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1335 |
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Wednesday, June 04, 2008, Room 04 9:40 AM HVOF and Flame Spraying New very hard coatings and modern powder feeding for economic dense coatings against wear and corrosion |
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Designing of an integrated semi automated powder feed device to produce functionally graded materials (FGM) using the HVOF thermal spray process |
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Joseph Stokes* / School of Mechanical & Manufacturing Engineering, National Centre for Plasma Science and Technology, Dublin City University, Ireland Kabir Al Mamun / Materials Processing Research Centre, Dublin City University & National Centre for Plasma Science & Technology, Dublin City University, Ireland Mahbub Hasan/ Materials Processing Research Centre, Dublin City University & National Centre for Plasma Science & Technology, Dublin City University, Ireland Lisa Looney/ Materials Processing Research Centre, Dublin City University & National Centre for Plasma Science & Technology, Dublin City University, Ireland Saleem Hashmi/ Materials Processing Research Centre, Dublin City University & National Centre for Plasma Science & Technology, Dublin City University, Ireland |
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The application of FGMs is quite difficult, but thermal spray processes like Plasma spray have demonstrated their unique potential in producing graded deposits, where researchers have used twin powder feed systems to mix different proportions of powders. FGMs vary in composition and/or microstructure from one boundary (substrate) to another (top service surface), and innovative characteristics result from the gradient from metals to ceramics or non-metallic to metals. The present study investigates an innovative modification of a HVOF (High Velocity Oxy-Fuel) thermal spray process to produce functionally graded thick coatings. In order to deposit thick coatings, certain problems have to be overcome. Graded coatings enable gradual variation of the coating composition and/or microstructure, which offers the possibility of reducing residual stress build-up with in coatings. In order to spray such a coating, modification to a commercial powder feed hopper was required to enable it to deposit two powders simultaneously which allows deposition of different layers of coating with changing chemical compositions, without interruption to the spraying process. Various concepts for this modification were identified and one design was selected, having been validated through use of a process model, developed using ANSYS Flotran Finite Element Analysis. In the current research the mixing of different proportions of powders were controlled by a computer using LabVIEW software and hardware, which allowed the control and repeatability of the microstructure when producing functionally graded coatings. |