Grain growth during capsule-free hot isostatic pressing

This paper provides a new insight to the capsule free hot isostatic pressing (HIP) of alumina and yttria-stabilized zirconia ceramics. The first part of the paper focuses on the pre-sintering stage, namely the impact of conventional (2, 5, 10 degrees C/min) and rapid heating rate (100 degrees C/min) on pore closure and grain growth. It is shown that the rapid heating neither changes the pore closure behavior nor restricts the grain growth compared to conventional pre-sintering. The second part investigates the influence of temperature, dwell time, and applied pressure on the microstructure development during HIP. Our findings indicate the existence of a kinetic window, providing the optimal HIP conditions (1200-1250 degrees C, 200 MPa, 1-4 h for investigated powders) for production of almost fully dense compacts with only minimal grain growth. Our results also show that the applied pressure (up to 200 MPa) does not facilitate the grain boundary mobility of the investigated materials even at a higher temperature (1300 degrees C) at which the grain growth normally occurs. The potential of optimized capsule-free HIP was demonstrated by preparation of a transparent c-YSZ sample by a combination of rapid pre-sintering and optimized post-HIP.

Automated summary

This paper investigates the capsule free hot isostatic pressing (HIP) process of alumina and yttria-stabilized zirconia ceramics and provides important insights. It is found that rapid heating does not affect pore closure behavior or restrict grain growth compared to conventional heating. The study also reveals the optimal HIP conditions for producing nearly fully dense compacts with minimal grain growth. Additionally, applied pressure does not enhance grain boundary mobility during the HIP process.