Characterization of Void Growth in High Temperature Fatigued

Copper through USANS

Guangjun Cheng Stephen Fenimore

Rohan Hule Jinkee Lee

Christopher MettingMaria Torija

Outline

• USANS• Problem background• Experimental design• Analysis• Results• Conclusions

USANS Capabilities

Graphite Filter

Sapphire Filter

Premonochromator

Monochromator

Monitor

Sample Changer

Main Detector

Analyzer

Transmission

Detector Isolation Table

Apertures

Scale: 1 m PCD Simplified Layout3.CV5

• Low q range– 3x10-5 Å-1 < q < 0.01 Å-1

• Particle Diameter: 0.1 μ m < D < 10 μm

Problem Background

• Fatigue causes voids in copper lattice

• Voids grow nucleate at grain boundaries

• Lead to mechanical failure

• Relationship between stress and void growth

Stress Axis

fatigue_cavity.CV5

Void

Grain Boundary (Diamond Configuration)

Experimental Design

• Fatigue conditions– 405 oC– 17 cycles/second– Max stress amplitude: 34 MPa

• Monitor void growth by varying the number of fatigue cycles– 25,000; 50,000; 100,000 cycles

• USANS to examine growth shape and size

Reduced Slit Smeared USANS DataSlope= -1 (plate)

Slope= -3 (Porod)

Porod Scattering, 100,000 cycles

0 100

1 10 -7

2 10 -7

3 10 -7

4 10 -7

5 10 -7

6 10 -7

7 10 -7

8 10 -7

0 100 5 10 -4 1 10 -3 1.5 10 -3 2 10 -3 2.5 10 -3

q•d

s/d

(q)

Å-1

cm-1

q (Å-1 )

blue_Porod.gra

3

Intercept ~surface area/sample volume-3

Invariant

0

0.5

1

1.5

2

2.5

3

3.5

4

0 100 5 10-4 1 10-3 1.5 10-3 2 10-3 2.5 10-3

q•d

/d

(q)

Å-1

cm-1

q (Å-1 )

blue_invariant.gra

Area under curve ~ Volume Fraction

Modified Guinier (plate)

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

0 100 5 10 -7 1 10 -6 1.5 10 -6 2 10 -6 2.5 10 -6 3 10 -6 3.5 10 -6 4 10 -6

ln(q

•d

s/d

(q))

Å-1

cm-1

q2 (Å-2 )

blue_mGuinier.gra

m= -T2/12

Results

Number of Cycles

  25,000 50,000 100,000

Surface area/Sample volume (cm2/cm3) 160 240

Volume fraction 5.80E-04 1.70E-03 2.90E-03

Average diameter (m) 0.60 0.72

Average volume (m3) 0.11 0.20

Number of voids/sample volume (cm-3) 1.50E+10 1.40E+10

Plate thickness (m) 0.36 0.55 0.63

Comparison with prior workScripta Met. 24 (1990) 227-232

Conclusions

• USANS proved to be a powerful tool for this investigation

• Average volume increases with cycle number

• Number of nucleation sites is independent of the number of cycles

HURRAY for USANS!

Thanks to John Barker, Man-Ho Kim, and David Mildner

Questions?

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