SiC – Zn Nanocomposites Obtained Using the High – Pressure Infiltration Technique

Two-nanophase SiC-Zn composites were synthesized under pressure up to 8 GPa at up to 1000oC using an high-pressure infiltration method. The advantage of this technique is that in a single, continuous process the ceramic nanopowder is compressed to form the matrix with nanopores; the nanopores are filled with a liquid secondary phase, (here Zn), which crystallizes as nano-scale grains. The key limitation is that the pores in the infiltrated preform have to stay open during the entire process. For this reason only powders of very hard ceramic materials can be used as a matrix. Two types of SiC nanopowders with average crystallite size of 10 nm and 60 nm and average particle size of 30 nm and 100 nm, respectively were used. The measurements of porosity of the green compacts prepared from these powders, pressed at 2.5 GPa and 8 GPa at room temperature, indicated that open porosity was maintained. The nanocomposites obtained show a “nano-nano” type microstructure with a uniform mixture of SiC and Zn phases. The volume fraction of Zn is 20 % independent of the process conditions and initial powder morphology. The process parameters and powder granularity influenced the crystal size of the secondary phase. The average grain size of Zn varied from 20 to 85 nm and was smaller in the composites obtained with the finer matrix, under higher pressure and at lower temperature. The microhardness HV02 of SiCZn nanocomposites varied from 6 to 22 GPa and increased with an increase of pressure and temperature of the infiltration process, and was significantly larger for the finer grained composites.