corrosion and fracture presentation

8/13/2019 Corrosion and Fracture presentation

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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

4


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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

6


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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

8


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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


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SEM 1200 C, 15min


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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

16


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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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0

10

20

30

40

50

60

0 0,5 1 1,5 2

Load(Kgf)

Displacement (mm)


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)


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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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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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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corrosion and fracture presentation

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