Application of acoustic emission for monitoring Application of acoustic emission for monitoring the HVOF thermal spraying processthe HVOF thermal spraying process

N. H. Faisal, J. A. Steel, R. Ahmed, R. L. Reuben, G. HeatonDept. ofMechanical Engineering, Heriot-Watt UniversityDept. ofMechanical Engineering, Heriot-Watt University

Edinburgh, UK, Email: N.H.Faisal@gmail.com

B. AllcockMonitor Coatings Ltd.

Tyne & Wear, UK

27th European Working Group on Acoustic Emission (EWGAE) 21st September 2006, Cardiff, UK

Presentation StructurePresentation Structure•• IntroductionIntroduction

–– What is HVOF Thermal Spray Coatings / Applications?What is HVOF Thermal Spray Coatings / Applications?–– Why AE Monitoring during Thermal Spraying?Why AE Monitoring during Thermal Spraying?–– Quality Control issues in Thermal Spray CoatingsQuality Control issues in Thermal Spray Coatings

•• Experimental Systems and TechniquesExperimental Systems and Techniques

•• ResultsResults–– AE Signal CharacteristicsAE Signal Characteristics–– Development of Kinematic Model of Particle ImpactDevelopment of Kinematic Model of Particle Impact

Bio-medical/Knee, Hip, Elbow joints

Aerospace/Turbine

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Bio-medical/Knee, Hip, Elbow

–– Development of Kinematic Model of Particle ImpactDevelopment of Kinematic Model of Particle Impact–– Influence of Continuous MultiInfluence of Continuous Multi--layer Thermal Sprayinglayer Thermal Spraying

•• Summary, Conclusions and Future WorkSummary, Conclusions and Future WorkElectronics/Heat sink

Thermal Spray: Industries / ApplicationsThermal Spray: Industries / Applications

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HVOF Spray gun Plasma Spray gun

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tings.co.u

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HVOF Thermal Spray (TS) CoatingsHVOF Thermal Spray (TS) CoatingsWhat is HVOF (High Velocity Oxygen-Fuel) Thermal Spraying process

Coating substrate

HVOF Thermal Spraying system

Splat cooling rate: 100-600K/µs

Powders velocity: 600-800m/s

Flame tempe: 3000-5000˚C

Gas velocity: 1500-2000m/s

Particle Temp: 1500-2000˚C

TAFA JP-5000Monitor Coatings Ltd. UK

HVOF Coating chamber

Spray spot ~ 9-12mm

HVOF nozzle/gun

Sources of AE:Sources of AE:

AE monitoring system

Single WC-10Co-4Cr particle splat

WC-10Co-4Cr Powders

After spraying/Partially melted

Noise level in coating chamber ~ 123dB ~ Jet-Engine take-off noise

Sources of AE:Sources of AE:•• Particle impact Particle impact (Kinetic energy / Strain energy released)(Kinetic energy / Strain energy released)

•• Thermal mismatch, Cracks in layersThermal mismatch, Cracks in layers•• Coating chamber reverberation (noise)Coating chamber reverberation (noise)

Why AE monitoring during TS?Why AE monitoring during TS?•• It addresses core technological issues:It addresses core technological issues:

Quantifies the partially melted powder particle Quantifies the partially melted powder particle landing behaviour & phase changes during landing behaviour & phase changes during spraying & cooling process spraying & cooling process ––Fundamental to Fundamental to coatings strength determination coatings strength determination

•• Monitors Monitors quality during the coating formation quality during the coating formation •• Added Added advantageadvantageover existing quality control over existing quality control

techniquestechniques

Existing OffExisting Off--line Techniques line Techniques ((postpost--spraying processspraying process))

e.g., Mechanical Testing procedures: It Requires‘TEST COUPONS’ (e.g. for Bending, Indentation, Tensile, Adhesion, Fatigue, Wear, Thermal Cycling tests)

