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4909 |
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Wednesday, May 11, 2016, Room 3E 2:40 PM Suspension Spraying II |
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Tribology and nano-indentation study of suspension HVOF thermal sprayed alumina coatings |
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Tanvir Hussain* / University of Nottingham, Great Britain Eleanor Shaw / University of Nottingham, United Kingdom Andrew Siao Ming Ang/ Swinburne University of Technology, Australia Zdenek Pala/ University of Nottingham , UK Fang Xu/ University of Nottingham , UK |
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The suspension high velocity oxy fuel spraying of alumina has attracted much attention in the recent years for various tribology applications. The coatings processed via this route shows unique microstructural features and the thickness of the coatings can be tailored to bridge the gap between the traditional thin film (~1-2 um) and the conventional HVOF thermal sprayed coatings (~200 um). In this study, a water based alpha alumina suspension was used to deposit ~ 50 um thick coatings onto carbon steel substrates. The aim was to develop thin coatings with superior wear resistant properties. Hydrogen was used as a fuel gas and the effect of various processing parameters on the coating properties was examined. The coating microstructure was examined in a high resolution ESEM with EDX to identify the degree of particle melting and particle morphology. XRD was used as the primary route to study the phase transformation of the feedstock suspension. At higher combustion flame energy the coatings transformed entirely of gamma alumina and at lower flame energy the coatings were composed of a mixture of alpha and gamma alumina. Alpha to gamma transition was less sensitive to the changes in the standoff distance during spraying. The nanoindention technique has been applied to measure the hardness and elastic modulus of coatings from the load displacement curves. The nanoindentation tests, essentially, measured the sub-micrometre scale properties of the suspension HVOF sprayed alumina coatings, which are considered as near-intrinsic properties. The ball-on-plate wear tests were performed to investigate the relationship between the wear performance and the alpha/ gamma ratios in the coatings. |