The purpose of this study was to characterize metallurgical and tribologica
l events occurring at the articulating surfaces of metal-metal implants tes
ted in a hip simulator in order to gain understanding of the wear character
istics of Co-Cr-Mo alloys. The surfaces of 12 implant heads, made of either
cast, low carbon wrought, or high carbon wrought Co-Cr-Mo material, were e
xamined using scanning electron and atomic force microscopes. Three of the
implants were examined prior to simulator testing, three after three millio
n cycles of testing, and six after six million cycles of testing. Initially
the carbides in the cast and high carbon wrought components were proud of
the surface. With testing, in the high carbon wrought components, the carbi
des were worn below the matrix surface and were also a source for micropits
. In the cast components, some of the carbides remained proud of the surfac
e, while others were worn below the matrix surface with increased test cycl
es. Some of the carbides in the cast alloy experienced partial or full pull
-out, resulting in micropits. All three alloys showed evidence of matrix we
ar through a process resembling delamination in which layers of material ap
peared to be removed. (C) 1999 Elsevier Science S.A. All rights reserved.