Preparation And Properties Of B₄C–TiB₂ Composite Ceramics

Boron carbide?B₄C?is one of the high performance ceramic materials with potential application and development prospects.However,it is difficult for the properties of monolithic B₄C ceramic to satisfy the need of actural application.Titanium diboride?TiB₂?has properties similar to those of B₄C,the combination of B₄C with TiB₂ to form B₄C?TiB₂ composites not only improves the sinterability but also refines the microstructure and enhances the mechanical properties of the material.Moreover,due to the excellent conductive property of TiB₂,the addition of TiB₂ into B₄C matrix decreases the electrical resisitance of the material to meet the requirement of electrical discharge machining.Therefore,B4C-TiB2 has become one of the most potential composites.In this thesis,the focus is on the preparation and properties of B₄C?TiB₂composites.The major works and results are summarized as follows:Firstly,B₄C–30 vol.%TiB₂ composites were prepared by hot pressing sintering with B₄C and TiB₂ powder as raw materials,and the effects of B₄C particle size on the densification,microstructure and mechanical properties of composites were investigated.The results showed that fully dense B₄C–Ti B₂ composites could be obtained by sintering at2000 ^oC/35 MPa for 1 h.The B₄C particle size had little effect on the mechanical properties of the composites.The flexural strength,hadness and the fracture toughness of the obtained B₄C?TiB₂ composites was 689?754 MPa,29.15?30.42 GPa and 4.26?5.23 MPa·m^1/2,respectively.Secondly,B₄C–41 vol.%TiB₂ composites were prepared by reactive hot pressing sintering at 2000 ^oC/35 MPa for 1 h using TiC and amorphous B powder as raw materials,and the effects of batching,TiC particle size on the densification,microstructure and mechanical properties of composites were investigated.The results indicated that the excess of 10%B could eliminate the carbon produced at the sinteing process.With increasing B content,boron carbide with richer B than B₄C was produced and affected the density&mechanical properties of the composites.When the raw TiC powder was microsize and the excessive B increased from 10%to 30%,the flexural strength of the composites declined from 659 MPa to 512 MPa,while the Vickers hadness and the fracture toughness of the composite enhanced from 26.7 GP and 4.53 MPa·m¹/2/2 to 30.4 GPa and 5.78 MPa·m^1/2,respectively.The TiC particle size had significant effects on the composites.When the TiC particle size was too fine,it was easier to be oxidized and the produced oxides prohibited the densification of the composite.When the TiC particle size was too coarse,the obtained composites had coarse microstructures.When the B was 10%excessive,the composite obtained from 0.8?m Ti C powder had the highest flexural strength of 569 MPa.Finally,B4C–41 vol.%TiB2 composites were prepared by reactive pulse electrical current sintering at 1900 ^oC/50 MPa using microsize TiC and amorphous B powder as raw materials,and the effects of holding time before and after applying pressure on the densification,microstructure and mechanical properties of composites were investigated.The results revealed that 1 min hoding time before applying pressure degassed the B2O3 during the sintering process,which improved the densification of the composites.When the holding time after applying pressure was 4-10 min,the density of the composite increased with increasing holding time,the flexural strength enhanced from 492 MPa to 640 MPa,and there was little change on the fracture toughness and the hardness.