Direct Evidence on the Elimination of Pore by the Applied Pressure in Hot Isostatic Pressing of Alumina

Abstract

ABSTRACTRemoval of natural pore during capsule hot isostatic pressing (HIP) and normal sintering were examined directly with the novel liquid immersion technique, which can reveal details of micro-structure and characterize flaw-forming defects of microns-size in lightly densified specimens. The results were supplemented by the pore size measurement with the mercury porosimetry, microstructural examination with SEM as well as microstructural examination of specimens after final densification. The behaviors in both pore size and shape changes were different in HIP and normal sintering. Removal of large pores of microns-size started from the beginning of densification in HIP. Whereas large pores grow with densification in normal sintering. Large pores changes their shape drastically in HIP, but hardly changes in normal sintering. The behavior of pore in the early stage of densification is closely related to the microstructure of densified specimen; without HIP, large defects of processing origin are present in near-fully dense specimen. These observations were discussed in terms of current sintering theory.