ELIMINATION OF LARGE ARTIFICIAL PORES DURING THE HOT ISOSTATIC PRESSING OF PRESINTERED ALUMINA

Shrinkage of large pores during hot isostatic pressing (HIP) of presin tered alumina has been studied. When alumina specimens containing arti ficially produced large spherical pores are HIP treated, pore shrinkag e occurs predominantly by plastic deformation. When the temperature of the HIP treatment is 1850-degrees-C, the pores appear to collapse wit h particle fragmentation and sliding. The complete elimination of larg e pores is hard to achieve, because the pressure of N2 gas entrapped i n the pores increases with their shrinkage. The practical implication of these results is that large voids or cracks inside ceramics can be removed by using the proper pressure/temperature regime.