Residual Stress Measurement of Suspension HVOF-Sprayed Alumina Coating via a Hole-Drilling Method
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Residual Stress Measurement of Suspension HVOF-Sprayed Alumina Coating via a Hole-Drilling Method T. A. Owoseni1 • M. Bai2 • N. Curry3 • E. H. Lester1 • D. M. Grant1 T. Hussain1
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Submitted: 2 October 2019 / in revised form: 1 June 2020 Ó The Author(s) 2020
Abstract The nature and magnitude of residual stresses in thermal-sprayed coatings determine their lifetime and failure mechanisms. The residual stresses of suspension high-velocity oxy-fuel (SHVOF) thermal sprayed alumina (Al2O3) coating were measured with hole-drilling and x-ray diffraction. The coating is dense and consists of amorphous and two crystalline phases: alpha and gamma. The residual stresses measured by hole-drilling in the Al2O3 coating was - 162 MPa (compression) in the longitudinal direction and - 104 MPa (compression) in the transverse direction. This is due to the peening stress and the high substrate–coating CTE ratio of * 2.1. The nature of the residual stress through the coating is related to the microstructure build-up shown from the cross section and the fracture surfaces of the coating. Keywords alumina hole-drilling residual stress SHVOF thermal-spray coating
Residual Stresses Credit Line: This article is part of a special topical focus in the Journal of Thermal Spray Technology on Advanced Residual Stress Analysis in Thermal Spray and Cold Spray Processes. This issue was organized by Dr. Vladimir Luzin, Australian Centre for Neutron Scattering; Dr. Seiji Kuroda, National Institute of Materials Science; Dr. Shuo Yin, Trinity College Dublin; and Dr. Andrew Ang, Swinburne University of Technology. & T. Hussain [email protected] 1
Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK
2
Department of Materials Science and Engineering, University of Sheffield, Sheffield, South Yorkshire, UK
3
Treibacher Industrie AG, Auer-von-Welsbach-Straße 1, 9330 Althofen, Austria
Introduction Thermal spray is a widely used surface engineering process for coating deposition, which involves propelling melted or partially melted particles onto the surface. Thermal spray coatings can be deposited from most materials: primarily from rod, wire or powder fed into a plasma or a combustion gas as in a flame spray of a high-velocity oxy-fuel (HVOF) thermal spray (Ref 1). Thermal spray is used in depositing ceramic materials for high value engineering applications, for example, Al2O3 coatings in electrical insulation, corrosion, and wear applications (Ref 2-4). Suspension spray is a relatively new branch of thermal spray where instead of a dry powder feedstock, suspensions are used. Suspensions are fed into plasma as in suspension plasma spray (SPS) (Ref 5) or into combustion gas in the case of suspension high-velocity oxy-fuel (SHVOF) spray (Ref 6)—both SPS and SHVOF can deposit coatings from sub-micron- to nanometric-size feedstock carried in liquid media. The overall performance and lifetime of coatings are subject to the magnitude and nature of their residual stresses (Ref 7). The nature of the r
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