Spark Plasma Sintering of ZrB2-SiC-Based Ceramics Reinforced with Nano-Diamond

In this research work, the effects of nano-diamond addition on densification and mechanical properties of 25 vol% SiC reinforced ZrB2-based ultra-high temperature composites were studied. In this way, a ZrB2–SiC composite (as the baseline) and three ZrB2–SiC-based composites doped with different amounts of nano-diamond additive (1, 2 and 3 wt% of matrix phase) were fabricated by spark plasma sintering route. The sintering process was carried out at 1900 °C for 7 min under 40 MPa. The addition of nano-diamond, up to 2 wt%, has not significantly affected the densification process because the 0-2 wt% nano-diamond reinforced samples reached their theoretical densities but the relative density of sample reinforced with 3 wt% diamond was less than 99%. The hardness of 0, 1, 2 and 3 wt% diamond reinforced ceramics were 19.5, 23.4, 24.7 and 22.2 GPa, respectively. All diamond reinforced samples were harder than the diamond-free one but the hardness slightly decreased by the addition of 3 wt% diamond. The fracture toughness linearly increased from 4.3 MPa.m1/2 for diamond-free ceramic to 5.8 MPa.m1/2 for3 wt% diamond reinforced sample. The sintering route was a reactive process as the nano-diamond was transformed to the graphite during the sintering and/or converted to the in-situ formed ZrC and B4C phases through the removal of oxide impurities from the surfaces of raw materials.