Existing OnExisting On--line Techniques (line Techniques (postpost--spraying processspraying process))

e.g., Non-Destructive Testing procedures: Ultrasonic,

Quality Control issues in TS CoatingsQuality Control issues in TS Coatings

Bending test

There is no ‘on-line’ coatings quality monitoring (i.e., DURINGSPRAYING) available which can quantify the splat landingbehaviour and which can measure the cohesive & adhesivestrengths on ACTUAL COMPONENTS

e.g., Non-Destructive Testing procedures: Ultrasonic, Radiographic, Electromagnetic, Liquid penetrant, Magnetic particle, 4-point bending test + AE, Indentation test + AE

Thermal Spraying / AE measurementThermal Spraying / AE measurement

Pre-amplifier: PAC-1220APre-amp at 40/60 dB,Gain at SCU = 0 dB

PAC, Micro-80D: Broadband PZT sensor (0.1-1.0 MHz), Rf = 332kHz

12 bit NI, PCI-6115 DAQ, and AE 4-channel system; Sampling rate

2.5MHz/2 sec

CPU, Computer & AE system

HVOF SystemTAFA

JP-5000

Slit/mask

HVOF nozzle/gun

(A) Using

slit

(B)

Coating chamber

SubstrateHolder

HVOF System, Coating chamberCoating substrateMasking-sheet (slits)Masking-sheet/Substrate

set-upMasking-sheet-substrate-

sample holder set-up

Without slit

Experimental matrix & MaskingExperimental matrix & Masking--sheet (slit)sheet (slit)

HVOF Thermal

Spray Parameters

Pressure level-P1 Pressure level-P2

O/F ratio = 1.16 (P1); Oxygen flow rate, 1950scfh; Powder feed gas, Nitrogen (21 scfh); Fuelflow rate, 6 gallon/min (kerosene); Powder feedrate, 80 g/min

O/F ratio = 1.21 (P2); Oxygen flow rate, 1950scfh; Powder feed gas, Nitrogen (21 scfh);Fuel flow rate, 4.5 gallon/min (kerosene);Powder feed rate, 80 g/min

Slit no. and width

A(3mm)

B(2mm)

C(1mm)

D(0.5mm)

A(3mm)

B(2mm)

C(1mm)

D(0.5mm)

Gun scanning

speed (mm/sec.)

250 1 1 1 1 1 1 1 1

A: 3 mm

27 mm

Gun motion Coating Substrate (Mild-Steel)

Masking-sheet (Mild-Steel)

250 1 1 1 1 1 1 1 1

500 1 1 1 1 1 1 1 1

750 1 1 1 1 1 1 1 1

1000 1 -- -- -- 1 -- -- --

10m

m

AE Signal Characteristics (Background noise)I. AE signal during flame spraying only beside slit-substrate without powder

II. AE signal during flame and powder spraying beside slit-substrate

Masking-sheet (slits)

Coating substrate

Coating substrate

0 0.5 1 1.5 2-0.2

-0.1

0

0.1

0.2

Time (s)

Am

plitu

re (

V)

nopowderbesidesample010000.bin

0.2powderbesidesample010000.bin

0 5 10 15

x 105

0

2

4

6

8x 10

-8 Frequency domain: no powder beside sample010000.bin

Frequency (Hz)

Pow

er s

pect

ral d

ensi

ty

4x 10

-8 Frequency domain: powder beside sample010000.bin

Coating chamber Noise level

5, 50, 100, 140kHz

5, 50, 100, 140kHz

III. AE signal during flame spraying only on substrate without powder

Coating substrate

Masking-sheet (slits)0 0.5 1 1.5 2

-0.2

-0.1

0

0.1

Time (s)

Am

plitu

re (

V)

0 0.5 1 1.5 2-0.2

-0.1

0

0.1

0.2

Time (s)

Am

plitu

re (

V)

flamepass010000.bin

0 5 10 15

x 105

0

1

2

3

Frequency (Hz)

