Fabrication and Properties of Reactively Hot Pressed HfB2-HfC Ultra-High Temperature Ceramics

Abstract

HfB2-HfC composites were prepared by reactive hot pressing using Hf and B4C at temperatures of 1800 and 1900oC for 60 min under 32 MPa in an Ar atmosphere. The reaction sequences of the HfB2-HfC composite were studied through series of pressureless heat treatments ranging from 800 to 1600oC. The effect of size reduction of the starting powders on densification was investigated by vibration milling. Fully dense HfB2-HfC composites were obtained by size reduction of the starting powders via vibration milling. The oxidation behaviour of the HfB2-HfC composites at 1500oC in air showed formation of a non-protective HfO2 scale with linear mass gain. Examination of the mechanical properties showed that particle size reduction via vibration milling also led to improved flexural strength, hardness and fracture toughness.