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°C was determined by reaction of the precursor at different temperatures from 900 to 1800°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.