Abstract:
Tetragonal zirconia is known as ‘ceramic steel’ due to its excellent hardness and fracture
toughness. However, at low temperatures (< 300 C) and in the presences of hydroxyls,
tetragonal zirconia transforms into monoclinic zirconia which leads to property degradation,
a phenomenon known as low temperature degradation or hydrothermal ageing. This ageing
hinders the wide-spread use of zirconia in biomedical applications. Amongst the strategies
used to enhance the ageing resistant of zirconia, two-step sintering (TSS) is a promising
approach to achieve high densification and finer grain size. In this study, TSS method was
used to sinter 3 mol% yttria stabilized tetragonal zirconia polycrystalline (3Y-TZP) ceramic.
Zirconia powder was uniaxial pressed followed by cold isostatic pressing and sintered at
different TSS profiles. The samples were initially heated to first step sintering temperature
(T1) and held at that temperature for one minute and then cool down to a second step sintering
temperature (T2) and held at the second step sintering temperature for 5 hours (T1/T2).
Hydrothermal ageing was conducted for 36 hours in an autoclave containing superheated
steam at 180 C and 10 bar pressure. Phase transformation was analyzed by using the XRD
method. The figure shows the effect of ageing time and different sintering profiles on the
ageing-induced monoclinic development in the ceramics. It was revealed that as the sintering
temperature increased, this was accompanied by an increase in the monoclinic content. The
monoclinic phase development trends for samples sintered using with sintering temperatures
of (1500/1300), (1500/1200), (1500/1100) and (1450/1300) were similar i.e., increase with
ageing time and reached a reached saturation level. However, sample sintered with sintering
temperature 1400/1200 C exhibited excellent resistant against ageing and hence this profile
would be suitable for sintering of 3Y-TZP samples for biomedical applications.
