Mechanical and Phase Stability of Zirconia Toughened Alumina

Abstract

The JMM-ZTA, a kind of zirconia-toughened alumina, is a bearing ceramic newly developed for artificial joints. Although it has already been reported that mechanical strength and fracture toughness are higher in the JMM-ZTA than in alumina, the stability of the JMM-ZTA has not been studied in detail yet. In the present study, the stability of the JMM-ZTA with respect to mechanical strength and crystalline phases was examined under hydrothermal environment, and the results were compared with those of alumina. Both the 4-point bending strength and the fraction of monoclinic zirconia unchanged even after the aging test at 121°C for 300 h. These results indicate that the JMM-ZTA possesses quite excellent stability to be used as bearing material of artificial joints.

Ceramics and ceramic coatings in orthopaedics

“…ZTA strengths as high as 1248 MPa have been observed, and flexural strengths of up to 1400 MPa have been reported for AMC on a series of ∼40 production lots (cf., Table 1a) [154,243]. In vivo fracture rates for AMC are extremely low, at 0.001% [40].…”

“…They were introduced in an attempt to overcome the hydrothermal deficiencies of Y-TZP and the relatively modest strength of Al 2 O 3 . At one end of the composition spectrum are zirconia-toughened alumina (ZTA) [153,154] and an alumina matrix composite (AMC) [152]. ZTA is a fully dense ceramic consisting typically of about 7-25 wt.% unstabilized ZrO 2 or Y-TZP incorporated into an Al 2 O 3 matrix [155,156].…”

“…All have been tested and determined to be biocompatible [163,164]. They have excellent strength, toughness, and hardness [154,165,166], and are highly abrasion [167] and wear resistant [168][169][170][171][172][173][174]. Clinical studies using these devices have been on-going since their introduction with acceptable overall outcomes [172,[175][176][177][178].…”

“…However, this ceramic is also highly susceptible to hydrothermally induced phase transformation because of the large proportion of t-ZrO 2 grains, although its kinetics are reportedly retarded when compared to Y-TZP ceramics [162]. Representative microstructures of Y-TZP [213] and ZTA [154] are shown in Fig. 1(b) and (c), respectively.…”

“…While the current standard in bioinert ceramics is BIOLOX ® delta (CeramTec, Plochingen, Germany), its position may eventually be challenged by other ZrO 2 and ZTA compositions having both high strength and little or no LTD, or by non-oxide ceramics such as Si 3 N 4 with elevated strength and no LTD. As an example of an improved ZrO 2 , Matsui et al demonstrated that addition of a small amount of germanium oxide (0.30 mol%) to a 3 mol% Y 2 O 3 -doped ZrO 2 coupled with low-temperature sintering produced a fully dense nano-crystalline Y-TZP (grains <300 nm) which exhibited no LTD for 4 years in a steam autoclave at 140 • C [572]. As other examples, ZTA nano-composites which exclude the use of yttria, or which incorporate zirconia nano-particles (<500 nm) evenly dispersed within alumina grains have been developed [154,573]. Both composites result in high strength, tough, and highly LTD resistant ceramics.…”