Pow

er s

pect

ral d

ensi

ty

0 5 10 15

x 105

0

1

2

3

4x 10

-8 Frequency domain: flame pass010000.bin

Frequency (Hz)

Pow

er s

pect

ral d

ensi

ty

5, 50, 100, 140kHz

5, 50, 100, 140kHz

Coating chamber Noise level

Coating chamber Noise level

IV. AE signal during full spraying (both flame and powder) at standard spraying pressure P-1

AE Signal Characteristics

Masking-sheet (slit A), 3mm width, 10mm height

Substrate: Coatings through slit-A

Gun speed: 500mm/sec

500mm

No. of Slits: 14

1.5x 10

-7 Frequency domain: hvof12010000.bin

5-100kHz (BNG)SNR ~ 3 to 4

0 5 10 15

x 105

0

0.5

1

1.5

Frequency (Hz)

Pow

er s

pect

ral d

ensi

ty

5-100kHz (BNG)100-200kHz300-400kHz550-650kHz750-850kHz

BGN

Development of Kinematic Model Development of Kinematic Model (particle impact)(particle impact)

Phase difference & Area distribution (3mm slit, 250mm/sec)

10

20

30

40

50

60

70

Are

a [m

m^2

]

area(theta)

area(delta)

effective area

Effective Spraying Area = (1/2) . [R2 {2 (θ-δ) - (Sin 2θ-Sin 2δ)}] = Curve3Gun Speed, Vg

D’D

Slit width, y

D’D

Curve2 (Edge-2)

Curve1 (Edge-1)

Curve3 = [Curve1-Curve2]

Slit centre

x1x1 x2x2

EdgeEdge--11 EdgeEdge--22

0

0 0.01 0.02 0.03 0.04 0.05 0.06

Time [sec]

Slit centre

Area distribution (3mm slit, 250mm/sec gun speed)

0

10

20

30

40

50

0 0.01 0.02 0.03 0.04 0.05 0.06

time [sec]

Are

a

area

x1x1 x2x2

x1x1 x2x2

Curve3 = effective spraying area

Kinematic Model of Particle ImpactKinematic Model of Particle Impact

(a) (b) (c)

Time length = 0.052sec

-0.5

0

0.5

1

Am

plitu

re (

V)

hvof11010000.binK.E of powder particles making impact through effective area is, E = [(1/2).M.V.V];

E = (1/2) . [N. mp].(R.R/2). [2 (θ-δ) – (Sin 2θ-Sin 2δ)] .V.Vwhere V is the velocity of sprayed particle

SNR ~ 3 to 4

100150200250300350400450

Th

eore

tica

l en

erg

y [k

g.m

^2/

s^2]

per

slit

Slit-A: 3mm Slit-B: 2mm Slit-C: 1mm Slit-D: 0.5mm

1000

2000

3000

4000

5000

6000

Exp

erim

enta

l AE

en

erg

y [V

.s]

per

slit

Slit-A: 3mm Slit-B: 2mm Slit-C: 1mm Slit-D: 0.5mm

Experimental Area Theoretical Area

0.00 0.01 0.02 0.03 0.04 0.05 0.060

5000

10000

15000

20000

Th

eore

tica

l

Kin

etic

En

erg

y d

istr

ibu

tio

n [

Kg

.m2 .s

-2]

Time of spray gun transversing the slit [seconds]

KE (Slit width: 3mm; Gun Speed: 250mm/sec )

0.05 0.1 0.15

-0.4

-0.2

0

0.2

0.4

0.6

Time (s)

Am

plitu

re (

V)

0 0.5 1 1.5 2-1

-0.5

Time (s)

3mm slit width, 250mm/sec gun speed0 250 500 750 1000

050

Th

eore

tica

l en

erg

y [k

g.m

^2/s

^2]

HVOF gun transverse speed [mm/sec]

0 250 500 750 10000

1000

Exp

erim

enta

l

HVOF gun transverse speed [mm/sec]

