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1914 |
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Wednesday, May 05, 2010, Moor Room 2:20 PM Properties 3 |
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Microstructures of cold sprayed coatings investigated by X-ray microtomography |
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Vincent Guipont* / MINES ParisTech, PSL Research University, MAT - Centre des matériaux, CNRS UMR 7633, C2P - Competence Center for spray Processing, BP 87 91003 Evry, France , FRANCE Gilles Rolland / MINES ParisTech, France Michel Jeandin/ MINES ParisTech, France Dominique Jeulin/ MINES ParisTech, France Charles Peyrega/ MINES ParisTech, France Wolfgang Ludwig/ ESRF, France |
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Cold sprayed materials exhibit unique microstructures because they are generated through a cumulative piling-up of highly-deformed powder particles. Primary building-up with plastic deformation of the particle occur at the impact. Further metalworking of deposited particle is promoted by subsequent peening from others impacting particles. This coating build-up enables a complex embedding with a steady contact between deformed particles. The resulting three-dimensional architecture of cold spray coatings is a key issue to address the problem of engineered highly dense gastight or liquidproof coating applications. This is particularly critical in case of thin cold spray coating (<100 ?Ým). This is also notably true for composite coatings involving mixed powders with different materials having dissimilar properties (size, density, plastic behaviour upon impact,¡K). In this work, high-resolution X-ray Microtomography (XMT) experiments are described with details as a non-destructive technique for microstructural investigation through attenuated contrast imaging. Investigations have been achieved at the European Synchrotron Radiation Facility (beam line 19) to carry out imaging of various cold spray coatings with metals of various atomic numbers: Al, Ni, Ag,¡Kand composites involving mixed powders. The resulting large scanned volumes (2048¡Ñ2048¡Ñ2048 pixels images) were cropped at different locations within the cold spray coatings and further image analysis was managed to discriminate and quantify each constituent distribution (pores and various phases in case of composite) in large volumes (up to 250¡Ñ250¡Ñ570 ?Ým3). It allowed a sound observation and quantification of cold spray coatings that could be compared to conventional SEM examination. Moreover, the three-dimensional morphology of series of individual embedded particles were also analysed through advanced segmentation of XMT images stacks. From the description of the actual morphology of numerous cold spray particles, the microstructural assessment of cold spray coatings was improved to move from a two-dimensional approach to a three-dimensional approach to cold spray coatings formation and resulting morphological characteristics. |