt II
dK/dt vs Kth
MP98t da
dtIIand Kth comparison
AcknowledgementsPossible Mechanisms
Knowledge Gap: What is the effect of 𝐝𝐊
𝐝𝐭on the SCC behavior for marine critical alloys?
dK
dt= 0.12 MPa m
hrdK
dt= 2.39 MPa m
hr
dK
dt= 0.33 MPa m
hrdK
dt= 2.0 MPa m
hr
Monel K-500 data for samples tested at -850 mVSCE, 0.33 MPa mhr showed identical K vs
da
dtIIto the
resolution limit testing done in dry N2. The fracture surfaces were also extremely similar.
Marine fastener materials have exhibited IG-SCC failures in sea-
water environments when exposed to polarization from cathode
protection systems. Fracture mechanics characterization and life
estimations offers a next-generation means by which to manage
these long life failures. Specifically, IG-SCC metrics (threshold
stress intensity (Kth) and Stage II crack growth rate (da
dtII)) can be
established using laboratory testing and used to inform
engineering decisions via the similitude concept [1].
Critically, prior efforts have established that Kth andda
dtIIcan be a
.strong function of loading rate. An understanding of this behavior is necessary for accurate
characterization and structural management of marine alloys (MP98t and Monel K-500) susceptible to
IG-SCC. Specifically, it is necessary to ensure that IG-SCC metrics established via laboratory testing
are pertinent to in-service loading rate conditions [1].
Crack Tip Strain Rate with Barrier Rupture - Some barrier at the crack tip develops and blocks
additional H from entering. At a sufficiently high loading rate, this barrier is continually ruptured, creating a
fresh receptive surface.
Concurrent Plasticity- Increased crack tip work hardening due to simultaneous H adsorption and strain-
induced plasticity [1].
These mechanisms may have somedK
dtlimited step that causes the
da
dtIIplateaus.
Low𝐝𝐊
𝐝𝐭exhibits a distinct IG morphology, as
𝐝𝐊
𝐝𝐭increase the amount of ductile features increases,
consistent with the plasticity contributions shown above.
Fracture surface morphology is independent of 𝐝𝐊
𝐝𝐭.
The plastic effects collected in conjunction with crack growth
by dcPD must further analyzed for true crack growth rates to
be determined.
This work is in progress and has thus far seen that the
resolution limit does not scale linearly withdK
dt> 1.0 MPa m
hr
in Monel K-500.
