Study On Synthesis And Sintering Properties Of TiB₂ Powders Based On Three Different Solid-state Reduction Methods

Titanium diboride?TiB₂?have received considerable attention as cutting tools,lightweight armor and wear-resistant materials,due to excellent properties of high hardness,high strength and good wear resistance.At present,the researchers were looking for appropriate sintering process and additives to improve the properties of TiB₂ ceramics.However,the characteristic of TiB₂ powders?particle size and impurity content?also affected the sintering and properties of ceramics.Therefore,in this paper,TiB₂ powders were synthesized by three solid-phase reduction methods,including borothermal reduction,B₄C reduction and boro/carbothermal reduction.Then three kinds of synthesized TiB₂powders were used as raw materials,and Ni and SiC were used as sintering aids to prepare TiB₂-based ceramics by hot pressing.The effects of powder characteristics on densification,microstructure,and mechanical properties of Ti B₂-based ceramics were studied.First of all,three kinds of TiB₂ powders were synthesized by borothermal reduction,B₄C reduction and boro/carbothermal reduction using TiO₂,B,B₄C and C as the raw materials.The mechanism of three different solid-phase reduction methods and the synthesized Ti B₂ powders were compared.The results showed that the main TiB₂ phase was formed at 1000? by borothermal reduction method,the main TiB₂ phase was formed at1100? by B₄C reduction method,and the main TiB₂ phase was formed at 1300? by boro/carbothermal reduction method.The TiB₂ powders synthesized by the borothermal reduction method have the highest oxygen content?1.37%?and the finest grain size?0.39?m?,while the TiB₂ powders synthesized by the boro/carbothermal reduction method have the lowest oxygen content?0.83%?and the biggest grain size?0.87?m?.Then TiB₂ ceramics were prepared by hot pressing at 1800? using three kinds of self-synthesized TiB₂ powders as raw materials and Ni as sintering aid,and the densification,microstructures and mechanical properties were studied.The results revealed that the TiB₂powders prepared by B₄C reduction method have best sintering properties,and the relative density after hot-pressing was 93.7%.The TiB₂ grains of ceramics using by three kinds of TiB₂ powders synthesized by the borothermal reduction,B₄C reduction and boro/carbothermal reduction all exhibit rod-like structure and partial texturing.The grain sizes of TiB₂ were 25.3?m,7.5?m and 32.4?m,respectively.Using TiB₂ powders synthesized by B₄C reduction,the TiB₂ ceramics has relatively good mechanical properties,and its hardness,flexural strength and fracture toughness were 18.6±2.1GPa,416.7±10.9MPa and 6.72±0.08MPa?m^1/2,respectively.Finally,in order to further improve the relative density of TiB₂-based ceramics and refine its grains,SiC was introduced as second phase.The effects of the TiB₂ powders synthesized by three different methods on the densification,microstructures and mechanical properties of hot-pressed TiB₂-SiC ceramics were studied.The results indicated that the TiB₂-SiC ceramics were fully densified using TiB₂ powders synthesized by borothermal reduction,B₄C reduction and boro/carbothermal reduction as raw materials.The relative densities of Ti B₂-SiC composites were 99.9%,98.7%and 99.5%,respectively.Three kinds of Ti B₂-SiC ceramics have similar TiB₂ grain size of 2?m.Compared with the addition of Ni,SiC significantly improved relative densities and refined grains of TiB₂-based ceramics.he hardness of three kinds of TiB₂-SiC ceramics were 25.1±1.1GPa,26.5±1.2Ga and26.1±1.8GPa,respectively.Using Ti B₂ powders synthesized by borothermal reduction and boro/carbothermal reduction,TiB₂-SiC ceramics have relatively better flexural strength and fracture toughness.The flexural strength values were 747.1±60.5MP and 750.3±87.4MPa,respectively,andfracturetoughnessvalueswere10.53±0.90MPa?m¹/2/2 and10.24±1.83MPa?m^1/2,respectively.