Fabrication And Sintering Features Of Nano-Ni/micro-TiB₂ Coated Particle By Hybridization

Cermet is a complex composite including metal or alloy and ceramic. It remains the special properties of ceramics, such as high strength, hardness, good wear and oxidization resistance, as well as the advantages of metal, such as good toughness and plasticity. Thus it attachs the interest of the researchers in composite. Titanium diboride (TiB₂) ceramics is a potential candidate for matrix of cermet because of its low density, high melting point, high hardness, thermal conductivity, electrical conductivity, good chemical stability and collision resistance. However the wetness between TiB₂ and most metal is not good, which makes it difficult to the densification process of TiB2-based cermet. Since nickel (Ni) is one of the several metals which have good wetness with TiB₂, how to prepare high density TiB₂-Ni cermet can greatly direct the fabrication and sintering of TiB2-based cermet.Hybridization (HYB) system is a novel powder surface modification equipment by high velocity gas flow, which was developed by Japan scientist Masumi Koishi and Hirotaka Honda in 1986. The raw powder can be immediately dispersed and impact blended by the high velocity rotor and gas flow. There are several strong actions between the raw powder particle involving strong impaction, compression, friction, shearing and collision, which make the fine particle coat on the core particle or make the raw powder sphericize in a short time. Many studies have revealed the possibility to create the coated structure of nano-particle onto the surface of micro-particle by hybridization.Based on the improvement of TiB₂-Ni cermet blended powder using conventional blended method, hybridization is used to fabricate nano-Ni/micro-TiB₂ coated particle with different conditions in this dissertation. The possibility of creating nano-Ni/micro-TiB₂ coated particle is approved by theoretical calculation and simulation. The effects of different conditions on the HYB process and the structure of HYB product are investigated, as well as the properties of the blended, coated and blended-coated powder. Finally, hot pressing (HP) sintering and Spark Plasma Sintering (SPS) method are used towards the blended and blended-coated powder, as well as the structure and properties of sintered product are reported.Theoretical calculation and simulation prove that the monolayer or multilayer coated structure can be formed when nano-Ni particle collide onto the surface of TiB₂ particle. The film structure will be easily formed and the thickness will decrease with...