Study On TiB₂ Ceramics By Hot-Pressing

TiB₂ is of burgeoning interest,principally because such material has good physicochemical properties,i.e.high electrical conductivity,melting temperature, wear resistance,low specific weight and relatively good chemical stability,but extremely high hardness and elastic modulus also limit its practical applications.Like other non-oxides ceramics,high temperature(more than 2000℃) and hot pressing are necessary to be used to densify TiB₂ ceramics because of the strong B-B covalent bond and low self-diffusion coefficient of B atoms.In order to decrease the sintering temperature of TiB₂ ceramics,additives are usually needed.The study mostly focused on the effect of the additives on densification and microstructure of TiB₂ in the previous research.On the other hand,the addition of additives also would cause the degradation of mechanical properties and oxidation resistance at elevated temperature.In this paper,TiB₂ ceramics were prepared by hot pressing technology,with the different sintering additives,not only improve the density,but also avoid other impurities generating.The hot sintering theories and the effects to partical size, oxygen were also studied.According to the study status,all the research contents and results are as follows:Firstly,TiB₂ ceramic was fabricated by hot pressing with B₄C or C,which can react with TiO₂,B₂O₃ to improve the sintering,the samples were densified in 2000℃. The obstruction mechanism of oxygen content on the sintering and the role of sintering agent were also analyzed.The XRD,SEM analysis showed that C is more suitable than B₄C as an additive on sintering TiB₂,the reaction of B₄C with TiO₂ would generate B₂O₃,which cause the residual of B₂O₃,and then making the exception grow grain,while the C can react with B₂O₃,get more uniform grain structure. Secondly,this paper focused on the in-situ reaction sintering aids in TiB₂ hot sintering.With Ti/B,Ti/B₄C and Ti/C composite add as the sintering aids,the use of sintering additives in-situ reaction between the sintering activity with a good second-phase particles to promote the sintering TiB₂ ceramics and obtained relative density greater than 97%of TiB₂ ceramics,more significantly,the second phase of this approach generated(titanium diboride or titanium carbide) has a high melting point as the matrix,and will not be guaranteed high-temperature mechanical properties of the material adverse impact.The successful implementation of the subject will be useful to the borides structural ceramics,particularly to research and application of TiB₂ ceramics.Thirdly,the additives used in the thesis not only promoted the densification of TiB₂ sintered,but also inhibit grain growth.Articles by milling off TiB₂ done by adding C additive,was found significantly reduced grain.