corrosion and fracture presentation
TRANSCRIPT
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CORROSION/ FRACTURE MECHANICS
LAB WORK
An experimental study on corrosion and mechanical behaviour ofZircaloy-4 under oxidation.
Presented by:
SHUKEIR Malik
RAI Ajit
PALLA Harin Reddy
BARI Md. Abdullah Al
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INTRODUCTION
OBJECTIVE : Behaviour of Zr-4 alloy under LOCA oxidationconditions.
Environment: In LOCA usually steam environment. Possible airoxidation under severe accidents:
- During shutdown when RCS is open to containment atmosphere.- During BDBA, core degrades and oxidation of outer core
regions.
Current Experiment: Behaviour of Zr-4 under air oxidation.- Corrosion study: Oxidation of Zr-4 in air, corrosion kinetics,
breakway oxidation.- Fracture Mechanics: Failure behaviour under mechanical loading.
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CORROSION STUDY- Objective:The objective is to study the oxidation of Zircaloy-
4 under the effect of air.
- Test conducted between 1273 K to 1473 K.
- Parameters:
Weight gain with respect to time and temperatures.
Oxide thickness evaluation with respect time and temperature.
- Conditions:Oxidation in air.
- Experimental protocols:
Measure the h, Di, Do of the samples. Degrease in acetone andclean in ethanol.
Weigh each sample three times.
Put samples in furnace for respective time and temperatures.Weigh the samples again after the furnace.
Polish the samples and study oxidation thickness for Di and
Do under SEM. 3
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EXPERIMENTAL RESULTS
Sampl
e No.
Tempe
rature(C)
Tim
e(sec)
Weight
Gain(g/m2)
1 300 45.37584
2 1000 900 59.35388
3 1800 78.16846
6 120 94.82662
7 1150 300 199.5630
8 900 479.2283
10 120 134.287
12 1200 300 255.7815
11 900 533.3813
13 1800 602.3297
y = 0,0373x + 17,724
y = -0,0002x2+ 0,7336x + 3,4465
y = -0,0003x2+ 0,8407x + 19,773
0
100
200
300
400
500
600
700
0 500 1000 1500 2000
WeightGain(g/m2)
Time (sec)
1000
1150
1200
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KINETIC ANALYSIS
Equation for Oxidation of Zirconium alloys:
Instead of n= we are taking a variable as we will see later on that we dont
follow just a parabolic trend but will also see linear and cubic trend of kinetics.
Thus we get,
After getting the value of k, we can plot ln k v/s ln (1/T). The slope of this plot will
give us the activation energy Ea as calculated from the following equation:
Which gives:
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KINETIC ANALYSIS
Temperature Time n Inference
1200 900 s 0.684 Between parabolic and linear: Mix
Diffusion
1150 900 s 0.8039 Between parabolic and linear: Mix
Diffusion
1000 1800 s 0.2982 Cubic: Diffusion
y = 0,2982x + 2,0978
y = 0,8039x + 0,7063
y = 0,684x + 1,6315
3
3,5
4
4,5
5
5,5
6
6,5
3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8
lndelM/S(g/m2)
ln t (s)
1000 deg C 1150 deg C 1200 deg C
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KINETIC ANALYSIS
y = 0,2982x + 2,0978
y = 0,5756x + 2,2141
3
3,5
4
4,5
5
5,5
6
6,5
7
3 3,5 4 4,5 5 5,5 6 6,5 7 7,5 8
lndelM/S(g/m2)
ln t (s)
1000 deg C 1200 deg C
Temperature Time n Inference
1200 1800 0.5756 Almost parabolic
1000 1800 0.3 Cubic :Diffusion main phenomenon 7
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KINETIC ANALYSIS- Using the equation ln (del M/S)- n ln t = ln kgiven in the previous slide, we can
calculate k.
Temp Time Ln (delM/S) n Ln k k
1000 1800 4.358866 0.2982 2.12369 8.3619
1150 900 6.172177 0.8039 0.70372 2.0212
1200 1800 6.400805 0.5756 2.08637 8.055
0
0,5
1
1,5
2
2,5
-7,32 -7,3 -7,28 -7,26 -7,24 -7,22 -7,2 -7,18 -7,16 -7,14
lnk
ln 1/T
3 points
2 points
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KINETIC ANALYSIS
CORROSION PHENOMENON
Case 1: When n=1 : Linear Kinetic reaction takes place. Faster phenomenon.
