The Preparation Of B₄C Matrix Composites By The Method Of Reaction Sintering

The B₄C matrix multiphase ceramics have been fabricated by pressureless infiltration of B₄C-C or B₄C preforms with molten Si and Al under an argon protective atmosphere at a low temperature.The B₄C-C or B₄C preforms were re-pressd by cold isostatic pressing?CIP?after die molding pressing to improve their performance.The influence of compact process on the properties of the preforms was studied.OM,SEM,XRD were used for exploring material's microstructure and phase composition.The mechanical property was tested by three points bend experiment.The relationship between organization structure and mechanical property was discussed.The following conclusions are reported in this paper.1)The density of the porous preforms compacted by steel mould exhibt a linear relationship with moulding cycle.Adjusting the proportion of coarse and fine powders can improve the density of the preforms.The porous preforms'density achieves the maximum when F500 content reaches to 25%.When the molding pressure reaches to 120MPa,it achieves maximum density of 1.9g/cm³.2)The CIP process can improve the uniformity of the porous preforms.Their density and strength increase with the increase of pressure.But the density and strength growth trend gradually decrease,and the value of density and strength tends to be constant at a level of 1.96g/cm³ and 2 MPa when the pressure reaches to 150 MPa.The dwelling time has little influence on the prefabricated body performance.The difference between maximum and minimum value of strength is about 0.05 MPa.3)The B₄C/SiC/Si composite made from the perform with content of 7%carbon exhibit good mechanical properties,the hardness and bending strength of which are 2684 kg/cm² and 241 MPa,respectively.It is found that B₄C,B₁₂(B,C,Si3),Si and?-SiC phases are existed in the composite.Different morphological?-SiC can be observed in the composites by optical microscopy.Increasing the volume fraction of boron carbide and?-SiC,reducing the content of residual silicon in the composites will enhance their bulletproof performance.4)It is found that B₄C?Al?Al₃BC?AlB₂ and Al₄C₃ phases are existed in B₄C/Al composite.Materials sintered at the temperature of 1300?exhibit good performance.The value of bend strength is 270MPa and the value of fracture toughness is 3.2MPa·m^1/2.With the increasing of sintering temperature,the phase content of AlB₂ decrease,Al₄C₃ increases slightly,and Al₃BC increases firstly and then decrease.Al₄C₃ generated as a harmful phase in the sintering process.