A ceramic hip‐joint femoral head, made of a zirconia‐toughened alumina‐matrix material with the addition of small amounts of mixed oxides, has been evaluated with respect to environmental surface degradation in a moist environment. Microscopic insight into environmental surface degradation could be obtained according to Raman and fluorescence microprobe spectroscopies. By adopting an optimized confocal configuration for the optical probe, spectroscopic assessments could be performed in very shallow volumes, thus minimizing the effect on the spectra of sub‐surface portions of the material. Two main phenomena have been envisaged: (i) transformation of zirconia dispersoids from tetragonal to monoclinic polymorph, induced by aging periods at 121°C (0.1 MPa) in a vapor environment (in addition to a fraction of a monoclinic polymorph ≅20 vol% present in the as‐received femoral head); (ii) evolution of the (equilibrium) residual stress field stored within the joint surface from a tensile field in the as‐received material to a slightly compressive stress field after several hours of aging in a moist atmosphere. Exposures in vapor >50 h brought the joint surface into an increasingly tensile stress state. This residual stress field on the material surface may hinder the long‐term wear resistance of the load‐bearing femoral head, especially in the presence of microscopic impingements by microseparation contact and third‐body wear.

A Raman microprobe spectroscopy characterization of microscopic fracture mechanisms is presented for a natural hydroxyapatite material (cortical bovine femur) and two synthetic hydroxyapatite-based materials with biomimetic structures-a hydroxyapatite skeleton interpenetrated with a metallic (silver) or a polymeric (nylon-6) phase. In both the natural and synthetic materials, a conspicuous amount of toughening arose from a microscopic crack-bridging mechanism operated by elasto-plastic stretching of unbroken second-phase ligaments along the crack wake. This mechanism led to a rising R-curve behavior. An additional micromechanism, responsible for stress relaxation at the crack tip, was recognized in the natural bone material and was partly mimicked in the hydroxyapatite/silver composite. This crack-tip mechanism conspicuously enhanced the cortical bone material resistance to fracture initiation. A piezo-spectroscopic technique, based on a microprobe measurement of 980 cm(-1) Raman line of hydroxyapatite, enabled us to quantitatively assess in situ the microscopic stress fields developed during fracture both at the crack tip and along the crack wake. Using the Raman piezo-spectroscopy technique, toughening mechanisms were assessed quantitatively and rationally related to the macroscopic fracture characteristics of hydroxyapatite-based materials.

Three kinds of processing procedure, including conventional sintering, hot-isostatic pressing, and their combination, were explored to prepare hydroxyapatite-silver composites with high density and improved ceramic-metal interface properties. Optimizing the densification procedure, which allowed the desired fraction of Ag to remain within the apatite matrix after densification, has solved a problem related to the low wettability of Ag on hydroxyapatite. The major outcome of this study is that hot-isostatic pressing enables to reinforce the interface between hydroxyapatite and silver, thus improving the structural consistency of the prepared composite. Results are supported by investigations on microscopic fracture mechanisms. It is shown, that a toughening effect arose from the microscopic crack-bridging mechanism operated by the elasto-plastic stretching of unbroken Ag ligaments along the crack wake. A Raman piezo-spectroscopic technique enabled the in situ quantitative assessment of this bridging toughening mechanism.

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Surface deterioration of a retrieved zirconia ceramic femoral head after total hip arthroplasty has been studied on a microscopic level by means of Raman spectroscopic techniques. Two kinds of microscopic quantitative information could be achieved: (i) tetragonal-to-monoclinic phase transformation maps were collected with a micrometer spatial resolution on selected areas of the femoral head; and, (ii) the associated residual stresses stored within the tetragonal phase were also mapped. A clear correlation was found between the degree of phase transformation and the residual stress magnitude, which was in turn related to impingement of the titanium metal backing of the cup on the ball.