Preparation And Mechanical Properties Of TiB₂-B₄C Composite Ceramics

Boron carbide possesses numerous outstanding characteristics,such as low density,high melting point,high hardness,high neutron absorption ability and good thermoelectric properties.By virtue of its prominence,boron carbide has been widely used in the area of protect armor,engineering structure,wear-resistant components,unclear industry as well as the electric power engineering.However,the covalent bond proportion of B₄C is as high as93.94%,which makes the B₄C ceramics very difficult to be densified and possess a low fracture toughness.These two short points made it even harder to prepare the B₄C ceramics that both have the high density and possess the excellent mechanical properties.As a result,the extensively use of boron carbide ceramics is severely limited on the field of engineer and military industry.In order to optimize the sintering process and improve the mechanical properties of boron carbide ceramics,we chose to prepare the TiB₂-B₄C composite ceramics by adding metal titanium powder into the raw material.This process was conducted with the method of hot-pressing sintering.Then,the relative density together with the XRD phase analysis,microstructure,Rockwell hardness,bending strength and the fracture toughness of the specimen were investigated.Firstly,two kinds of reaction systems were designed.One is the B₄C-Ti-Al-B₂O₃-C system and the other is the B₄C-Ti system.And then a thermodynamic analysis of both of the two systems was carried out.According to this result,whether all of the possible reactions can be easily happen was explored.In the meantime,the possible phases that may exist under the equilibrium state were analyzed in theory.Secondly,with the B₄C,Ti,Al,B₂O₃ and C powder as raw material,three kinds of raw material ratio were designed.The TiB₂ content of the TiB₂-B₄C composite ceramics in the three ratios were 10.5 wt.%,17.5 wt.%and 24.5 wt.%respectively.Then the powder were sintered at the temperature of 1800℃,1850℃and 1900℃separately.The purpose of this investigate was to explore the influence of sintering temperature and raw material ratio on the mechanical properties of TiB₂-B₄C composite ceramics.Ignoring the influence of raw material ratio,the specimen which was sintered in 1900℃achieved the best performance.And among all the three kinds of specimen that sintered at the temperature of 1900℃,the second specimen that with 17.5wt.%TiB₂ obtained the best comprehensive performance.The relative density was 99.6%when the TiB₂ was 17.5wt.%.And to the same specimen,the Rockwell hardness was 93.5 HRA,the bending strength was 419 MPa and the fracture toughness was 5.675 MPa·m^1/2,which increased 158%compared with the pure B₄C ceramics.Thirdly,with the B₄C and Ti powder as raw material,five kinds of raw material ratios were designed.The content of titanium was 10wt.%,20wt.%,30wt.%,40wt.%and 50wt.%respectively.Firstly,the powder which has 40wt.%Ti was chosen as the raw material.And then it was sintered at the temperature of 1750℃,1800℃,1850℃and 1900℃respectively.Then analyzing the test results of all the specimen,we can get that the best sintering temperature of this series was 1900℃.Secondly,the powder of all the five kinds of material ratio were sintered at the temperature of 1900℃and the subsequent tests were conducted.Finally it was concluded that when the Ti content was 40wt.%,the sintered body could achieve the best comprehensive performance.The relative density was 97.18%when the Ti was 40wt.%.And to the same specimen,the Rockwell hardness was89.43HRA,the bending strength was 552.132 MPa and the fracture toughness was 5.6012MPa·m^1/2,which increased 155%compared with the pure B₄C ceramics.