Microstructural development and mechanical properties of reactive hot pressed nickel-aided TiB2-SiC ceramics

Abstract

TiB2-SiC composites with different amounts of Ni (0, 2 and 5wt.%) added as sintering aid were fabricated by reactive hot pressing (RHP). The mechanical properties were assessed under ambient conditions and the flexural strength was further tested in the temperature range of 700–1000°C. The microstructures of the composites were characterized by a scanning electron microscope (SEM), transmission electron microscope (TEM) and energy-dispersive spectrometer (EDS). The flexural strength degradation mechanism occurring at elevated temperatures was studied. Addition of a moderate amount of Ni led to an improvement of the mechanical properties at room temperature. For the investigated ceramic composites, TiB2-SiC-5 wt.% Ni sample showed significantly enhanced mechanical properties, i.e., a flexural strength of 1121±31MPa, a fracture toughness of 7.9±0.58MPa·m1/2, a hardness of 21.3±0.62GPa, and a relative density of 98.6±1.2%. Ni distributed along grain boundaries improved the interface strength. The improved fracture toughness was ascribed to crack deflection, grain rupture and crack shielding effect of Ni. A substantial strength degradation occurred at elevated temperatures, which was attributed to softening of the grain boundaries, surface oxidation and sliding of grain boundaries. The elastic modulus was found to decrease with increasing temperature.