Catastrophic oxidation usually dominated by breakaway oxidation. In experiment
observed around 1150 deg C.
Case2: When n= 0.5 : Parabolic. Diffusion is the main phenomenon. Slower kinetics.
After 1200 deg C its observed value of n reaching parabolic limits.
Case 3: When n = 0.3: Cubic. Diffusion is the main phenomenon. Slowest kinetics.
Observed around 1000 deg C.
Anomalies with experimental and theoretical results??
- Theoretical results say : From 700 deg C to 1000 deg C, big transition from sub-
parabolic regime to linear fast kinetics. From 1100 deg C onwards, smoother
kinetics.
- These anomalies can be attributed to difference in the test setup and other important
factors (to be discussed later). 9
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SEM images
Before oxidation After oxidation 1150C 120 sec
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SEM 1000 C 15 min
External side Internal side
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SEM-1150 C, 15 min
External side Internal side
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SEM 1200 C, 15min
External side Internal side
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SEM 1200C, 15min
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Comparison with Theory
In the paper three alloys were investigated for airoxidation at high temperatures namely M5, Zirloand Zircaloy-4.
The tests were conducted in a commercialthermal balance. The gases (Ar,O2,N2,air) weresupplied via flow controllers.
The samples were of different lengths than whatwe did.
The temperature range was from 973k to 1853k.
Also some of the samples were tested with pre-oxidation
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COMPARISON WITH THEORY
y = 0,0373x + 17,724
y = -0,0002x2+ 0,7336x + 3,4465
y = -0,0003x2+ 0,8407x + 19,773
0
100
200
300
400
500
600
700
0 500 1000 1500 2000
WeightGain(g/
m2)
Time (sec)
1000
1150
1200
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Comparison with Theory
Paper
There are strong differencesbetween the three alloys andthe curves show a transition
from parabolic to linear oreven faster kinetics.
The transitions during thetests are caused by breakaway,i.e loss of the protective effect
of the oxide scale allowing fornitrogen access to the metaland subsequent formation ofZrN
Experimental
The mass gain increases with
Temperature.
Oxidation kinetics at thehighest Temperatures tends to
be more linear than parabolic,
which is most probably caused
by oxygen starvation
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Mass gain vs Temperature
Paper Lab
0
0,01
0,02
0,03
0,04
0,05
0,06
1000 1150 1200
Mass gain vs Temperature
Mass gain vs
Temperature
Temperature
M
as
s
G
ai
n
The slightly lower oxidation rates in air at 50K/min, may be due to
lower O2 concentration in air compared to pure O2.
Significant differences between the behaviour in air and O2 wereobserved for lowest heating rate of 5K/min.
After 1000 C, a significant acceleration of reaction of air is observed
at a higher T, its assumed that N comes into play, leading to
formation of ZrN and destabilization of oxide scale. 18
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SEMZr41273k 30min-paper External layer,1273k 30 minlab,
55micrometer thickness
The degradation of the oxide scale is caused by formation of ZrN at the metal-oxide boundary
which converts to oxide again with growing scale by fresh air flowing from external surface to
metal.
The region is mixed with ZrO2 and ZrN at the metal-oxide boundary, its thinner, but is porous
and non protective.Dark area is ZrO2/ZrN mixture
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Fracture Mechanics study
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Outlines
Objectives
Our Sample
Experimental Set-up
Variation from ideal conditions
Variation of oxidation thickness withtemperature
SEM observation of oxidized layer
Load Vs Displacement curve Maximum energy Vs Load curve
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Objectives
Simulate LOCA (loss of coolant accident) tests on Zircaloy-4
cladding.
Carry out mechanical tests after oxidation on same cladding.
Mechanical property evaluations and compare.
Analyse microstructure and evaluate the absorbed contents(oxygen).
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Our Sample:
Sample dimensions:
Outer diameter: 9.5 mm, Thickness: 0.75 mm,Height: 15 mm (approx.)
Materials: Zircaloy-4 (Zr-1.3Sn-0.2Fe-0.1Cr) Total 6 samples
Total duration of time for each sample: 300seconds
Temperatures of Irradiation:1000,1100,1125,1150,1175 and 1200 C
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Deviation from Ideal Conditions:
Temperature measurement method: No thermocoupleused, no axial temperature recorded. Only the furnacetemperature.
Air oxidation only not the flowing steam oxidation.
No intermediate temperature, only one temperatureheated and then cooled.
