1995 Volume 103 Issue 1202 Pages 1085-1089
Silicon nitride powder calcined with yttria-rich or alumina-rich additives (total 10 mol%) was alternately accumulated into layers by centrifugal filter-pressing; a combination of filter-pressing and centrifugal shape forming. The subsequent sintering at 1800°C in 1.0 MPa N2 atmoshere provided sintered composites (SN-MLCs) with more than 98% density and 60μm thick of each layer. Elongated rodlike grains characteristic of yttria-rich additives were periodically observed in the SN-MLCs at the calcination temperature of 1400°C. At a high calcination temperature (1450°C), the difference in microstructure between layers became smaller. It was considered that the diffusion of a part of the additives through the layer interface reduced the interlayer stress to prevent delamination during sintering. The crack length propagated from Vickers indents on the SN-MLCs was shorter than that on the monolithic materials. The shorter crack length and interlayer fracture observed for SN-MLCs suggested a possibility of toughening.
