Preparation And Mechanical Properties Of TiB₂-Fe-Ni-Al Cermet

TiB₂ ceramics have excellent physical-chemical properties and mechanical properties. Apart from its extremely high hardness and elastic modulus, TiB₂ exhibits high electrical conductivity; melting temperature and wear resistance, low specific weight and relatively good chemical stability. TiB₂ ceramics are very promising in modern industry. The main problems that limit the application of TiB₂ ceramics include: high price of TiB₂ raw materials, low sintering activity and the inherent brittleness. Adding of metal is an important way to improve the mechanical properties of ceramics. In this paper, liquid phase sintering of T1B2 ceramics with the additions of Fe-Ni-Al as binder phases was attempted by hot pressing technology. The effects of metal content, sintering temperature and pressure modes on mechanical properties of TiB₂ materials were studied, the relationship between microstructure and mechanical properties was analyzed, and the sintering mechanism was also discussed.The microstructure and mechanical properties of ceramics were significantly influenced by sintering aids content and composite. The sintering temperature decreased with the increasing of metal contents, which could improve the mechanical properties of ceramics. The mechanical properties of ceramics were also influenced by sintering aids composite. With the increasing of Al as sintering additive, the relative density, Rockwell hardness and bending strength of compacts increased to the maximum and then decreased. With the changes of metal contents, the material that has 2vol% Fe-Ni-Al showed excellent mechanical properties (Rockwell hardnesss: 92.9HRA, bending strength: 711MPa).Sintering temperature influenced hot-pressing process. With certain Fe-Ni-Al content (7vol% and 10vol% metal content), Rockwell hardness and bending strength of compacts increased and then decreased with the sintering temperature. Peaks appeared at 1550℃. Experimental results showed that TiB₂ ceramics which had7vol% Fe-Ni-Al (Fe: Ni: Al=3: 1: 3) by hot pressing at 1550°C and 30MPa for 60 min in Ar had high Rockwell hardness and bending strength (HRA: 92.6, bending strength: 659MPa).Sintering pressure was an important parameter in hot-pressing process. Effect of pressing modes on mechanical properties of TiB₂ materials was studied. Experimental results showed that when ladder-pressing model (pressure became 30MPa in 5 min before temperature would be appointed sintering temperature) was selected, the material that had 3vol% Fe-Ni-Al shows good mechanical properties (Rockwell hardness: 92.7HRA, bending strength: 689MPa).The study on microstructure showed that: As a whole, the particle size was as large as each other. However, some big sintered TiB₂ particles existed in some parts of the specimen. The metal liquid dispersed symmetrically in the sintered compact, which on grain-boundary. Al element had been oxidized, which distributed in boundary. The reactions of Fe and Ni with TiB₂ are not controlled because of Al oxidation and form of metallic boride of the M2B type, which were even more brittle than titanium diboride and had a bad like wetting property. Furthermore, some impurity phases distribute in trigonal grain-boundary, they involved mostly TiO₂, TiC, which possibly influence the mechanical properties of TiB₂ ceramics.Study on the sintering mechanism showed that: in initial stage of sintering, the main mechanism of densification was the re-arranging of material powder. In meta-and late-stage of sintering, the mechanism of densification was the diffusion through grain boundary. The effect of late-stage of sintering on the densification was inconspicuous, which is mainly the adjustment of grain shape and boundary.