Biomedical Engineering Reference
In-Depth Information
10.6.1 Introduction
339
10.6.2 E - Field Calculations for Electrode Design
340
10.6.3 Shaping of Homogeneous and FGM Acetabular Cup Inserts
340
10.7 Sintering and Microstructural Evaluation
344
10.7.1 Introduction
344
10.7.2 Sintering Kinetics of Al 2 O 3 , ZrO 2 and Their Composites
345
10.7.3 Optimization of Grain Size of Al 2 O 3 Composites
346
10.7.4 Observation of Processing Defects in FGM Materials
348
10.8 Conclusions
351
10.9 Future Perspectives
352
Acknowledgments
353
References
353
10.1 OVERVIEW
Many materials are used in medicine for a variety of applications ranging from
total replacement of hard tissues (such as bone plates, pins, joint, dental implants,
and so on), repair, diagnostic or corrective devices (such as pacemakers, heart
valves, and so on). Not only the mechanical properties are important, but also the
material should be biocompatible with the human body and stable for a long
period. Due to their excellent properties such as high strength, biocompatibility,
and stability in physiological environments, ceramics are investigated as bone
substitute materials. In this way, ceramic components have been used for total hip
joint replacement components in Europe since the early 1970s. Alumina and zir-
conia monoliths are mainly used for these components. However, zirconia can
undergo low temperature degradation in aqueous environment.
Current research is focusing on increasing the strength and wear resistance,
meanwhile reducing the size and extending the lifetime of ceramic components.
This chapter will briefl y review the present state-of-the-art with respect to ceramic
material development for total hip joint replacement (THR). In addition to
ceramic monoliths, ceramic composites such as zirconia-toughened alumina and
other alumina matrix composites are currently investigated. Another possibility
to increase the strength is to use components based on alumina and zirconia with
a functionally-graded composition. The latter possibility has been the focus of the
authors' research and will be described in some detail. The composition gradient
can be established during shaping by means of electrophoretic deposition (EPD)
to obtain a pure alumina surface region and a homogeneous alumina/zirconia
composite core with intermediate continuously graded regions to generate
thermal residual stresses after sintering. The gradient profi les are designed to
obtain maximum compressive surface stresses and minimum tensile stresses in
the core of the component to increase the strength and wear resistance compared
to pure alumina components. Practical aspects of this new production technology
will be described, including the method to control the composition gradient,
the electric fi eld calculations necessary to design the electrodes, drying, and the
sintering conditions.
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