Effect of Sintering Holding Time on Tetragonal Phase Stability of Yttria Stabilized Zirconia Ceramics

Abstract

In this study, the effect of second step sintering holding time on LTD of 3 mol% yttria tetragonal zirconia polycrystals (3Y-TZP) ceramic was studied. The Zirconia powder was die pressed followed by cold isostatically pressed (CIP) at 200 MPa, and the samples were initially heated to a first step temperature of 1400°C with constant heating rate 10°C/min and the samples were stand still for 1 minute. Then cooled down to the second step temperature of 1200°C and maintained at that temperature for 2 and 10 hours before cooled down to the room temperature. The other sample was sintered by using Single Step Sintering (SSS) at 1400°C for two hours. The phase content in the zirconia samples was measured by using X-ray diffractometer. Average grain size was calculated by using Field Emission Scanning Electron Microscope (FESEM). The low temperature degradation study was conducted in an autoclave containing superheated steam at 180°C and 10 bar pressures for periods up to 60 hours. Results revealed that the two-step sintering (TSS) effectively controlled the grain growth than SSS and subsequently ageing. Increase in second step sintering holding time from two to ten hours also increased the densification and hydrothermal ageing resistance of Y-TZP ceramics.

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

“…The dominant mechanism for frozen grain growth is suppression of grain boundary migration before the second stage of sintering caused by immobilizing the triple-point junctions, due to rapid cooling after first step sintering and densification achieved by grain boundary diffusion (Sutharsini et al, 2018). Then it was found that TSS enhanced the hydrothermal ageing resistance which is consistent with previous work (Sutharsini et al, 2017(Sutharsini et al, , 2018Vignarajah et al, 2019). The interesting observation here is that two step sintering revealed different ageing behaviours for different samples with the same grain size distribution.…”

“…The interesting observation here is that two step sintering revealed different ageing behaviours for different samples with the same grain size distribution. In addition, regardless of the same grain size, the tetragonal to monoclinic phase transformation decreased with increasing sintering holding time (Sutharsini et al, 2017(Sutharsini et al, , 2018Vignarajah et al, 2019). To identify the mechanism behind the unique ageing behaviour, the surface yttria concentration of the samples was studied.…”

“…Grain size of the 3Y-TZP was controlled by tailoring the sintering condition (Mazaheri et al, 2008;Sutharsini et al, 2018Sutharsini et al, , 2017Sutharsini et al, , 2014bVignarajah et al, 2019). Grain size increased with increasing sintering temperature (Ramesh & Gill, 2001;Ramesh et al, 2013Ramesh et al, , 2016Ramesh et al, , 2018Sutharsini et al, 2014a;b, 2017Ting et al, 2016;Ubenthiran et al, 2018;Dhuban et al, 2019;Ng et al, 2019;Vignarajah et al, 2019). However, high temperature sintering is important for densification which directly influences the mechanical properties.…”

“…However, high temperature sintering is important for densification which directly influences the mechanical properties. Two step sintering is a promising approach to achieve high densities with controlled grain growth (Mazaheri et al, 2008;Sutharsini et al, 2014bSutharsini et al, , 2017Sutharsini et al, , 2018Vignarajah et al, 2019). In the two-step sintering technique, the samples are sintered at higher temperature for a short time to achieve critical grain size and then it is sintered at lower temperature for a long time to reach maximum densification.…”