Fabrication And Characteristics Of TiB₂-Oxide Multiphase Ceramics By Hot Pressing

TiB₂ exhibits high electrical conductivity,melting temperature and wear resistance,low specific weight and relatively good chemical stability,besides its extremely high hardness and elastic modulus.TiB₂ ceramics are very promising in modern industry.The main problems that limit the application of TiB₂ ceramics include:high fabrication cost,low sintering activity and inherent brittleness.Adding second ceramic phase,using sintering aids and optimizing fabrication technologies are believed important ways to improve its mechanical properties,sinterability of ceramics and cut down on costing.In this paper,TiB₂ ceramics were prepared by hot pressing technology,using Oxideâ… as the second phase,Oxideâ…¡as the sintering additive.The effects of Oxideâ… contents,Oxideâ…¡contents,sintering temperature and sintering parameter on structure and mechanical properties of TiB₂ ceramics were studied.The relationship between microstructure and mechanical properties was analyzed.The effects of Oxideâ…¡additive on the sintering process was also investigated.The factors of some phenomena in the sintering process were discussed as well.The sinter ability of TiB₂ ceramics were greatly improved when Oxideâ… was added as the second phase.The relative density of TiB₂- Oxideâ… multiphase ceramics reached above 96%with Oxideâ… content between 0%and 20%.These materials can also maintain eminent mechanical properties.In our research we can see that best integrated properties can be obtained with 15%Oxideâ… .Solide Solutionâ… (S I)can be obtained from reaction of Oxideâ… and Oxideâ…¡when Oxideâ…¡was added as the sintering additive.This phase can diffuse to holes between granules of TiB₂ and TiB₂ or TiB₂ and Oxideâ… under high temperature,which is good for densification of materials at some extent.The multiphase materials achieved most imaginable proerties with 3%Oxideâ…¡in our research.The mechanical properties was going to decrease when continuously increasing Oxideâ…¡contents.TiB₂- 15%Oxideâ… multiphase ceramics with 3%Oxideâ…¡was sintered under different temperature.The results showed that best mechanical properties can be acheved when the samles was sintered under 1600℃.When increasing the sintering temperature,properties of materials declined reversely,with grains grow obviously. The effects of hold time on microstructure and mechanical properties were studied at the same system.With 10 minutes of holding time,materials got high relative density and excellent mechanical properties.These means that the addition of second phase and sintering additive can greatly improve the sintering ability of TiB₂ ceramics.It can be densified quicky under relatively lower temperature.It was discovered in our research that Oxideâ…¡didn't react with Oxideâ… completely in forming S I when additive content was low.While 6%Oxideâ…¡was added,Oxideâ…¡completely reacted to form S I.We also found outflow of liquid phase and agglutination of sintering mould during sintering process.These phenomena should be attributed to oxide impurities and surface adsorption of oxygen,which can form eutectic phases with low melting points.They would flow out under temperature as low as 1600℃.