Polycrystalline zirconia material modified By means of the TiC inclusions synthesized IN SITU
Waldemar Pyda Akademia Górniczo-Hutnicza, Wydział Inżynierii Materiałowej i Ceramiki, al. Mickiewicza 30, 30-079 Kraków
Annals 3 No. 7, 2003 pages 151-158
DOI:
keywords:
abstract The reaction between carbon and titanium originated from zirconia s.s. was used to produce TiC inclusions in situ in zirconia dense materials. The co-precipitated powder composed of 1.5 mol% Y2O3, 18 mol% TiO2 and 80.5 mol% ZrO2 and its mixture with phenol-formaldehyde resin was used. The cold pressed green bodies were pressurelessly sintered for 2 hrs at the temperatures ranging from 1000 to 1500oC in argon. A carbon bed was used to carburise surface of the bodies during sintering. The formation of TiC led to destabilisation of the zirconia solid solution due to the oxygen vacancy consumption. As a result, the cubic form of the zirconia solid solution transformed to the tetragonal one, which further transformed to the monoclinic form during cooling. TiC formed in situ was the nonstoichiometric phase which contained most probably oxygen in its structure. It appeared as inter- and intragranular inclusions in the zirconia solid solution matrix. A size of the TiC inclusion ranged from nano- to micrometric depending on the preparation conditions. The TiC formation reduced a size of the zirconia solid solution grains and improved mechanical properties of the zirconia material. Carburising of the green body during sintering led to the formation of the layer with an increased TiC concentration and therefore increased hardness. Carbon introduced to the system before sintering controlled the layer thickness. A temperature of 1000oC has been found to be the lowest at which the TiC formation proceeded. The samples heated at 1500oC showed the presence of ZrC in their surface. Key words: composites, ZrO2, carbides, inclusions, solid state reaction