High-temperature spark plasma sintering of h-BN composites reinforced with carbon nanotubes, carbon fibers, and graphene nanoplates

Abstract

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, h-BN/1 Wt. % CF composite was mixed with a similar method to compare impacts of CNTs and GNPs addition on the mechanical properties and microstructure of h-BN/CF composite. The high-temperature spark plasma sintering processes were performed at vacuum conditions of almost 20-25 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 it’s 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.m^0.5 fracture toughness for the prepared hybrid composite.