Strength and Creep in Boron Carbide (B4C) and Aluminum Dodecaboride (alphaAlB12)

Some thermomechanical properties of boron carbide and aluminum dodecaboride are presented. The dependence of the bending strength on the temperature of B4C and AlB12 in the ductile rupture region was studied. It was detected that the ductile rupture of B4C starts at temperatures above 1500?C while that of AlB12 begins at 1400?C. Total deformation, however, did not exceed 2% even at 1800?C. The investigation of the creep of B4C and AlB12 showed that the rate depsilon/dt of steady creep depends on the applied stress and the temperature: depsilon/dt=Asigman exp(-E/RT). Besides, creep in boron carbide at stress values lower than 90 MPa occurred by the vacancy-diffusive mechanism, for which n=1. At stress values over 90 MPa, n=3 and the creep mechanism changes to dislocation creep. A similar phenomenon is observed in the case of aluminum dodecaboride; however, the replacement of the vacancy-diffusive mechanism by dislocation creep takes place at stress values of 80 MPa.