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Journal of Thermal Spray Technology

, Volume 20, Issue 5, pp 1071–1084 | Cite as

AE Monitoring and Analysis of HVOF Thermal Spraying Process

  • N. H. Faisal
  • R. AhmedEmail author
  • R. L. Reuben
  • B. Allcock
Peer Reviewed

Abstract

This work presents an in situ monitoring of HVOF thermal spraying process through an acoustic emission (AE) technique in an industrial coating chamber. Single layer thermal spraying on substrate was carried out through slits. Continuous multilayer thermal spraying onto the sample without slit was also conducted. The AE was measured using a broadband piezoelectric AE sensor positioned on the back of the substrate. A mathematical model has been developed to determine the total kinetic energy of particles impacting the substrate through slits. Results of this work demonstrate that AE associated with particle impacts can be used for in situ monitoring of coating process. Results also show that the amplitude and AE energy is related to the spray gun transverse speed and the oxy-fuel pressure. The measured AE energy was found to vary with the number of particles impacting the substrate, determined using the mathematical model.

Keywords

acoustic emission HVOF monitoring multilayer spraying non-destructive testing particle impact thermal spray 

Nomenclatures

A

Spray spot area

As (t)

Trigonometric spray spot area function of time

E

Acoustic emission energy

\( \dot{E}(t) \)

Kinetic energy of powder particles as a function of time

Ec

Deposit stiffness

mp

Mass of one powder particle

\( \dot{m} \)

Mass flow rate of powder particle impinging on the target

\( \dot{m}_{\text{powder}} \)

Powder particle mass flow rate

\( \dot{N} \)

Number of particles approaching the slit per second

\( \dot{N}_{\text{S}} (t) \)

Number of particles approaching the slit as a function of time

r

Powder particle radius

R

Spray spot radius

Rdc

Ring-down count

t

Time

T

Slit passing (scanning) time

Te

Event duration

Tθ

Time (for angle of arc subtended at the slit Edge 1)

Tm

Lamella melting temperature

TS

Substrate temperature

V

Average powder particle speed

Vg

Lateral speed of HVOF spraying gun

Vabs

Absolute voltage

Vt

Threshold voltage

y

Slit width

z

Center of slit

Greek Symbols

θ(t)

Angle of arc subtended at the slit Edge 1 as a function of time

δ(t)

Angle of arc subtended at the slit Edge 2 as a function of time

ρ

Density of powder particle

σq

Quenching stress

αc

Deposit coefficient of thermal expansion

Subscripts

abs

Absolute

c

Coating deposit

dc

Ring-down count

e

Event

g

HVOF gun

m

Lamella melting

p

Powder particle

q

Quenching

s

Slit

S

Coating substrate

t

Threshold

Abbreviations

ADC

Analog-to-digital converter

AE

Acoustic emission

CNC

Computer numerical control

DAQ

Data acquisition card

HVOF

High-velocity oxygen fuel

IIR

Infinite impulse response

PAC

Physical Acoustics Corporation

PZT

Lead zirconate titanate

RMS

Root mean square

SCU

Signal conditioning unit

SEM

Scanning electron microscopy

SNR

Signal-to-noise ratio

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Copyright information

© ASM International 2011

Authors and Affiliations

  • N. H. Faisal
    • 1
    • 2
  • R. Ahmed
    • 1
    • 2
    Email author
  • R. L. Reuben
    • 1
  • B. Allcock
    • 3
  1. 1.Department of Mechanical Engineering, School of Engineering and Physical SciencesHeriot-Watt UniversityEdinburghUK
  2. 2.College of EngineeringAlfaisal UniversityRiyadhKingdom of Saudi Arabia
  3. 3.Monitor Coatings Ltd, Monitor HouseTyne & WearUK

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