Journal of The Australian Ceramic Society Volume 51[1], 2015, 16 – 21 16 © Copyright 2015, The Australian Ceramic Society ISSN 0004-881X The Effect of Aluminum Oxide (Al 2 O 3 ) and Cerium Oxide (CeO 2 ) on the Structural and Mechanical Properties of Yttria Tetragonal Zirconia Polycrystal (Y-TZP) M. Golieskardi * , M. Satgunam, D. Ragurajan , M.N.M. Ansari Centre for Advance Materials, University Tenaga Nasional, Kajang, 43000 Selangor, Malaysia Email: mohsen_golieskardi@yahoo.com Available Online at: www.austceram.com/ACS-Journal ABSTRACT The effect of additions of Al 2 O 3 and CeO 2 (up to 1 wt %) on the sintering behavior of yttria-stabilized Tetragonal Zirconia Polycrystals (Y-TZP) were studied. The effects of Al 2 O 3 and CeO 2 on the Vickers hardness, bulk density, fracture toughness and Young’s modulus were carried out on the sintered samples. The sintering temperature was ranging from 1250 °C to 1450 °C with the ramp rate of 10°C/min. The results revealed that the doped samples demonstrated a stronger effect in contrast with the undoped samples. The relative densities were above 97.5 % of theoretical (i.e. > 6.1 gcm -3 ) could be obtained in Y-TZPs sintered at low temperatures, 1350 °C. The hardness’s value of Y-TZP was increased in the 1 wt % Al 2 O 3 and CeO 2 -doped samples when sintered above 1400 °C. Keywords: Aluminum Oxide; Cerium Oxide; sintering behavior; Y-TZP; Mechanical Properties INTRODUCTION Yttria stabilized tetragonal zirconia polycrystals or subsequently known as Y-TZP, is engineered to take full advantage of transformation toughening effect [1, 2]. This ceramic, when fired, consists of a single phase tetragonal structure of fine grains (< 0.5 μm) which makes it ideal for many structural applications. They possess very high modulus, high compressive strength, unique combination of mechanical properties: high wear resistance, low coefficient of friction, very good biocompatibility and the good compromise between fracture resistance, crack resistance and wear behaviour makes this material one of the best candidates for many components including orthopaedic prostheses as a replacement for metallic materials [3- 5]. This is mostly the result of transformation toughening mechanism discovery (a mechanism through which the stress induced tetragonal is transformed to monoclinic phase in the vicinity of a propagating crack front, resulting in crack suppression and volume expansion) [6] creating toughness and strength that is far greater than that of the majority of ceramics and nearer to the strength of low strength metals [7-9]. However, in spite of the many favorable characteristics such as high strength, high toughness and good wear properties, TZP ceramics display an unfavorable low temperature ageing phenomenon especially in humid atmosphere (water and steam) at temperatures ranging from 60°C to 500°C, a phenomenon widely known as low temperature degradation (LTD) or hydrothermal ageing [10-12]. The degradation which occurs is normally accompanied by mechanical property deterioration attributed to the ageing-induced tetragonal (t) to monoclinic (m) phase transformation, although there is still a lack of understanding of the mechanism responsible for monoclinic nucleation [13-16]. Kobayashi et al. [17] who first discovered a serious limitation of Y-TZP ceramics for applications near 250°C in moist environment. The authors revealed that the ceramic can suffer a slow, tetragonal to monoclinic phase transformation at the samples surface in a humid atmosphere, followed by microcracking and a serious loss in strength. Ever since then, many researchers have experimented with Y-TZP with an attempt to understand the basic micro mechanisms of the ageing-induced (t) to (m) phase transformation and to suppress this LTD phenomenon [18-21]. A typical method that has been used in order to suppress ageing is by using appropriate sintering