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22 January 2005 Column growth mechanisms during KrF laser micromachining of Al2O3-TiC
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This paper aims to contribute to the understanding of column formation mechanisms in Al2O3-TiC ceramic composites due to processing with excimer laser radiation. The mechanisms proposed in the literature to explain the formation of such columns can be grouped in four categories: shadowing mechanisms, hydrodynamic mechanisms, vapour phase deposition mechanisms, and spatial modulation of absorbed energy mechanisms. In the case of Al2O3-TiC ceramics, the hydrodynamic and vapour phase deposition mechanisms can be excluded because experimental results show that the column core is composed of material in a pristine condition. A theoretical simulation of the spatial modulation of absorbed energy due to radiation reflected from preexisting topographic artefacts reveals that this mechanism can explain the growth of columns from those artefacts, but does not explain column growth in Al2O3-TiC, because it predicts that the height of the columns will increase indefinitely with increasing number of pulses, whereas it has been experimentally observed that columns only grow during the first 100-200 laser pulses. This model does not explain the observed variation of the columns height with laser fluence either. By contrast, predictions of the shadowing mechanism with TiC globules formed during the first laser pulses shielding the substrate and favouring column growth are in semiquantative agreement with experimental observations. The evolution of surface topography in Al2O3-TiC ceramics composite during processing with KrF excimer laser radiation is controlled by the ablation behaviour of individual phases and by the chemical changes of the material surface during laser processing.
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V. Oliveira, F. Simoes, and Rui Vilar "Column growth mechanisms during KrF laser micromachining of Al2O3-TiC", Proc. SPIE 5715, Micromachining and Microfabrication Process Technology X, (22 January 2005);

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