The processing of SiC/SiC ceramic matrix composites using a pulsed Nd YAG laser Part I: Optimisation of pulse parameters

The machining of a composite material comprising silicon carbide (SiC) fibres in a chemical vapour infiltrated SiC matrix has been investigated using a 400 W pulsed Nd-YAG laser. The principal aim of this work has been to determine, by comparison with the results obtained from other ceramic matrix composites optimum processing conditions for these materials with regard to both material removal rate and cut surface quality. Previous trials involving a borosilicate glass matrix composite and a magnesium-alumino-silicate glass-ceramic matrix composite, both incorporating the same SiC fibres, have highlighted the importance of the coupling of the matrix phase with the emitted laser radiation. The various phase's resistance to oxidative degradation at high temperatures is another influential factor. The material considered in this work has been shown to be particularly suitable in these respects, with the result that both cut rate and quality are significantly enhanced. Report is made of the effect of varying the laser pulse parameters such as pulse energy, duration and intensity and concentrates on the material removal rate. Part II of this work addresses the influence of process variables, such as choice and pressure of assist gas and the point of focus of the laser beam on the quality of the cut surface. (C) 1998 Chapman & Hall.