THERMAL SPRAY DIAGNOSTICS - Part I - What's Out There?

As anyone who has dealt with thermal spray technology knows, there is more to spraying quality coatings than just purchasing a functional spray system and reading an operation manual.  In many cases, attaining the proper spray parameters to meet coating specifications in a safe and profitable manner is not trivial.  Even with an experienced operator and a well maintained thermal spray system, variations in coating quality is not too uncommon.  In recent years, the advancements in diagnostic tools, specifically for thermal spray, have made beneficial contributions towards optimization of spray parameters and trouble-shooting of coating quality deviations.  In addition, user-friendly in-flight process diagnostic tools have improved the understanding of thermal spray processes from a trial-and-error approach to a more scientific one.

Although most of the existing thermal spray diagnostic tools are used by scientists, more and more are being introduced to the production floor, especially for applications that require a very high degree of consistency, i.e., coatings for gas turbine engine components.  A quick search in open literature on diagnostic tools provided some insight into types and models of sensors used to determine in-flight particle temperature and velocity.  Twenty-one arbitrarily selected publications ^[i-xxi] that incorporated the use of thermal spray diagnostic tools led to the following:

• Over 85% of the authors/co-authors were from academia or research centers
• All of the publications focused on using diagnostic tools to determine in-flight particle temperature and velocity
• Just over half of the publications used the DPV 2000 (Tecnar Automation Ltd., Quebec, Canada) diagnostic sensor alone or in combination with other sensors
• Since 2006, 60% of the publications used the Accuraspray (Tecnar Automation Ltd., Quebec, Canada) diagnostic sensor alone or in combination with other sensors
• The diagnostic tools were used to monitor mainly APS and HVOF processes, with a couple for TWAS
• Majority of the feedstock monitored were ceramics (~ 61 %), then metals (~ 26 %), and finally carbide cermets (~ 13 %)

Simple to setup and robust sensor monitoring with a reliable real-time feedback control system seems to be something of the near future and will take even more of the remaining art out of thermal spray. 

REFERENCES

i.      W. Zhang, S. Sampath, “A Universal Method for Representation of In-Flight Particle Characteristics in Thermal Spray Processes”, Journal of Thermal Spray Technology Volume 18(1) March 2009, pp. 23-34Peer

ii.     E. Turunen, A. Hirvonen, T. Varis, T. Fält, S.-P. Hannula, T. Sekino, K. Niihara, Application of HVOF Techniques for Spraying of Ceramic Coatings”, Journal of Materials Online, Dec. 2007, Vol. 3

iii.   S.P. Mates, D. Basak, F.S. Biancaniello, S.D. Ridder, J. Geist, “Calibration of a Two-Color Imaging Pyrometer and Its Use for Particle Measurements in Controlled Air Plasma Spray Experiments”, Journal of Thermal Spray Technology Volume 11(2) June 2002, pp. 195-205viewed

iv.   E. Turunen “Diagnostic tools for HVOF process optimization”, Espoo 2005. VTT Publications 583. 66 p. + app. 92 p.

v.     J.R. Fincke, W.D. Swank, R.L. Bewley, D.C. Haggard, M. Gevelber, D. Wroblewski, “Diagnostics and control in the thermal spray process”, Surface and Coatings Technology 146 –147 (2001) pp. 537–543

vi.   T. Patterson, “Diagnostics Correlation Study of 8%-YSZ Deposited by F4-MB APS Torch”, UTSR Report 2006, http://www.clemson.edu/scies/UTSR/FellowPattersonSUM6.pdf

vii.  C. Moreau, J.-F. Bisson, R. S. Lima, B. R. Marple, “Diagnostics for advanced materials processing by plasma spraying”, Pure Appl. Chem., Vol. 77, No. 2, pp. 443–462, 2005

viii.         M. Li, D. Shi, P.D. Christofides, “Diamond Jet Hybrid HVOF Thermal Spray: Gas-Phase and Particle Behavior Modeling and Feedback Control Design”, Ind. Eng. Chem. Res. 2004, 43, pp. 3632-3652

ix.   M. Cherigui, Z. Salhi, N.E. Fenineche, P. Gougeon, C. Coddet, “FeSi HVOF thermal spray coatings: diagnostic, microstructure, and magnetic properties” Materials Letters 59 (2005) pp. 463– 467

x.     F.D. Witherspoon, D.W. Massey, R.W. Kincaid, G.C. Whichard,  T.A. Mozhi, “High Velocity Pulsed Plasma Thermal Spray”, Journal of Thermal Spray Technology Volume 11(1) March 2002, pp. 119-128

xi.   Gary S. Settles and Sarah R. Bekofske, “HVOF THERMAL SPRAY VELOCITY, TEMPERATURE, AND STAINLESS STEEL COATING PROPERTIES”, Sixteenth Symposium on Energy Engineering Sciences, May 13-15, 1998, pp. 187-194

George E. Kim, Ph.D.

F.W. Gartner

Perpetual Technologies, Inc.

email: gkim@perpetualtech.ca

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