On the thermal and chemical stability of diamond during processing of Al/diamond composites by liquid metal infiltration (squeeze casting)

Abstract

Aiming at assessing the feasibility of Al/diamond composites, the present study deals with the thermal stability of different diamond grades under environmental conditions which are characteristic for the selected pressurized liquid melt infiltration technique (squeeze casting). The influence of both the diamond grade, i.e., synthetic and natural, mono- and polycrystalline diamond and the particle size is investigated. The critical parameters with respect to thermal degradation of diamond have been identified. It is shown that as a consequence of their peculiar process history, “micron-grade” diamond powders are particularly susceptible to thermal degradation in the presence of oxygen and that such degradation is most effectively prevented by using hydrogen-containing atmospheres such as forming gas. It is outlined why nanosized diamond powders and polycrystalline diamond powders are not a suitable “reinforcing phase” for Al/diamond composites. Eventually, it is shown that under the conditions prescribed, the liquid metal infiltration technique is principally viable for the processing of sound Al/diamond composites.