Low-temperature pressureless sintering of Al2O3-SiC-Ni nanocermets in air environment

This paper introduces a simplified method for low-temperature pressureless sintering of Al2O3-Ni-SiC nanocermets in air environment. In this method, a thin and continuous Ni shell was coated on the surface of Al2O3 particles using electroless deposition method. The composite powders were subsequently compressed to prepare bulk specimens. By preventing the ceramic particles from direct contact during the densification of green specimens, sintering temperature of cermet materials was reduced from that of Al2O3 (> 1400 °C) to the range of Ni solid-phase sintering temperature. Furthermore, dissolution of a low amount of phosphorus in the composition of Ni coatings caused the further decrease of the sintering temperature to 800 °C. At such low temperatures, pressureless sintering of the cermets in the air environment was successfully performed instead of the common hot pressing process in a reducing atmosphere. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD) characterizations indicated that the microstructure of such sintered samples consists of a continuous Ni network surrounding Al2O3 grains, without any structural defects or Ni oxidation. Furthermore, mechanical properties of the cermet materials were improved through reinforcement of the continuous Ni network by different amounts of SiC nanoparticles. The results showed that Al2O3-Ni-5 wt% SiC nanocermets sintered at 800 °C obtain the highest compressive strength of 242.5 MPa, hardness of 56.8 RA, and the lowest wear weight loss of 0.04 mg/m.