Pressureless sinterability of slip cast silicon nitride bodies prepared from coprecipitation-coated powders

The sinterability of compositions from different powder preparation methods (coprecipitation-coating of Si3N4 powder or mechanical mixing of Si3N4 wit h Y2O3 and Al2O3) and compaction routes (dry pressing or slip casting) was compared. Both the coating method and the slip casting process improved sil icon nitride sinterability over the mechanical mixing method and dry pressi ng route. However, the minimisation of powder agglomeration in the green bo dies achieved by slip casting is more determinant to the sintering behaviou r than the homogeneous distribution of the sintering additives around the S i3N4 offered by the coated powder. The coating powder method in combination with the slip casting process is the most favourable processing route, lea ding to a homogeneous and fully dense microstructure by pressureless sinter ing at a relatively low temperature of 1750 degrees C. This technique produ ced materials with hardness of 15.2 GPa, fracture toughness of 7 M Pa m(1/2 ) and flexural bending strength of 910 MPa. (C) 1999 Elsevier Science Limit ed. All rights reserved.