Fabrication of high performance silicon nitride ceramics with TiO2 additive by annealing process

The high performance Si3N4 ceramic was prepared firstly for TiO2, Y2O3 and MgO as pressureless sintering additives. Si3N4 ceramic with relative density of 99.6% and flexural strength of 785 +/- 23.3 MPa could be ob-tained with 3 mol% TiO2 and sintered at 1800 degrees C for 2 h. After annealing at 1700 degrees C, the facture toughness of sample of 1 mol% TiO2 increased from 8.31 +/- 0.28 MPa m1/2 to 9.84 +/- 0.16 MPa m1/2. The flexural strength of sample of 2 mol% TiO2 increased from 707 +/- 26 MPa to 981 +/- 16 MPa, thermal conductivity increased from 57.8 W/(m center dot K) to 68.49 W/(m center dot K). The XRD results showed that the ratio of I101/I210 and grain height reached to 1.84 and 5 mu m of the sample of 3 mol% TiO2, respectively. The present investigation revealed that the three-dimensional array of highly oriented crystalline Si3N4 micro rods could be prepared which array on the ho-mogeneous substrates by using TiO2 as agent. This phenomenon may propose a method that the mechanical properties the Si3N4 ceramics added TiO2 can be improved significantly after annealing process.