Surface yttria content and hydrothermal ageing behaviour of two step sintered 3Y-TZP ceramics

In this work the effect of surface yttria concentration on hydrothermal ageing of two-step sintered (TSS) 3 mol. % yttria stabilised tetragonal zirconia polycrystalline (3Y-TZP) ceramics was investigated. Green compacts were prepared by bench pressing and sintered using a two-step sintering with first step sintering temperature of 1400°C for one minute and second step sintering temperature of 1200°C at different holding times of 2, 10 and 20 hours. Surface morphology and surface yttria content of the sintered samples were investigated by using Xray florescence spectroscopy (XRF) and field emission scanning electron microscopy (FESEM), respectively. It was found that the TSS effectively suppressed the grain growth. Increasing the holding time increased densification. Also, an increment in the surface yttria content with increasing holding time was observed. The ageing studies were conducted in an autoclave containing super-heated steam at 180°C and 10 bar pressure for 100 hours. Ageing resistance increased with increasing second step sintering time. The enhanced hydrothermal degradation of lower holding time samples can be attributed to the deficiency of surface yttria. Effect of ageing on surface yttria concentration and surface morphology were also investigated by using XRF and FESEM, respectively. The surface yttria concentration decreased with ageing which confirms leach out of surface yttria during hydrothermal ageing.