High-temperature spark plasma sintering of h-BN composites reinforced with carbon nanotubes, carbon fibers, and graphene nanoplates en en In this study, two h-BN-based composites reinforced with carbon fibers (CF) and carbon fibers/carbon nanotubes (CNTs)/graphene nanoplates (GNPs) have been produced successfully through a high-temperature spark plasma sintering. 1 wt% short carbon fibers (length of 5 mm) with 0.1 wt% of CNTs and also 0.1 wt% of GNPs as hybrid composite were mixed through a simple mixing method including a high energy sonicating and stirring on the hot plate in ethanol media until drying. Moreover, the h-BN/1 wt% CF composite was mixed with a similar method to compare the impacts of CNTs and GNPs addition on the mechanical properties and microstructure of the h-BN/CF composite. The high-temperature spark plasma sintering processes were performed at vacuum conditions of almost 2025 MPa with a starting pressure of 10 and a final applied pressure of 50 MPa at a maximum temperature of 1900 °C. Both prepared samples showed near full densification of higher than 98.1% of the theoretical density determined by Archimedes principle. Investigation of the crystalline phases by XRD represented only related peaks to h-BN. The FESEM images indicated an almost uniform distribution of reinforcement in the h-BN matrix. Furthermore, the polished surface of the provided samples showed only the pulled-out carbon fibers effects while the fracture surfaces confirmed the presence of CF and its tunneling effects. The obtained mechanical properties revealed 273±12 MPa of bending strength, 1.32±0.1 GPa of Vickers hardness, and 4.79±0.2 MPa.m0.5 fracture toughness for the prepared hybrid composite. 282 291 Hossein Eslami-Shahed Faculty of Materials and Manufacturing Technologies Malek Ashtar University of Technology, Tehran, 1491912354 Iran Khanali Nekouee Faculty of Materials and Manufacturing Technologies Malek Ashtar University of Technology, Tehran, 1491912354 Iran khnekouee@gmail.com Farhad Moravvej-Farshi Faculty of Materials and Manufacturing Technologies Malek Ashtar University of Technology, Tehran, 1491912354 Iran Fatemeh Dabir Non-Metallic Materials Research Group, Niroo Research Institute (NRI), Tehran, 14686-13113 Iran Hexagonal boron nitride CNTs Carbon fiber GNPs Spark plasma sintering Vol 4 No 4 Paper 5.pdf [1] D. Cai, Z. Yang, X. Duan, P. He, S. Wang, et al., Inhibiting crystallization mechanism of h-BN on ±-cordierite in BN-MAS composites, J. Eur. Ceram. 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