CREEP STUDIES IN SI3N4-TIB2 MATERIALS

Two-phase Si3N4-TiB2 composites were prepared by high pressure (P=4 GPa) at 1800 degrees C. One type of TiB2 powder (S=1.1 m(2)/g) and two types of Si3N4 powders (S=1.7 m(2)/g- composites I, and S=23.5 m(2)/g - composites II) have been used for preparation of Si3N4-TiB2 composites (25, 50, and 75 vol%). Compression tests were conducted at 1500 degrees-1600 degrees C (sigma=5-20 MPa, t=30 min). Experiments have shown that, whereas the creep rate (epsilon) of compositions I was very small and was nearly constant on content, yet that of ones II was characterized by clear marked maximum (epsilon similar or equal to 1.7x10(-4) s(-1)) for Si3N4 - 75 vol% TiB2 samples. This anomaly is expected to connect with superplasticity.