Experimental Theoretical

Smoothed signal

AE Monitoring During Multilayer Thermal AE Monitoring During Multilayer Thermal Spraying (without masking slit)Spraying (without masking slit) Coating builds-up

(cross-section)

Centre-line

Theoretical spray-spot ~ 9-12mm

Actual

Transverse Gun Speed

AE system

ww

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Actual spray-spot ~ 18mm

Actual spray-spot is greater than theoretical spray-spot due to fanning of spray

Influence of Continuous Multilayer Influence of Continuous Multilayer Thermal SprayingThermal Spraying

0.00002

0.00004

0.00006

0.00008

0.00010

0.00012

0.00014

0.00016

AE

en

erg

y (a

.u.)

per

un

it t

ime AE energy (a.u.)

Gun Speed200mm/sec

AE sensor location (centre-backside)

Layers1 2 3 4 5

AE sensor location

0 50 100 150 200 250 3000.00000

0.00002AE

en

erg

y (a

.u.)

per

un

it t

ime

No. of data files [time for 1 data file = 0.004 sec]

0 1 2 3

x 106

0

1

2

3

4

5x 10-7 Frequency domain: A1010000.sgl

Frequency (Hz)

Pow

er s

pect

ral d

ensi

ty

0 1 2 3 4

x 10-3

-1

-0.5

0

0.5

1

Time (s)

Am

plitu

re (

V)

A1010000.sgl

Chamber Noise ~ 0.15V

0 1 2 3 4

x 10-3

-1

-0.5

0

0.5

1

Time (s)

Am

plitu

re (

V)

A1010025.sgl

0 1 2 3

x 106

0

2

4

6x 10-7 Frequency domain: A1010025.sgl

Frequency (Hz)

Pow

er s

pect

ral d

ensi

tySNR ~ 4 Frequency340, 590 & 800kHz

Layers1 2 3 4 5

Summary

SprAE Monitoring Block DiagramSprAE Monitoring Block Diagram(Open loop system)(Open loop system)

Thermal Spray particle impact

Multilayer Spraying Spraying through slits

AE SignalAE SignalThermal Spraying system AE Signal

AE Energy distribution

Thermal SprayProcess Parameter

Monitoring

Amplitude, Frequency,Event (N), Energy (E),

Event duration (T)Event rate (N/T), Energy rate (E/T)

Thermal Spraying system

SprAE monitoring system

ConclusionsConclusions

•• AE monitoring system developed; High AE monitoring system developed; High SignalSignal--toto--Noise Ratio (3Noise Ratio (3--4)4)has has been measured during HVOFbeen measured during HVOF

•• As gun speed increases values of As gun speed increases values of AE parameters fall AE parameters fall through slitsthrough slits

•• AE energy increasesAE energy increasesas the number of layers increaseas the number of layers increase

•• Kinematic model has been developedKinematic model has been developed

•••• Other techniques: Other techniques: PlasmaPlasma, , DetonationDetonationand and Cold spray coating / AECold spray coating / AE

•• Future experimentation Future experimentation (DOE / Taguchi’s technique) / (DOE / Taguchi’s technique) / AEAE

•• Development of post spraying AE testsDevelopment of post spraying AE tests/ Identifying coating / Identifying coating strengthsstrengths

•• Development of Control processDevelopment of Control processduring Thermal Spraying / during Thermal Spraying / AEAE

•• Computational fluid dynamics (CFD)Computational fluid dynamics (CFD) analysis / AE signal analysis / AE signal distributiondistribution

•• Thermal Spray NThermal Spray Nozzle wear rate monitoringozzle wear rate monitoringusing AEusing AE

Future workFuture workThermal Spraying system

SprAE monitoring system

SprAE control system

Close loop system

?

Thanks!Thanks!Tyne & Wear Castle Edinburgh Castle

Any Questions Please?Any Questions Please?

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