Kinetics of nonisothermal hot pressing of boron carbide powder and its mixtures with alumina and additions of metallic aluminum

The paper proposes a method to determine the kinetic parameters of temperature-controlled hot pressing from the current temperature and height of specimens. This method substantially reduces the scope of experimental work in comparison with the conventional method for studying isothermal hot pressing. The kinetics of the densification of boron carbide powder and its composites with 20, 50, and 80 wt.% Al2O3 and 2 wt.% Al is studied during nonisothermal hot pressing. It is experimentally established that the kinetics of densification is controlled by the creep mechanisms in the matrix that forms a porous body. The creep activation energy for the matrix is estimated to be 8.1 eV for boron carbide, 7.6 eV for B4C + 20% Al2O3 + 2% Al, and 6.6 eV for B4C + 80% Al2O3 + 2% Al. The densification of the composite with 50 wt.% Al2O3 is controlled by the weekly temperature-dependent viscous flow of the matrix, for which the estimated activation energy is 1.7 eV. At higher temperatures, the viscous flow of the matrix is controlled by nonlinear creep the activation energy of 4.6 eV, which may correspond to superplasticity. The structure, phase constitution, and some mechanical properties of the composites are studied.