两步烧结对 La_2O_3-Y_2O_3 自增韧氮化硅显微结构和性能的影响

The Effects of TwoY 2O 3

两步烧结对Ｌａ２Ｏ３Ｙ２Ｏ３自增韧氮化硅显微结构和性能的影响＊吕杰①张立同②成来飞③周万城③关于颗粒尺寸分布β相含量及形态等初始粉料特性对Ｓｉ３Ｎ４显微结构的影响已作了大量的研究，但这些研究都是通过一步烧结方式进行的。作者采用两步热压烧结的方法对Ｌａ...

Since 1990, we have been seeking ways for improving high temperature properties of ceramics needed by Chinese aeroengine. Since 1994, we have tried to replace the commonly employed onestep sintering with twostep sintering as one means to obtain the above mentioned improvement. Specifically, we studied Si 3N 4 containing La 2O 3Y 2O 3. With twostep sintering, we obtained sintered body with insitu composite microstructure, which, in our opinion, looks promisingly helpful in the search for good high temperature properties. Of course insitu composite structure can also be obtained with onestep sintering, but that obtained with twostep sintering we deem to be significantly better. This is perhaps because, according to our analysis, the growth of βSi 3N 4 grains in twostep sintering is quite different from that in onestep sintering. The difference, in our opinion, derives from the following experimental observations: (1) In onestep sintering, phase thansformation occurs first and then grain growth occurs, both at the same temperature; (2) In twostep sintering, phase transformation occurs first at one temperature (1 700 ℃ in our experiments) and then grain growth occurs at a somewhat higher temperature (1 800 ℃ in our experiments). It is an encouraging sign that fracture toughness, measured by us at room temperature, is 12.3 MPa m for twostep sintering as against 11.2 MPa m for onestep sintering.