Layered machinable ceramics for high temperature applications

Recently the authors reported on the fabrication and characterization of a layered ternary compound Ti{sub 3}SiC{sub 2}, that was found to combine many of the best attributes of metals and ceramics. Like metals it is an excellent electric and thermal conductor, easily machinable, relatively soft, not susceptible to thermal shock and behaves plastically at higher temperatures. Like ceramics it is oxidation resistant, refractory, and, most importantly, it maintains its strength to temperatures that render the best superalloys available today unusable. Upon realizing the remarkable properties exhibited by Ti{sub 3}SiC{sub 2} the authors carried out a literature search for other compounds with the same chemistry. They found one only, namely: Ti{sub 3}GeC{sub 2} which has properties that are very similar to Ti{sub 3}SiC{sub 2}. The purpose of this paper is two-fold. The first is to demonstrate the similarities between the properties of the H-phases, Ti{sub 3}GeC{sub 2} and Ti{sub 3}SiC{sub 2}. The second is to present some compelling microstructural evidence that indicates that these compounds behave as polycrystalline nanolaminates. To that effect the authors fabricated and characterized the following H-phases: Ti{sub 2}AlC, Ti{sub 2}AlN, Ti{sub 2}GeC and as well as Ti{sub 3}GeC{sub 2}. In addition they fabricated V{sub 2}AlC, Ta{sub 2}AlC,more » and Nb{sub 2}AlC and tested their machinability.« less