β-Si_3N_4 晶粒生长对热压自韧 Si_3N_4 力学性能的影响

研究了１５ｍｏｌ％Ｙ２Ｏ３－Ｌａ２Ｏ３热压自韧Ｓｉ３Ｎ４的β－Ｓｉ３Ｎ４晶粒生长对强度、韦伯模量和断裂韧性的影响。在最佳的工艺条件下，其强度、断裂韧性和韦伯模量分别为９６０ＭＰａ、１１．７２ＭＰａ·ｍ１／２和２４．５。实验结果表明，烧结温度和时间对β－Ｓｉ３Ｎ４晶粒生长及力学性能有重要影响。随烧结温度升高，其强度、断裂韧性和韦伯模量值上升；超过１８００℃，其力学性能有一定下降。过长的烧结时间，将使β－Ｓｉ３Ｎ４晶粒粗大，因而其性能降低。韦伯模量取决于β－Ｓｉ３Ｎ４晶粒尺寸分布和显微结构均匀性。ＳＥＭ观察表明，裂纹偏转是该材料的主要增韧机制。另外，较大β－Ｓｉ３Ｎ４晶粒的拔出和裂纹分支也对增韧有所贡献。

EFFECT OF GRAIN GROWTH OF β-Si 3N 4 ON MECHANICAL PROPERTIES OF IN-SITU TOUGHENED Si 3N 4 BY HOT-PRESSING

It is investigated that the effect of grain growth of β-Si 3N 4 on strength, Weibull modulus, and fracture toughness of in-situ toughened Si 3N 4 containing 15mol% Y 2O 3-La 2O 3 additives by hot pressing. At the optimum processing conditions, this material has a flexural strength of 960 MPa, a fracture toughness of 11.72 MPa·m 1/2 , and a Weibull modulus of 24.5. The experimental results show that the sintering temperature and holding time have signifficant effects on grain growth of β-Si 3N 4 and mechanical properties. With the sintering temperature increasing, the flexural strength, fracture toughness, and Weibull modulus of in-situ toughened Si 3N 4 increase ; whereas above 1800℃ , the mechanical properties decrease slightly. When the holding time is too long,the β-Si 3N 4 grains become coarse and the properties will decrease.The Weibull modulus depends on the size distribution of β-Si 3N 4 grains and uniformity of microstructures.SEM observations show that crack deflection is primary toughening mechanism,and pullout of elongated β-Si 3N 4 grains and crack branching also contribute to toughening.