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Abstract The ZrB 2 -SiC nano composite was produced in a pressureless sintering method. The micro AlN powder was used as an additive. In order to investigate the effect of the simultaneous presence of nano and micro particles of SiC, the ZrB 2 powder with various percentages of nano and micro SiC particles were mechanically milled in a planetary mill for 2 h at a speed of 200 rpm. The resulting mixture was subjected to an initial hot press at 80 °C and a pressure of 100 MPa and then cold isostatic pressing was done (CIP) and the resulting sample sintered at 2150 °C. The AlN particles were then added to ZrB 2 -SiC composite and its microstructure and mechanical properties were evaluated. The results show that by changing the volume percentage of nano SiC particles from 20% to 15% and 5% for the micro particles, the porosity decreases and the density increases. Microstructural analysis and mechanical properties of the samples showed the highest hardness (15.9 GPa) and fracture toughness (4.9 MPa.m1/2) for the sample with 15 and 5 vol% of nano and micro SiC particles respectively. Addition of 7.5 vol% of AlN particles resulted to the density of 98.1% and the hardness and toughness values increased to 17.1 GPa and 5.7 MPa.m1/2. Highlights • ZrB 2 -SiC-AlN nanocomposite were produced by pressureless sintering method. • The effect of SiC particle size and AlN particles addition were investigated. • Addition of 7.5 vol% of AlN resulted to the density of 98.1% and the hardness and toughness values increased to 17.1 GPa and 5.27 MPa.m1/2. [ABSTRACT FROM AUTHOR]

In the present paper, ZrB 2 –SiC–C sf composites were produced by pressureless sintering method. Carbon fiber and SiC nanoparticles with different weight percentages were added to the milled ZrB 2 powder. The mixed powders were formed by hot pressing and cold isostatic press (CIP) and after the pyrolysis, were sintered at 2100 °C and 2150 °C. In order to compare the microstructure and mechanical properties of samples scanning electron microscopy (SEM) equipped with EDS spectroscopy, XRD analysis, hardness and toughness tests were used. The results show that with the increase in weight percentage of carbon fiber, the porosity increases but the hardness, fracture toughness and density decrease. On the other hand, with the increase in weight percentage of SiC nano-particles, the porosity decreases and fracture toughness, hardness and density increase. The results indicate that in an optimal percentage of both additives, the hardness and toughness increase. Additionally, with the increase in sintering temperature, the values of hardness and fracture toughness increase and porosity decreases. [ABSTRACT FROM AUTHOR]