INTRODUCTION

Ceramics are excellently suited for applications in arthroplasty, mainly total hip, knee and shoulder replacement. As the most prominent representative of this demanding type of material, BIOLOX^®delta is widely used and very successful in the market for more than 10 years. The ability of zirconia phase transformation (t-ZrO₂→m-ZrO₂) in zirconia-platelet toughened alumina (ZPTA) ceramics is an indispensable prerequisite for their excellent mechanical properties. The degree of stabilization of the zirconia tetragonal phase at body temperature is essential for the desired toughening mechanism. Y₂O₃ is the most widely used t-ZrO₂ chemical stabilizer; also microstructure and grain size contribute to t-ZrO₂ phase stabilization. Stabilization must be achieved such that no material degradation will occur in body environment, i.e. in aqueous liquid (synovia), which is known to potentially trigger phase transformation at the surface of ceramic components. In this study, it is shown how phase stabilization in BIOLOX^®delta as a reference material is excellently balanced by means of optimal mechanical performance and environmental stability.