Fabrication and mechanical properties of TiN/ZrO_2(2Y) composites by hot isostatic pressing

摘要

Titanium nitride (TiN), being an intermetallic compound, is used as a component of highly refractory cermets employed in the melting of metals and also as a component of superhard cutting tools. The most common fabrication methods for producing dense TiN ceramics are conventional sintering and hot pressing in the presence of additives such as Co or Ni metal [1,2]. The additives play an important role in promoting densification but cause the precipitation of second phase at grain boundaries. Yamada et al. [3,4] fabricated pure dense TiN ceramics by high pressure hot pressing and hot isostatic pressing, and evaluated their microstruc-tures, thermal conductivities and Vickers hardness. Themelinm and Boncobva [5] studied the densification of pure TiN powder and reported that the fracture toughness and bending strength of hot isostatically pressed (1600 ℃/180 MPa) TiN ceramics (99.3% of theoretical) were 5MPam~(1/2) and 550 MPa, respectively. On the other hand, the fracture toughness of chemical vapour deposited (CVD) TiN films was determined to be 3.7 MPam~(1/2) [6]. The main difficulty with this material, like almost all intermetallics, is an inherent lack of toughness. It cannot therefore be employed by itself as a structural material. This material needs to be reinforced in order to improve the mechanical properties. Transformation toughening has been shown to be a very important toughening mechanism in ZrO_2-based materials. A very attractive reinforcing species for TiN is ZrO_2, due to its potential for toughening and strengthening, and the fact that its thermal expansion coefficient is a good match to that of TiN [7], In the present study, hot isostatic pressing was adopted to fabricate dense TiN/ZrO_2(2Y) composites. As a result, the room temperature toughness of the composites was ~3 times tougher than that of pure TiN. This letter deals with the sintering, microstructures and mechanical properties of ZrO2(2Y) particle-TiN matrix composites.