Hot Isostatic Pressing of Sintered Ceramics

摘要

The final stage densification of undoped Al2O3, MgO-doped Al2O3, and magnesium aluminosilicate glass/Al2O3 composites by hot isostatic pressing unencapsulated, closed porosity samples has been investigated. The conditions for pore stability have been reviewed for these systems that are representative of ceramics densifying by solid state diffusion and solution-precipitation mechanisms. An extensive series of experiments were conducted and the results used to test the validity of models derived to understand the effect of 1) dihedral angle, effective stress, grain size distribution and pore/grain size ratio on pore stability during hot isostatic pressing of pure and MgO-doped alumina. Models explained that influence of these parameters although 100% was not observed as a result of porous heterogeneities exceeding the critical pore/grain size ratio of density approx 2.3. 2) Dihedral angle, effective stress, grain size, volume percent liquid, gas diffusion ad liquid redistribution during hot isostatic pressing of alumina glass composites. Models for pressureless and pressure enhanced solution precipitation were derived to incorporate the effective stress. Experiments at various pressures agree will with the new models and demonstrate that dedensification is limited by the interface reaction for short (i.e., < 1 hr) HIP times. Longer HIPIng experiments resulted in densification as a result of pressure enhanced gas diffusion into the glass matrix. At > 98% relative density macropore (100 micrometer diameter) closure can occur by pressure driven liquid redistribution. Keywords: Grain boundary.