Investigation of the effects of varying amount of graphene nanoplatelets’ (GNPs) addition on carbon nanotubes (CNTs) reinforced boron carbide produced by spark plasma sintering

Abstract

In this study, monolithic B4C, B4C-CNT, B4C-GNP, and B4C-CNT-GNP composites were prepared by ultrasonic stirrer with the additions of 3.5 vol.% carbon nanotubes (CNTs) and 0–3 vol.% graphene nanoplatelets (GNPs) and produced by spark plasma sintering (SPS) method. Samples are produced at 1600–1650 ℃ sintering temperatures under 40 MPa for 5-min holding time. The effects of GNP addition on the densification behavior, microstructure, and mechanical properties of B4C-CNTs composites were investigated. The sintering temperature was reduced from 1650 to 1600 °C with the addition of CNTs and GNPs separately. Sintering temperature was also 1600 °C for the all B4C-CNT-GNP composites. The relative density value was 96%, 97.2%, and 98.4% for the monolithic B4C, B4C-CNT and B4C-GNP composites, respectively. The highest relative density value was obtained as a 97.9% by B4C-CNT-GNP composites. The hardness value was 30 GPa, 32.1 GPa, and 35.4 GPa for the monolithic B4C, B4C-CNT and B4C-GNP composites, respectively. The highest hardness value was 32.3 GPa for B4C-CNT-GNP composites. There was an increase in fracture toughness of B4C-CNT composites with the addition of the GNP up to 2 vol.%. The highest fracture toughness was obtained as 6.20 MPa‧m1/2 for the sample containing 2 vol.% GNP. Increase in fracture toughness resulted from the pull-out of GNPs, bridging the cracks and changing the direction of the cracks by GNPs.