Dynamic failure and fracture of the TiC-steel composite

The dynamic response of a titanium carbide (TiC)- steel ceramic-metal composites (cermets), prepared by pressureless infiltration of TiC ceramic preforms by molten steel, was studied in planar impact experiments, using copper impactors with velocities in the 80 to 450 m/sec range. The effect of the microstructure of the metallic component on the Hugoniot Elastic Limit (HEL) and on the spall strength of the cermet samples was studied by use of the VISAR (Velocity Interferometer System for Any Reflector) for measuring the velocity of the free surface of the samples. The study revealed that the confining stress, developed in the carbide component of the cermet by the strain-hardened steel matrix under tension, affects strongly the dynamic response of the cermet. The value of the confining stress that was estimated on the base of two types of spall measurements correlates with the increase of the HEL with respect to that of the cermet containing a stress-free ceramic sub-matrix. This correlation leads to two definite conclusions: i. The TiC component of the cermet fails in compression like a brittle material, while the inelastic response of the cermet is similar to that of a metal. ii. The dynamic response of the cermet may be controlled by choosing an appropriate thermal treatment.