Preparation And Properties Of Hot Pressed B₄C-based Composite With Layered Structure

B4C ceramic has the characteristics of light weight,super high hardness and high elastic modulus,and it is considered as one of the most ideal lightweight bulletproof armor materials.In 1960s,Materials scientists began to use boron carbide ceramics as bulletproof materials,and compared with other typical bullet proof ceramic materials,such as SiC,Al2O3,B4C ceramic has lower density and higher hardness.The boron carbide is suitable for armed helicopters and other aircraft to ensure the bullet proof performance of a high demand in special occasions,and has an irreplaceable role.But the low toughness of B4C ceramic material has been limited in the field of engineering and military applications.In the present study,the toughing methods of layered composite structure and second phase particles were used to improve the toughness of B4C.Ternary compound Ti3SiC2 with good high temperature strength and plasticity and/or Si phases were added in B4C matrix as the toughening layers.B4C-B4C/synthesized Ti3SiC2 composites with different components,and B4C based three-layer composite materials of B4CB4C/40%Ti3SiC2-B4C/10%Si and B4C/10%Si-B4C/40%Ti3SiC2-B4C/10%Si were prepared by hot pressing method.The density,phase composition,microstructures,mechanical properties and strengthening and toughening mechanism of the layered composite materials were investigated in detail.For the first group of B4C two-layer composite material,3.Owt.%C and 2.5wt.%Ti powder were added in to B4C as a ceramic layer.While the B4C(1?m),SiC,Si,Ti,TiC and Al powders were added in the B4C ductile layer in order to synthesize the ternary Ti3SiC2 phase.For the second group of B4C three-layer composite materials,B4C ceramic layer was the same as that in the B4C two-layer composite material,while 40wt.%Ti3SiC2 and 10wt.%Si powders were directly add into the B4C matrix as the B4C/40%Ti3SiC2 layer and B4C/10%Si layer,respectively.The experimental results were shown as follows.(1)For the B4C-B4C/synthesized Ti3SiC2 two-layer composites,the flexural strength and fracture toughness increased with the increase of the additions of this layer.The best performance of B4C two-layer composite is the specimen of with 40%Ti3SiC2 in the ductile layer,the hardness of the ceramic layer and ductile layer,flexural strength and fracture toughness were 30GPa,31GPa,550MPa and 6.6MPa·m1/2,respectively.(2)SEM fracture morphology of B4C-B4C/synthesized Ti3SiC2 composites showed that the B4C layer was mainly a transgranular fracture mode,and the proportion of intergranular fracture increased with increasing the amount of additions in the ductile layer.(3)For the B4C three-layer composites the comprehensive properties of B4C/10%SiB4C/40%Ti3SiC2-B4C/10%Si was the better one of which the hardness of all these three layers were higher than 30GPa,meanwhile the flexural strength and fracture toughness were 490MPa and 4.8MPa·m1/2,respectively.(4)Observed from the SEM fracture morphology,it was clear that both the B4C and B4C/10%Si layers were mainly a transgranular fracture,and the B4C/Ti3SiC2 layer is a mixed mode of intergranular fracture and intergranular fracture.