• 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:

• The following figures below are magnifications showing the failure at the interface for different laser fluences.

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)

Measurement of W - F82H Bond Strength Using Laser Spallation Interferometer

IntroductionIntroduction• 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 Laser Spallation The Laser Spallation Interferometer ExperimentInterferometer Experiment

• A 6-ns long Nd:YAG laser pulse is made to impinge over a 3mm area on a 0.5 m thick aluminum film that is sandwiched between the back surface of a substrate disk and a 10–20 m 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).

CT CR

T

6ns-duration

Beam Splitter for Nd:YAG

Energymeter

Mirror

Convex Lens

Specimen Holder

SiO2

Substrate

Coating

He-Ne laser

Interferometer

Aluminum

Nd:YAG Laser

Continuum Corp.

Model: Precision II

1064nm wavelength

Experimental ResultsExperimental Results

Laser Fluence

613 mJ 1065 mJ 1329 mJ 1577 mJ 1708 mJ 1737 mJ

Failure No Failure No FailureSome Crack generating at the interface

Severe damage

Severe Damage

Severe Damage

• 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.

• The bond strength can be obtained byreading the velocityhistory into a finite element code (ANSYS).

• The figure on the right give the stresshistory at the interface for different assumptions on the value of the elasticmodulus 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 willfall in the range

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 rod 28mm x 30mm was mechanically cut out from a a 32mm thick plate.

• The bonding interface was polished by 0.03m silicon carbide powder and finally degreased by acetone.

The chemical composition in mass% of the F82H is shown in the following table:

Tungsten:

• A tungsten disk 20mm x 0.05mm was mechanically cut out from a rod 28mm x 100mm by electrical discharge machining.

• The tungsten purity was 99.95% and the disk was degreased by acetone.

Specimen Materials DescriptionSpecimen Materials Description

C Si Mn P S Cr W V

0.095 0.10 0.10 < 0.005 0.0030 7.72 1.95 0.018

Ta Ni Mo Ti B SolAl N Nb

0.040 < 0.02 < 0.01 0.005 0.00016 < 0.001 0.01 0.0001

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 temperatureand pressure history is shown in the adjacent figure:

Sample Specimen:

50 m

W coating

F82H substrate

1.1 mm

W coatingF82H substrate

D = 20 mm

HIP ConditionHIP Condition

100m

F82H

W

Laser Fluence: 1577 mJ

100m

F82H

W

Laser Fluence: 1329 mJ

W

F82H

100m

F82H

W

F82H

W

Laser Fluence: 1708 mJ

W

F82H

F82H

W

Delemination

Crack nucleation

Crack nucleation

Interface Strength MeasurementInterface Strength Measurement

)()( // BtAt eeCtv

The measured fringe record: The Velocity Profile:

MPaMPa c 1050300

•HAPL-Rochester, NY Nov. 8-9