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Measurement of W - F82H Bond
Strength Using Laser Spallation Interferometer
Jaafar El-Awady, Hyoungil Kim, Jennifer Quan, Shahram Sharafat, Vijay Gupta, and Nasr Ghoniem
Mechanical and Aerospace Engineering Department University of California Los Angeles (UCLA)
Experimental Results
Introduction
• Tungsten is the primary candidate armor material protecting the low activation
ferritic steel first wall (FW) chamber.
• It is a required goal to determine the interface bond strength of W-armor/ferritic
steels as a function of vacuum plasma spraying (VPS) parameters as well as to
establish a lifetime for W-armor/steel interface bond as a function of number of
thermal cycles induced by (a) laser, and (b) x-rays simulated pulses, and (c)
RHEPP ion pulses: Develop low-cycle “SN curve” for W-armor delamination.
• Interface bond strength between tungsten and F82H has been quantified using
the laser spallation interferometer experiment in order to provide guidance for
further R&D of the W-armor protected FW.
• The tungsten/F82H sample was impinged at 6 different locations with 6
different laser fluence energies to determine the critical energy that would
result in failure of the W/F82H bond.
• The sample was cross-sectioned at the location of impingement to detect any
failure at the interface between the tungsten layer and the F82H layer.
• The following table shows the effect of increasing laser fluence on the failure
of the bond:
Laser
Fluence
613 mJ
Failure
No Failure
1065 mJ
1329 mJ
1577 mJ
1708 mJ
1737 mJ
No Failure
Some Crack
generating at
the interface
Severe
damage
Severe
Damage
Severe
Damage
• The following figures below are magnifications showing the failure at the
interface for different laser fluences.
100mm
Laser Fluence:
1577 mJ
Laser Fluence:
1329 mJ
W
The Laser Spallation
Interferometer Experiment
100mm
W
F82H
F82H
Crack
nucleation
• A 6-ns long Nd:YAG laser pulse is made to impinge over a f3mm area on a
0.5 mm thick aluminum film that is sandwiched between the back surface of a
substrate disk and a 10–20 mm thick layer of SiO2.
• The melting-induced expansion of the aluminum layer under confinement
generates a compressive stress pulse that propagates towards the bonding
interface.
• This compressive stress wave reflects as a tensile stress wave from the free
surface of the coating and cause tensile failure (spallation) at the
coating/substrate interface.
• This tensile stress, causing failure at the interface, is obtained by measuring
the transient displacement history of the coating’s free surface (induced during
pulse reflection) by using an optical interferometer (Pronin and Gupta, 1993).
Nd:YAG Laser
Continuum Corp.
Specimen
Holder
T
Model: Precision II
Energymeter
F82H
1064nm wavelength
F82H
Laser Fluence:
1708 mJ
He-Ne laser
Mirror
Interferometer
Coating
Aluminum
Substrate
Convex
Lens
Si
Mn
P
0.095
0.10
0.10
Ta
Ni
Mo
Ti
0.040
< 0.02
< 0.01
0.005
S
< 0.005 0.0030
B
Cr
W
V
7.72
1.95
0.018
SolAl
N
Nb
0.01
0.0001
0.00016 < 0.001
Tungsten:
W
F82H
F82H
Delemination
• The highest laser fluence energy that caused no failure, 1065 mJ, was
used to calculate an initial guess for the tensile strength of the bond.
• The velocity history of the coating’s free surface at this laser energy was
obtained by using an optical interferometer and is shown in the figure
below.
v(t )  C (e  e )
• The bond strength can
be obtained by
reading the velocity
history into a finite
element code
(ANSYS).
• The figure on the right give the stress
history at the interface for different
assumptions on the value of the elastic
modulus of the tungsten layer.
The tungsten layer is assumed to be
softer than that of single crystal tungsten.
• From the Analysis it can be estimated
that the bond strength will greatly depend
on the elastic modulus of the coating. It will
fall in the range
300MPa   c  1050MPa
•HAPL-Rochester, NY Nov. 8-9
C
HIP Condition
W
The Velocity Profile:
t / A
SiO2
The chemical composition in mass% of the F82H is shown in the following
table:
100mm
The measured fringe record:
Beam
Splitter for
Nd:YAG
• A rod f28mm x 30mm was mechanically cut out from a a 32mm thick
plate.
• The bonding interface was polished by 0.03mm silicon carbide powder
and finally degreased by acetone.
F82H
Interface Strength Measurement
6ns-duration
CT CR
W
Crack
nucleation
F82H:
• The starting material was heat treated first at 1313K for a duration of 40
minutes for normalizing and then at 1023K for a duration of 60 minutes
for tempering.
• A tungsten disk f20mm x 0.05mm was mechanically cut out from a rod
f28mm x 100mm by electrical discharge machining.
• The tungsten purity was 99.95% and the disk was degreased by acetone.
W
W
Specimen Materials Description
Pretreatment:
• The was encapsulated to SUS304 capsule which has degassing pipe.
The capsule was heated up to 1373K for 1hour. The vacuum level inside
the capsule was 5x10-4Pa. After the degassing, the degassing pipe was
enclosed by TIG welding.
HIP operation:
• F82H joint was fabricated with
HIP conditions of 1243K, 143MPa and
2hour houldingtime. The temperature
and pressure history is shown
in the adjacent figure:
t / B
Sample Specimen:
W coating
D = 20 mm
1.1 mm
50 mm
F82H substrate
F82H substrate
W coating