Fabrication of Reaction‐Sintered Sialon

Abstract

A factorial design experiment was conducted to determine the major parameters affecting the densification of mixtures having the composition (in mol%) 50 Si 3 N 4 , 25 A1 2 O 3 , and 25 A1N. Improved densities of the resulting sialon were achieved using a longer milling time and SN‐502 Si 3 N 4 powder. However, sialon samples prepared from the SN‐502 powder contained some of the X‐phase, whereas those fabricated from AME Si 3 N 4 powder did not. This difference is considered to be due to the higher SiO 2 content of the SN‐502 powder and its greater susceptibility to partial hydrolysis during the milling process. Reaction‐sintered sialon (97.2% theoretical density) fabricated using AME powder had a room‐temperature bend strength of 352 MN/m 2 (51,000 psi) and exhibited slow crack growth at 1300° and 1400°C. It is suggested that this is not an inherent property of sialon but is due to the presence of a calcium‐containing grain‐boundary phase, as in hot‐pressed Si 3 N 4 .