REACTIVE HOT PRESSING AND OXIDATION BEHAVIOR OF Hf-BASED ULTRA-HIGH-TEMPERATURE CERAMICS

A HfB2-SiC ceramics were fabricated via a reactive hot pressing using Hf, B4C, and Si as precursors. The reaction temperature for the reactive hot pressing between 1800 and 1900 degrees C was determined by reaction of the precursor at different temperatures from 900 to 1800 degrees C. The effective size reduction of precursors was investigated by vibration milling, which exhibited a critical role to achieve high densification and uniform microstructure. Also, it has affected the oxidation behavior of HfB2-SiC in air. Vibration milled sample showed uniform surface of SiO2 layer, but sample which was fabricated by as-received powder exhibited non-uniform oxidation behavior. Examination of the mechanical properties showed that particle size reduction via vibration also led to improved flexural strength, hardness and fracture toughness.