Air cooling instead of water quenching.
Sample oxidizing at different temperatures but for sametime (1-Dimensional failure evaluation only) no time
variation. Only ring compression mechanical test no 3-points bend
test.
No gas analysis has done.
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Variation of oxidation thickness
with temperature:
0
50
100
150
200
250
300
950 1000 1050 1100 1150 1200 1250
Oxidethickness(m)
Temperature(K)
Oxide Layer Thickness
Total Oxide thickness
Figure : Oxide layer thickness Vs temperature
graph
Here the thickness is measured from SEM observation
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0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
950 1000 1050 1100 1150 1200 1250
Massingrams
Temperature in deg C
Mass gain with temperatures
Similar types of trend we also found in mass gain before
and after oxidation
Figure : Mass difference Vs temperature graph
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SEM observation of oxidation layer
Figure: Fractography after
compression test at 1125 CFigure: Schematic
illustrations of
intermetallic precipitation
in oxide layers 27
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At high temperature near 1200 C, the behviour of Zircaloy
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Mechanical test:
Failure behaviour under mechanical test.
Ring Compression test.
Roughly 15 mm each specimen, compressed at
1 mm/min.
Three main curves:
Load Displacement curves. Absorbed Energy.
Maximum Load.
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Mechanical Properties
0
20
40
60
80
100
120
0 1 2 3 4 5 6
Load(Kgf)
Displacement (mm)
Load Displacement Diagram
1000 C
1100 C
1125 C
1150 C
1175 C
1200 C
Cladding Oxidized at 1000 & 1100 C exhibited a ductile compression.
Oxidation over 1100 C, cladding showed an abrubt load drop, then plastic
deformation.
This load drop is due to Fracture of the brittle oxide outside the cladding surface.30
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Mechanical Properties
0
10
20
30
40
50
60
0 0,5 1 1,5 2
Load(Kgf)
Displacement (mm)
Load Displacement Diagram
1125 C
1150 C
1175 C
1200 C
0
20
40
60
80
100
120
0 1 2 3 4 5 6
Load(Kgf)
Displacement (mm)
Load Displacement Diagram
1000 C
1100 C
When the load drop occured the
prior B-layer was so stable andcan sustain an additional
compression load.
Additional load after load drop
decreased gradually with
oxidation temperature forT=1000, 1100 C.
Beyond 1125 C, the thickness of
the prior-layer was so thin, and
brittle; drop at the elastic region.
Note: Sawtooth patern, due to
maintained cylindrical shape with
deformation.
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Mechanical Properties
y = -2E-09x4+ 1E-06x3- 0.0002x2+ 0.0107x + 0.2224
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0 20 40 60 80 100 120 140 160 180
Displacement(mm)
Load (Kgf)
Machine Stiffness
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Mechanical Properties
0
20
40
60
80
100
120
140
160
180
200
950 1000 1050 1100 1150 1200 1250
Energy(Kgf.mm)
Oxidation temperature (C)
Absorbed Energy
Oxidized for5 min
Absorbed Energy= Area under the curve.
Abrubt decrease between 11001125. (for them 1100 1150) more precice.
At 1200 C So high temperature that result in an accelerated Oxygen diffusion,
O content increase cause Prior-B causing Embrittlement. 33
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Mechanical Properties:
0
20
40
60
80
100
120
950 1000 1050 1100 1150 1200 1250
Load(N)
Oxidation tamperature (C)
Maximum Load
Oxidized for 5min
DBTT
Load drop by fracture of Oxide surface occured at the plastic region when
oxidized at T up to 1125 C.
Load drop at Elastic region, when Oxidized at high temperature.
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Mechanical Properties:
0
0,2
0,4
0,6
0,8
1
1,2
1,4
950 1000 1050 1100 1150 1200 1250
Displace
ment(mm)
Oxidation temperature (C)
Maximum Displacement
Oxidized for
5 min
Maximum displacement decrease with increasing temperature.(at first load
drop).
In the paper, Max displacement is Contiuously decreasing not the same
case, where a drop occured. 35
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Conclusion:
Unable to compute the activation energy due to lack of
samples, and anomalies between experimental and
theoretical set up.
Improper polishingdue to brittle behaviour at high
temperature. Oxidation thickness increase with temperature.
Unability to observe the dissolved oxygen due to lack of
facility. Ductile to brittle transition at around 1100 C.
Fracture at the elastic region for elevated temperatures.
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