Role of Si3N4 on Microstructure and Hardness of Hot-pressed ZrB2−SiC Composites

The impact of Si3N4 content on the hardness and microstructural developments of ZrB2-SiC material has been investigated thoroughly in the present investigation. Having prepared the raw materials in a jar mill, the ZrB2-SiC samples containing various amounts of Si3N4 were hot-pressed at 1850 °C. Furthermore, XRD, FESEM, and HRTEM were utilized to evaluate the microstructure of samples. The formation of in-situ h-BN was proved by the mentioned methods. Also, it was shown that the Vickers hardness of ZrB2-SiC increases up to 20 GPa in presence of 4.5 wt% Si3N4 which is 3 GPa more than the sample without Si3N4. Results show that the positive effect of increased relative density on hardness is more than the negative effect of h-BN soft phase formation

Effect of iron nanoparticles on spark plasma sinterability of ZrB2-based ceramics

This study assesses the influence of added iron (Fe) nanoparticles on the sinterability, microstructure, and mechanical characteristics of SiC-enforced ZrB2 ceramics. The specimens were sintered under 30 MPa at 1700 degrees C for 5 min using the spark plasma sintering method. The SiC-free sample presented near full density; however, the incorporation of SiC led to a similar to 3% drop of the relative density. Although SiC could remove the surface oxides, the generation of a noticeable volume of gaseous phases resulted in increasing the amount of residual porosity. According to the X-ray diffractometry, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and field emission electron probe microanalyses studies, the ZrFe2 and FeB compounds were generated as the in situ phases in the ZrB2-Fe specimen, whereas the chemical reactions among the available constituents led to the in situ generation of graphite, FeSi2, and Zr3Fe phases in the ZrB2-SiC-Fe composite. The SiC-reinforced sample achieved a Young's modulus of 480 GPa and hardness of 29.4 GPa. Finally, the nanoindentation test was simulated using a 3D axisymmetric finite element model wherein the results obtained for the finite element modeling and load-displacement curve were in good agreement with the practical results. The mean values of elastic modulus, hardness, and stiffness in practical results were found to be 480 GPa, 29.4 GPa, and 0.72 mN/nm, while the corresponding ones in simulations were 571 GPa, 21.9 GPa, and 1.51 mN/nm, respectively.N