Enhanced toughness and hardness at cryogenic temperatures of silicon carbide sintered by SPS

The fracture behavior of silicon carbide (SiC) ceramics prepared by Spark plasma sintering (SPS) at cryogenic temperatures is firstly reported. The hardness of SiC increases from 31.2±1.54 to 38.3±1.62 GPa, especially, the fracture toughness also increases obviously from 6.6±0.37 to 7.3±0.45 MPa m1/2, with decreasing temperature from 293 K to 77 K. SiC samples have a interlock microstructure. And the Vickers indentation at 77 K has a larger dimple and laminate than that at 293 K. Moreover, the effect of residual stresses on the fracture mode and thus the toughness is discussed on the basis of theoretical analysis. The drawing and fracture process of glass phase at 293 K and 77 K are also simulated and analyzed by the molecular dynamics (MD) method.