Preparation And Properties Of Boron Carbide （B₄C） Composite Ceramics

The third hardest material known to man,black diamond,B₄C ceramic,is an attractive ceramic because of its excellent properties such as low density,high melting point,high hardness,outstanding chemical stability and excellent absorption neutron cross-section.It has many applications,such as abrasive cutting,as a coating material,for light-weight armour and for controlling nuclear fission.B₄C ceramic also has high Young’s modulus and low fracture toughness.Due to these characteristics,B₄C ceramic is too difficult to sinter.In this paper,boron carbide ceramic composites were sintered and prepared by two technical methods,namely spark plasma sintering（SPS）method and high temperature and high pressure（HPHT）method,in order to improve their mechanical and electrical properties.The main conclusions of the study are as follows:（1）Preparation and properties of Boron carbide composite materials prepared by spark plasma sinteringBy doping titanium hydride（Ti H₂）into boron carbide（B₄C）,a series of B₄C+X wt%Ti H₂（x=0,5,10,15 and 20）composite ceramics were obtained through spark plasma sintering（SPS）.The effects of sintering temperature and the amount of Ti H₂ additive on the microstructure,mechanical and electrical properties of the sintered B₄C-Ti B₂ composite ceramics were investigated.Powder mixtures of B₄C with 0-20wt%Ti H₂ were heated from 1400 to 1800°C for 20 minutes under 50 MPa.The results indicated that higher sintering temperatures contributed to greater ceramic density.With increasing Ti H₂content,titanium diboride（Ti B₂）formed between the Ti H₂ and B₄C matrix.This effectively improved Young’s modulus and fracture toughness of the composite ceramics,significantly improving their electrical properties:the electrical conductivity reached 114.9 S/cm at 1800°C when x=20.Optimum mechanical properties were obtained for the B₄C ceramics sintered with 20 wt%Ti H₂,which had a relative density of 99.9±0.1%,Vickers hardness of 31.8 GPa and fracture toughness of 8.5 MPa·m^1/2.（2）Preparation and properties of Boron carbide composite materials prepared by high temperature and high pressureBy doping diamond into boron carbide（B₄C）,a series of B₄C+Y vol%diamond（Y=0,10,20）composite ceramics were obtained through high temperature and high pressure（HPHT）.The effects of sintering temperature and the amount of Diamond additive on the microstructure,mechanical and electrical properties of the sintered B₄C-Diamond composite ceramics were investigated.Powder mixtures of B₄C with 0-20vol%diamond were heated from 1200 to 1600°C for 10 minutes under 5 GPa.The results indicated that higher sintering temperatures contributed to greater ceramic density.With increasing diamond content,the Young’s modulus,fracture toughness and electrical properties of the composite ceramics significantly improved:Optimum mechanical properties were obtained for the B₄C ceramics sintered with 20 vol%Diamond,which had a relative density of 99.9±0.1%,Vickers hardness of 41.2 GPa.The electrical conductivity reached 7.0 S/cm at 1400°C when Y=20,and fracture toughness of 29.2 MPa·m^1/2 at 1600°C when Y=10.