Microstructure And Mechanical Properties Of TiB₂ Ceramics With Borides As Sintering Additives

TiB₂ ceramics have excellent physical-chemical properties and mechanical properties, which show promising application in modern industry. In this paper, NbB₂ and VB were selected as secondary phases for TiB₂. TiB₂ based composites with addition of NbB₂ and VB were prepared by hot-pressing. The mechanical properties and microstructure of these composites were studied.Improved mechanical properties of TiB₂ composites with NbB₂, especially high flexural strength, can be gained compared to those of pure TiB₂. Samples of TiB₂-6mol%NbB₂ hot-pressed at 1750℃for 2h gains the maxium flexural strength of 850±20MPa, Vickers hardness of 21.15±0.15GPa, fracture toughness of 5.35±0.1 MPa·m^1/2.NbB₂ and TiB₂ reacted to form solid solution (NbTi)B4 during hot-pressing, which dispersed in TiB₂ matrix. It was found that the addition agent hindered the grain growth of TiB₂. The composites exhibited a fracture surface which indicated both transgranular fracture mode and intergranular fracture mode, while pure TiB₂ only showed an intergranular fracture mode. Complicated dislocations structure dispersed in TiB₂ grain, which is beneficial to enhance the mechanical properties.Mechanical properties of samples with VB were also improved than of pure TiB₂. Samples of TiB₂-8mol%VB hot-pressed at 1800℃for 1h had maxium mechanical properties than samples under other sintering conditions. The specimen sintered at this condition has 20.44±0.5GPa for Vickers hardness, 767±19MPa for bending strength and 5.23±0.07MPa·m^1/2 for fracture toughness.VB and TiB₂ reacted to form solid solution, which dispersed in TiB₂ matrix. It was found that the VB hindered the grain growth of TiB₂ during sintering. The composite exhibited a flat fracture surface which indicated both transgranular fracture mode and intergranular fracture mode.