Design and development of a powder mixing device used in the deposition of high velocity oxy-fuel (HVOF) thermal spray functionally graded coatings; Kabir Al Mamun
Al Mamun, Md. Kabir (2007) Design and development of a powder mixing device used in the deposition of high velocity oxy-fuel (HVOF) thermal spray functionally graded coatings; Kabir Al Mamun. Master of Engineering thesis, Dublin City University.
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The application of Functionally Graded Materials (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. However the HVOF (High Velocity Oxy-Fuel) process does not possess this feature. 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 thermal spray process to produce f~~nctionallgyr aded 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 bui Id-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. Post nod el ling the design was manuFactured and tested experimentally for functionality. In the current research the mixing of different proportions of powders was controlled by a computer using Lab VlEW software and hardware, which allowed the control and repeatability of the microstructure when producing functionally graded coatings.
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