Thermoplastic Ceramic Injection Molding of Zirconia Toughened Alumina Components

Abstract

Alumina-toughened zirconia (ATZ) materials are suitable materials for a variety of biomedical applications owing to their high strength, toughness and hydrothermal stability. The prospect of being able to offer ceramic implants to a broader group of patients requires a more cost-efficient near-net-shape manufacturing approach. Small and complexshaped components can be efficiently mass-produced by means of ceramic injection moulding (CIM) with high surface quality and low dimensional tolerances. Compared to the state-of-the-art cold and hot isostatic pressing cycles commonly used for implant production, CIM technology does suffer from lower microstructural quality. During the thermally and rheologically transient mould-filling process, inevitably a certain number of defects are induced by flow textures, weld lines and micro-segregation. A higher level of toughness is therefore beneficial to keep strength and damage tolerance on a sufficiently high level. In order to improve thetoughness of ATZ, in-situ platelet reinforcement with strontium hexaaluminate precipitates was introduced. The influence on processing behaviour, strength and toughness of as-manufactured and final-machined platelet-containing and platelet-free 2.5Y-TZP/15 vol% alumina composites was investigated. Platelets improve the mechanical properties. Weibull statistics show that platelet addition leads to drastic improvements in reliability.

Alumina toughened zirconia from yttria coated powders

“…As such reflexes were also found in yttria free ZTA the unknown phase does not necessarily contain yttria. 26 The average transformability of the three materials correlates very well with the measured average toughness. If we subtract a basic toughness of ∼3 MPa √ m from the measured values, the remaining toughness increment supposedly delivered by transformation toughening K TT divided by transformability T is almost constant K TT /T = 10 = 5/0.5 (TZP) = 2.5/0.25…”

“…For the ATZ materials a trend to higher transformability at higher sintering temperature is clearly visible while the TZP shows a transformability minimum at 1425 • C. A closer look at the XRD results of fracture faces shows an interesting detail which was previously reported for alumina doped Y-TZP, Yb-TZP and yttria free ZTA. 15,16,26 At some sintering temperatures (actually in more than half of the tested parameters) there appear two additional reflexes between the monoclinic (1 1 1) and the tetragonal (1 0 1) reflex. These reflexes are very pronounced especially for the case of ATZ40 sintered at 1425-1450 • C (Fig.…”

Issues in Nanocomposite Ceramic Engineering: Focus on Processing and Properties of Alumina-based Composites

“…For nanocomposite mixtures, it is therefore necessary to pre-alloy the starting powders. Feedstocks derived from intensively milled aqueous dispersions show the required homogeneity (48). …”

Advanced Manufacturing of Hard Ceramics

“…The transient mold filling process may cause flow textures (Gadow, Fischer, & Lischka, 2005). Weld lines or abruptly changing cross-sections are critical points with reduced strength (Kern, 2010). Thus, the mold design is a crucial point to obtain CIM components of high quality.…”

“…This cannot be achieved by standard mixers like sigma blade kneaders. Rather it requires machines like twin screw extruders or shear rollers which are capable of introducing high shear forces (Kern, 2010).…”