Spark plasma sintering of Si3N4-B4C composites

Abstract

In this study the production of Si 3 N 4 -B 4 C composites using spark plasma sintering technique was studied. This technique was preferred in order to minimize the reactions between starting constituents. Fully dense Si 3 N 4 ceramic was obtained by SPS. The bulk densities of all the produced composites was found to be significantly less than that of Si 3 N 4 , and this was attributed to the formation of the relatively low-density reaction products. In the B 4 C-containing composites there was a trend for the bulk density to increase slightly with decreasing particle size of B 4 C powder. Composites containing both B 4 C and TiO 2 had somewhat higher bulk densities when compared with those just containing B 4 C. This was related to the formation of relatively high-density reaction products in significant amounts. The fine B 4 C added to the Si 3 N 4 base composition containing Al 2 O 3 and Y 2 O 3 as sintering additives, even when incorporated in significant amounts, was consumed readily during the fast sintering process. Using coarse B 4 C particles reduced the reaction kinetics to some extent. As a result of reactions between Si 3 N 4 and B 4 C particles SiC, h-BN and metallic Si were formed. When both B 4 C and TiO 2 were added together additional phases of Ti (C, N) and TiB 2 were formed. Possible reactions that explain the formation of the in-situ phases were proposed through thermodynamic considerations.