J. Materials Synthesis and Processing, 5, 197-216 (1997)

Michel W. Barsoum and Tamer El-Raghy

Dept. of Materials Engineering, Drexel University

   
ABSTRACT
 
 Recently [1,2]  we reported on two classes of layered ternary compounds,  namely Ti₃SiC₂,  Ti₃GeC₂  and Ti₃AlC₂ henceforth referred to as the 312's,  and the H-phases, M₂B_X where M is a transition metal,  B is a group B element and X is either C or nitrogen.  In both cases,  the structure is hexagonal with alternating layers of transition metal carbide (or nitride) layers interleaved with close-packed planes of the B-group element.  In this paper we expand on our original findings and summarize our understanding of these layered materials to date.  As a class these ternaries have relatively low hardnesses (4-6 GPa),  high electrical conductivities (2-5 x 106 ___m^-1)  and are as readily machinable as graphite.  At temperatures above 1200 ºC they deform plastically with yield points that are quite high ( 100 MPa at 1300 ºC) for that temperature.  In addition, Ti₃SiC₂  is not susceptible to thermal shock,  has good oxidation resistance (1 x 10-8 kg²m^-4s^-1 at 1000 ºC) and is a good thermal conductor (43 W/m K).  It is also a damage tolerant material.  At this time there is little doubt that the deformation mechanism in these materials is dominated by slip along the basal planes.  An apt descriptor of these materials is  "polycrystalline nanolaminates",  if it is understood that the lamina are flexible and can shear with ease relative to each other.