Sintering of Refractory Compounds at High Pressures and High Temperatures

摘要

A comparison of the microstructures and mechanical properties of high pressure hot pressed and conventionally hot pressed TiB2 was completed. Although the materials were characterized by comparable room temperature bend strengths of 40,000 to 50,000 psi; the high pressure hot pressed material maintained this strength level at 1400C whereas the strength of the conventionally hot pressed material was less than 10,000 psi above 1000C. The behavior of the latter material is most probably associated with a higher impurity content and larger grain size as is commonly found in such materials. The high pressure hot pressed material showed a maximum strength of 70,000 psi at 1000C. The fracture mode of high pressure hot pressed TiB2 was predominately intergranular at room temperature and at 1400C, but fifty per cent transgranular fracture was noted at 1000C. The fracture mode of the conventionally hot pressed TiB2 was 70 per cent intergranular and unchanged from room temperature to 1400C. Ceramic additives particularly silicon carbide were found to enhance the consolidation of TiB2 under the conditions employed for high pressure hot pressing. This particular additive affords fully dense structures at temperatures 100 to 150 degrees lower than for TiB2 with no additive; the composite material is characterized by fine grain structure and improved oxidation resistance relative to TiB2. Several scaled-up fabrications were performed for the TiB2-SiC composite; billets of one inch diameter were fabricated.