The effects of oxide additions on the microstructure and R-curve behavior of in-situ reinforced silicon nitride

Abstract

The B4C/BN ceramics composites were fabricated by the hot-pressing process. In this paper, the mechanical property and R-curves behavior of the B4C/BN composites were investigated. The fracture strength and fracture toughness of the B4C/BN microcomposites and the B4C/BN nanocomposites decreased gradually with the increasing content of h-BN. The fracture strength and fracture toughness of the B4C/BN nanocomposites were significantly improved in comparison with the B4C/BN microcomposites. The damage resistance and R-curves behavior of the B4C monolith and the B4C/BN composites were evaluated by the indentation-strength in bending technique (ISB). The fracture strength of the B4C monolith, the B4C/BN microcomposites and the B4C/BN nanocomposites decreased gradually with the increase of the indentation load. The B4C/BN nanocomposites retained relative higher fracture strength in comparison with the B4C monolith and the B4C/BN microcomposites under the equivalent indentation load. The B4C monolith, the B4C/BN microcomposites and the B4C/BN nanocomposites all exhibited the rising R-curves behavior. The B4C/BN nanocomposites exhibited the higher rising R-curve behavior than that of the B4C monolith and the B4C/BN microcomposites. The toughness mechanisms of the composites were investigated. The B4C/BN composites with the h-BN content more than 20 wt.% exhibited excellent machinability. The slowly rising R-curves behavior remarkably improved the machinability of the composites.