HIP Sinterbility of Silicon Nitride α→β Phase Transformation
1989 Volume 75 Issue 2 Pages 314-320
Details
1989 Volume 75 Issue 2 Pages 314-320
The effects of β phase transformation on HIP sinterbility of silicon nitride were studied using three different powder sizes. The influence of pressure, temperature and holding time on the sinterbility of silicon nitride powders were also investigated.
In order to examine the sintering process, HIP sintering experiments were also conducted under conditions to produce low densities of the sintered bodies. The HIPping conditions were 1 723-1 973 K, 60-200 MPa, holding time 0-3 h, and alumina as well as yttria were used as additives up to 6 mol%.
Within the range of the present work the following was revealed:
(1) The relative density changes linearly with the phase transformation at the initial stage of HIP sintering. At the final stage of HIPping, the phase transformation to β advances drastically faster than the densification does.
(2) Phase transformation to β is mostly affected by the HIPping temperature, and next by the holding time.
(3) The HIPping pressure has little influence on the β phase transformation, and sometimes reduces the phase transformation.
(4) Fracture toughness improves with the increase of the β phase content. Micro hardness is highest around 40-50% of the β phase fraction.
