Role of Si3N4 on microstructure and hardness of hot-pressed ZrB2−SiC composites en en 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. 34 40 Zahra Bahararjmand Department of Biophysics Istanbul University-Cerrahpasa Turkey zahra.bahararjmand@ogr.iuc.edu.tr Mohammad A. Khalilzadeh Department of Forest Biomaterials, College of Natural Resources North Carolina State University United States Farshad Saberi Movahed Department of Materials Science and Engineering North Carolina State University United States Tae Hyung Lee Department of Materials Science and Engineering, Research Institute of Advanced Materials Seoul National University Republic of Korea Jinghan Wang Department of Materials Science and Engineering, Research Institute of Advanced Materials Seoul National University Republic of Korea Sea hoon Lee Division of Powder/Ceramics Research, Korea Institute of Materials Science Republic of Korea Ho Won Jang Department of Materials Science and Engineering, Research Institute of Advanced Materials Seoul National University Republic of Korea Hot-pressing ZrB2-SiC-Si3N4 Microstructure Hardness Vol 1 No 1 Paper 3.pdf [1] K. 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