Laser Ultrasonic Testing for Estimation of Adhesion of Al₂O₃ Plasma Sprayed Coatings

Abstract

The aim of the present study was to investigate the possibility of using a laser ultrasonic technique for the estimation of the adhesion of ceramic coatings, deposited onto metallic substrates by thermal spraying techniques. For this purpose, a pulsed Nd : YAG laser (λ = 1064 nm, 14 ns) was used to irradiate Al2O3 coatings, of different thickness (30–350 µm), deposited onto stainless steel substrates by atmospheric plasma spraying. The laser generated ultrasonic waves were in situ recorded at the epicentre using a laser heterodyne interferometer. The acoustic waveforms were correlated with the interaction between the pulsed laser radiation and the coated metal, taking into account the physical properties and the geometry of both the coating and the substrate, as well as the porosity of the coating. For the critical value of laser beam energy for which debonding just occurred, the stress field, owing to the combined thermal and acoustic effects of laser radiation, was calculated. The obtained values of the stress intensity factor KIC and the strain energy release rate GIC were correlated with previous relative data concerning the three-point bending test, and were found to be in very good agreement, demonstrating the potential of the proposed technique for the estimation of the adhesion strength of transparent ceramic coatings deposited on metallic substrates by thermal spraying techniques.

Measurement of fracture toughness and interfacial shear strength of hard and brittle Cr coating on ductile steel substrate

“…The chromium coatings, composed of low contraction (LC) and high contraction (HC) chromium, were prepared by the commercial electroplating of practical chromium coated parts. The LC Cr layer y20 mm thick was predeposited as an interlayer with the commercial plating bath of chromic acid (250 g L 21 ) and sulphuric acid (2?5 g L 21 ), at a temperature of 85uC and a current density of 60 A dm 22 . The HC Cr plate approximately 80 mm thick was deposited at a lower bath temperature and a lower current density.…”

“…The higher fracture toughness means a higher crack propagation resistance, and the higher interfacial shear adhesive strength means a higher crack initiation resistance during the shear stress loading. Various experimental methods such as the pull-off test, 10,11 scratch test, [12][13][14][15] indentation test, [14][15][16][17][18][19] impact test 20,21 and laser ultrasonic testing method 22,23 have been used to evaluate the coating fracture properties and interfacial adhesion properties between the coating and the substrate. However, the methods mentioned above for adhesion measurement have limitations.…”

In-Situ Simultaneous Measurement of Thickness, Elastic Moduli and Density of Thermal Sprayed WC-Co Coatings by Laser-Ultrasonics

“…Previous works on ultrasound for the characterization of thermal sprayed coatings have shown the great potential of the technique to measure various properties like elastic constants (Ref [1][2][3][4][5][6][7][8], thickness (Ref 1,4) and adhesion (Ref 5,9,10). The ultrasonic waves propagate through the thickness of the coating (bulk waves) or along the coating (surface waves).…”

Elastic Modulus Measurements via Laser-Ultrasonic and Knoop Indentation Techniques in Thermally Sprayed Coatings

“…One of the most promising techniques is laser-ultrasonics. Some refereed studies are available in the literature (Ref [15][16][17][18][19][20].…”

“…Despite the publication of various refereed studies in the coatings literature on laser-ultrasonics and E measurements (Ref [15][16][17][18][19], this method is not very well known and is little used by the thermal spray community. One of the reasons for this is, as already discussed, the highly anisotropic and inhomogeneous structure of these coatings, consisting of intersplat pores and cracks (Ref 2-10).…”