RESPONSE OF ALUMINUM-INFILTRATED BORON-CARBIDE CERMETS TO SHOCK-WAVE LOADING

Shock-recovery and shock-spallation experiments were performed on two compositions of aluminium-infiltrated B4C cermets as a function of sho ck pressure. Sixty-five per cent volume B4C-Al cermets were recovered largely intact after shock loading up to pressures of ca. 12 GPa which permitted a critical study of the microstructural changes produced by the shock. Significantly, shock loading to between 12 and 13 GPa prod uced a combination of dislocation debris, stacking faults and deformat ion twins in a small fraction of the B4C grains. Fragmentation of shoc k-loaded 80% B4C-Al samples prevented meaningful microstructural inves tigation. Spall-strength testing also provided indirect evidence for t he Hugoniot elastic limits (HEL) of these composites. Spall-strength c alculations based on an elastic equation of state for 65% B4C-Al indic ated that the elastic regime extended up to shock pressures of ca. 10 GPa, or approximately 65% of the HEL of polycrystalline B4C. A complet e loss of spall strength was then observed at the transition to a plas tic equation of state at a pressure of 12 GPa which coincided with obs ervations of plasticity within the B4C-substructure. This study demons trated that composites containing a highly ductile phase combined with a high compressive strength ceramic phase could support high dynamic tensile stresses by resisting the propagation of catastrophic cracks t hrough the brittle ceramic substructure.