C. C. Klepper, J. M. Williams, R. C. Hazelton, M. D. Keitz, HY-Tech Research Corporation, Radford, VA; J. J. Truhan, L. Riester, P. J. Blau, Oak Ridge National Laboratory, Oak Ridge, TN; J. P. Anderson, O. O. Popoola, Zimmer, Inc., Warsaw, IN
Efficient deposition of pure boron and other boron-rich coatings by use of the cathodic arc plasma generation technique have been developed over a period of several years, and several applications are emerging2. One of these applications, and the focus of this paper, is surface modification of cast CoCrMo components, used for knee joint-replacement. The idea driving the research effort is that boron-rich coatings can lead to reductions in the wear of UHMWPE counter-surfaces significantly beyond what is possible with mechanical polishing. The latter is limited, in the case of cast components, by the substantially higher hardness of carbide-rich and molybdenum-rich regions of the cast components over the base alloy. During mechanical polishing, the harder regions tend to form protrusions, which in turn can contribute to wear of the UHMWPE. The high reactivity of boron with all the components of the alloy, coupled with the self-lubricious nature of boron oxide in a humid environment, make boron an excellent candidate for a surface coating material to mitigate this wear mechanism. In this paper, results are presented from initial wear studies of coated components, using UHMWPE pins in reciprocating motion (86,400x13.4mm) in saline solution and under loads of ~10 MPa. Analysis was by profilometry and Rutherford backscattering spectrometry (RBS). For the uncoated material there was a transfer film of UHMWPE in the wear track of about 150 nm in thickness. For the boron-coated sample, there was no detectable transfer film. Moreover, there was no thinning of the boron coating. The friction coefficient for the uncoated material was about 0.02, and the value for the coated was about 0.01. In separate experiments, the boron and boron-coated alloy have been shown to be quite biocompatible.2________________________________________________________________________
1Research supported by NIH/NIAMS, Grant Number 1 R43 AR051262-01.
2J.M. Williams et al., ISEC’05 Proceedings, in print.
Summary: Results are presented from initial wear studies of cast Co-Cr-Mo components, some treated with a boron-rich, coating process. The pin-on-disk studies, using UHMWPE pins and reciprocating motion in saline solution, support a reduction in the wear of the pins due to the coating. The friction coefficient is also reduced.
