High Strength, High Toughness in Situ Ceramic Composites.

Abstract

Abstract : Raw materials were purchased and two batches were prepared by wet mixing of the powders for the following two compositions; 3TiC+2Si (composition 32) and 3TiC+3Si (composition 33). Thermal analysis (DTA/TGA) of these two batches were performed up to 1 5000C at a scan rate of 100C/min to determine the critical temperature range where the reactions start. Simultaneous TGA/DTA of the 3TiC+2Si and 3TiC+3Si powder mixtures showed presence of exothermic peaks at 7000C for both mixtures. 3TiC+3Si system showed a strong endothermic peak at 14800C. This peak is attributed to the melting of excess silicon. However, further investigation is underway to clarify the nature of the peaks observed. Hot pressing of dry mixed 3TiC+2Si powder composition was performed by using a hot pressing schedule developed by Battelle as the starting point. The hot pressed sample was ground and cut with a diamond saw to make flexural strength test samples according to the MW STD 1942 B. Flexural strength measurements are being carried out at Battelle as of this writing. Optical microscopy examination of the polished surface indicates the presence of extremely fine microstructure in hot pressed samples. Four distinct features were determined within the resolution limits of optical microscope; (1) the presence pores larger than 50 microns, (2) acicular shaped disperse phase throughout the microstructure, SiC particles, (3) continuous matrix phase, Ti3SiC2 phase and (4) round shape shiny particles, most likely unreacted phase. X-ray diffraction analysis of the samples are currently being conducted to determine the phases present after the hot pressing. The more characterization of these samples will be carried out during the next phase of the study. (MM)