In-situ synthesis of Si3N4–SiC composites by reactive hot-pressing
Hiroshi Mabuchi, Hiroshi Tsuda, Takeshi Ohtsuka, Toshiyuki Matsui, Kenji Morii
Reactive hot-pressing was carried out with elemental powders to prepare Si3N4 – SiC composite ceramics. Silicon and graphite powders with sintering additives (Al2O3 and Y2O3) were reacted at 1873 K in gaseous nitrogen (0.15 MPa) and hot-pressed at 2073 K for 7.2 ks with applied pressure of 70 MPa, and finally formed a Si3N4(β – Si3N4) – SiC(β – SiC) composite with a small amount of glassy and crystalline phases from additives. The resulting composites had 12, 21, and 34 vol% SiC. The Si3N4 matrix grains were rod-like in shape with sizes of about 0.3 – 5 μm, and with aspect ratios of about 5 – 10. The SiC grains were granular with sizes of about 0.1 – 1 μm, and homogeneously distributed and well bonded to the matrix. It was found that the composite ceramics had a relatively high bending strength both at ambient and elevated (1423 K) temperatures; about 1000 and 700 MPa, respectively. Fracture toughness of 5.3 MPa m1/2 was obtained by indentation fracture tests. It was evident that reactive hot-pressing is a very effective process for in-situ synthesis of Si3N4 – SiC composite ceramics.