Effect of N-Implantation on the Corrosive-Wear Properties of Surgical Ti-6Al-4V Alloy
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EFFECT OF N-IMPLANTATION ON THE CORROSIVE-WEAR PROPERTIES OF SURGICAL Ti-6A1-4V ALLOYt
J. M. WILLIAMS,*
G.M. BEARDSLEY.* R. A. BUCHANAN.** AND R. K. BACON**
*Solid State Division, Oak Ridge National Laboratory, P. 0. Box X, Oak Ridge, Tennessee 37830; **The University of Alabama, Birmingham, Alabama 35294
ABSTRACT The effects of N-ion implantation on the corrosive-wear properties of Ti-6Al-4V, an alloy used for construction of the femoral component of artificial hip joints in humans, were tested. In corrosive-wear tests designed to simulate pertinent hip-joint parameters, electrochemical corrosion currents were measured for cylindrical samples in saline electrolyte in an arrangement which allowed the samples to be rotated between loaded polyethylene pads simultaneously with the current measurement. To further quantify material removal, Zr markers were ion-implanted into some samples so that, by use of Rutherford backscattering, material removal could be detected by changes in position of the marker relative to the surface. Corrosion currents were greatly reduced by implantation of approximately 20 at. % N, but even implantation of the Zr markers also reduced corrosion currents. The marker experiments confirmed the low rate of material removal for the implanted samples.
INTRODUCTION The femoral component of most modern, surgically implanted, total hipjoint systems consists of an integral stem and ball, constructed of a suitable alloy. As the joint moves the ball works in an acetabular cup constructed of ultra-high molecular-weight polyethylene (UHMWPE). The alloy, Ti-6AI-4V, is receiving increased use for the femoral component because of its excellent tensile strength, fatigue strength, low density, high corrosion resistance and substantial ductility [1]. Also, the low elastic modulus of the alloy contributes to good adhesion with living bone. Additionally, the alloy is considered to be more biocompatible than the Crcontaining alloys [2,3]. There is nevertheless a continuing interest in reducing the amount of debris and corrosion products introduced into the body from prosthetic components, even those of Ti-6AI-4V, partly because dispersal of sufficient quantities of substances that are well-tolerated in bulk form, e.g. polyethylene, can cause adverse tissue responses [2]. General concerns are with effects such as inflammatory responses [2], increased susceptibility to infection [4], and sensitizing reactions which can cause loosening of prosthetic components and bone loss [5]. On the long term, systemic effects such as effects on blood-filtering organs cannot be ruled out, and at still longer times carcinogenicity might manifest itself [3]. It is suspected that wear of both Ti-alloy components and their UHMWPE wear partners may be much higher than for other alloys working against UHMWPE [1]. It was considered desirable to investigate, and possibly, ameliorate such effects. tResearch sponsored in part by the Division of Materials Sciences, U. S. Department of Energy, under contract W-7405-eng-26 with the Union
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