Creep studies in Si3N4 - TiB2 materials

Two-phase Si3N4 - TiB2 composites were prepared by high pressure (P=4 GPa) at 1800 C. One type of TiB2 powder (S=1.1 m2/g) and two types of Si3N4 powders (S=1.7 m2/g- compositions I, and S=23.5 m2/g - compositions II) have been used for the preparation of Si3N4 - TiB2 composites (25, 50, and 75 vol%). Compression tests were conducted at 1500 -1600 C (σ=5-20 MPa, t=30 min). Experiments have shown that, whereas the creep rate (ε) of compositions I was very small and was nearly constant on content, yet that of ones II was characterized by clear marked maximum (ε ≅ 1.7x10-4 s-1) for Si3N4 - 75 vol% TiB2 samples. This anomaly is expected to connect with superplasticity. (orig.)