Low-temperature ageing of zirconia-toughened alumina ceramics and its implication in biomedical implants

Abstract

Changes in crystalline phases resulting from low-temperature ageing of different yttria doped and non-doped zirconia-toughened alumina composites and nanocomposites were investigated under controlled humidity and temperature conditions in autoclave. A classical powder mixing processing route and a new modified colloidal processing route were used to process the composites. Different compositions ranging from 2.5 wt.% zirconia in a matrix of alumina to pure zirconia (3Y-TZP) were studied. It was observed that Al2O3+yttria stabilised ZrO2 composites exhibited significant ageing. However, ageing was much slower than traditionally observed for Y-TZP ceramics, due to the presence of the alumina matrix. Ageing was clearly limited for zirconia content beyond 25 wt.%. On the other side of the spectrum, Al2O3+2.5 wt.% ZrO2 initially presented a monoclinic fraction but did not show any ageing degradation. These composites seem to represent the best choice between slow crack growth and ageing resistance.

Selective etching of injection molded zirconia-toughened alumina: Towards osseointegrated and antibacterial ceramic implants

“…Even if ZTA is much more resistant to LTD than monolithic zirconia, it has been shown that it can still present a certain degree of surface tetragonal to monoclinic phase transformation in the presence of water [39][40][41]. All these elements lead to the following conclusion: to ensure longterm reliability and patient safety, any change in the processing of zirconia-containing ceramics should be accompanied with a careful assessment of its impact on mechanical properties and ageing sensitivity, especially in the presence of porosity.…”

Evaluation of hardness and fracture toughness, coupled with microstructural analysis, of zirconia ceramics stored in environments with different pH values

“…Alloying pure zirconia with stabilizing oxides such as CaO, MgO, Y 2O3, or CeO2 allows the retention of the tetragonal structure at room temperature. Elimination of the stress-induced t→m transformation efficiently prevents crack propagation and enhances fracture toughness 1,[3][4][5][6][7] . Partially stabilized zirconia (PSZ) has been extensively studied for decades and is now widely used in numerous industrial and biomedical applications.…”

Relationship between residual stresses and mechanical behavior in ceramic composites

“…This shows that almost all the monoclinic phase in the zirconia starting powder was transformed to tetragonal structure during heating at high temperature (at around 1170 ℃) [64]. No transformation from tetragonal zirconia to monoclinic zirconia (t→m transformation) occurred during the cooling process from the high sintering temperature to room temperature, in agreement with the data published [222,223]. This could be explained by the stabilizing action of Y 2 O 3 on zirconia, as well as the restraint from phase-change volume expansion by Al 2 O 3 matrix during cooling.…”