Raman Spectroscopic Analysis of Advanced Ceramic Composite for Hip Prosthesis

Abstract

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.