In this paper, 3mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and TiN/3Y-TZP(adding TiN particles to 3Y-TZP) composites were fabricated by hot-pressing technique. Phase composition, microstructure and mechanical properties of the composites were investigated. It is shown that the flexural strength, fracture toughness and Vickers hardness of TiN/3Y-TZP was significantly improved by the addition of TiN particles compared with 3Y-TZP. The flexural strength of ZYT2 (20wt% TiN addition) is 1318 MPa. The fracture toughness of ZYT4 (40wt% TiN addition) is 16.8MPa·m1/2. The toughening and strengthening mechanisms were analyzed. The XRD results show that the additing of TiN can hinder the transformation from tetragonal phase to monoclinic phase of 3Y-TZP during fabrication process.

An advanced self-toughening silicon nitride ceramic tool YL16A has been developed by adding proper additive Y 2 O 3 -La 2 O 3 into the phase silicon nitride and using the hot press fabrication technology. It is found from a scanning electron microscope (SEM) observation that the self-toughening mechanisms of the new ceramic tool material are columnar grain bridge and pullout similar as the whisker reinforcing mechanisms. Some -Si 3 N 4 grains are converted into columnar -Si 3 N 4 grains with a high aspect ratio, and improve the fracture toughness of the new silicon nitride ceramic tool. The tests of mechanical properties, and wear and fracture resistance in machining are finally conducted. It is shown that the wear resistance of YL16A is almost the same as that of a commercially available alumina matrix ceramic tool SG4 and the fracture resistance of YL16A is markedly stronger than that of SG4. The new self-toughening ceramic tool YL16A can increase the tool-life by fracture by about 388% as compared to SG4 when intermittent cutting a quenched mild carbon steel. While the fracture toughness of the new ceramic tool is improved by up to 112-130% compared with other two general ceramic tool materials.

Advanced Ti(C, N) matrix cermet tool materials with higher mechanical properties are successfully developed by dispersing nano-scale Al2O3 powder into the micro-scale Ti(C, N) matrix and Ni-Mo bonding phases powder. The effect of the content of nano-scale alumina on the microstructure and mechanical properties of micro-scale Ti(C, N) matrix cermet tool materials are investigated. The research results show that a type of Ti(C, N) matrix cermet tool material has the most optimal flexural strength of 900MPa, Vickers hardness of 17.4GPa and fracture toughness of 9.95MPa.m1/2 when the content of nano-scale alumina is 12% in term of mass. It is found from the microstructure analysis that the main reason of the mechanical properties improvement is the grain fining effect caused by nano-scale Al2O3.

The effect of sintering temperature on mechanical properties and microstructure of rare earth oxides toughened Ti(C,N) ceramic cutting tool materials was investigated. The results showed that the mechanical properties of Ti(C,N) based ceramics were greatly influenced by sintering temperature. As a result, both of the density and mechanical properties of the materials sintered at 1350 and 1400 are worse than those sintered at 1450 and 1500. Low sintering temperature results in low density and degraded mechanical properties, but too high sintering temperature results in the precipitation of bond metal and thus reduces its fracture toughness. Intergranular fracture mode of the material is mainly observed.

Ti(C, N)-Mo 2 C-Cr 3 C 2 system cermet with a low content of Mo 2 C and Cr 3 C 2 was fabricated by hot pressure technology. The mechanical properties and SEM microphotography of fracture surface and indention crack propagating on ground surface of the Ti(C,N) based cermet were discussed. It is shown that the fracture modes of the fabricated materials are mainly intergranular fracture, the flexural strength of the materials is closely related to the thickness of Rim phase, and the cermet with a content of 8wt.% Mo 2 C has high flexure strength owing to moderate thickness of Rim phase. It is also demonstrated that the cermet with a content of 1.6wt.% Mo 2 C possesses high fracture toughness due to shorter crack path, crack deflection and crack branches. It was found that the flexure strength increases with the content of Cr 3 C 2 . The cracks exist on the interface between Cr 3 C 2 and Ti(C,N) due to tensile stress and result in a decrease of crack propagating resistance, thus the fracture toughness of the cermet deeply decreases with the increase of Cr 3 C 2 content when Cr 3 C 2 content is more than 8wt.%.