Microstructural Investigation of the Oxide Scale on Zr-2.5NB and its Interface with the Alloy Substrate

Abstract

Oxidized Zr-2.5Nb is being developed as an articular bearing surface for the femoral component in total joint arthroplasty. It has so far demonstrated superior wear performance against ultrahigh molecular weight polyethylene (UHMWPE) with respect to traditional articulating materials such as Co-Cr-Mo alloys. In this investigation, we used thermogravimetric analysis, transmission electron microscopy, and in situ x-ray diffraction techniques to study the microstructure and stress state of the oxide scale grown on Zr-2.5Nb.The oxidation temperature not only determines the kinetics of oxidation but the morphology of the various oxidation products. We have identified the oxidation products of both phases of the two phase alloy and correlated them with the original alloy microstructure. These include not only monoclinic zirconia but also small amounts of tetragonal zirconia and a mixed oxide phase combining both zirconium and niobium. The alloy microstructure both influences the final oxidation products and is reflected in the microstructure of the oxide. The oxide scale itself has a predominantly columnar microstructure which extends from the oxide/metal interface to the outer surface of the oxide. In situ x-ray diffraction measurements revealed that the oxide scale is stressed in compression following cooling and exhibits strong crystallographic texture. The oxide/metal interface is continuous, without pores or voids which might be detrimental to oxide adhesion. In addition, we have identified a phase which develops at the interface between the beta-zirconium grains and the oxide. We have also identified amorphous regions within the oxide scale which serve as sinks for silicon and other impurity elements found in the alloy.

Oxidized Zirconium Head on Crosslinked Polyethylene Liner in Total Hip Arthroplasty: A 7- to 12-year In Vivo Comparative Wear Study

“…It has been suggested that the reduction in wear debris will limit osteolysis and increase the longevity of the implants [4,14,26]. In addition, oxidized zirconium femoral heads have been developed; the design rationale of this surface was the combination of ceramic wear characteristics and the mechanical properties of the metallic substrate [1,5,16,17]. In clinical terms, XLPE has been combined with cobalt-chrome, ceramic, and oxidized zirconium femoral heads [12,29,[33][34][35].…”

“…In most of these studies a cobalt-chrome metallic femoral head was used. Oxidized zirconium femoral heads on XLPE are associated with considerably less wear on hip wear simulators compared with cobaltchrome femoral heads articulating to either CPE or XLPE liners even when damaged [5,17]. Long-term clinical data related to oxidized zirconium on XLPE coupling are lacking with only a few studies showing satisfactory performance in early and midterm stages [13,15,29].…”

“…In January 2003 a prospective randomized study was initiated in our department to evaluate the clinical and in vivo wear performance of an oxidized zirconium head on XLPE (Oxinium; Smith & Nephew, Memphis, TN, USA) [5,13,15] in THA compared with other conventional and hardon-hard bearing surfaces. Written informed consent was obtained from all patients for participation in this prospective study.…”

“…Metal-on-metal combinations have been associated with pseudotumor formation [2,21] and increased metal ion release, which may lead to cell apoptosis and to DNA changes [22]. Oxidized zirconium head technology has been proposed as an alternative bearing surface based on the theoretical assumption that the wear characteristics of a ceramic surface and the metallic substrate can be combined in one head [1,5,16,17]. The combination of oxidized zirconium on XLPE has been tested in vitro and shown satisfactory wear characteristics.…”

Oxidation Microstructures and Interfaces in the Oxidized Zirconium Knee

“…The present contribution, building on prior preliminary reports, [21][22][23] summarizes the results of a series of investigations, undertaken to characterize the chemistry and microstructure of the oxide scale formed on a Zr-2.5 wt% Nb alloy by high-temperature oxidation in air, in order to account for the integrity of the scale/alloy interface responsible for the good scale adherence and surface durability reported in prosthetic application. These investigations have employed thermogravimetry (TGA), analytical transmission electron microscopy (TEM), environmental scanning electron microscopy (ESEM), and hot-stage X-ray diffractometry (XRD) techniques that, in concert, have provided microstructural explanations for the observed efficacy of the oxidation layer in clinical service.…”