Abstract
Titanium nitride (TiN) was deposited on the surface of a cobalt–chromium (Co–Cr) alloy by a hot-wall type chemical vapor deposition (CVD) reactor at 850 °C, and the coating characteristics were compared with those of a physical vapor deposition (PVD) TiN coating deposited on the same alloy at 450 °C. Neither coating showed any reactions at the interface. The face-centered cubic (fcc) structure of the alloy was changed into a hexagonal close-packed (hcp) phase, and recrystallization occurred over at 10 μm of depth from the surface after CVD coating. Characteristic precipitates were also generated incrementally depending on the depth, unlike the precipitates in the matrix of the as-cast alloy. On the other hand, the microstructure and phase of the PVD-coated alloy did not change. Depth-dependent nano-hardness measurements showed a greater increase in hardness in the recrystallization zone of the CVD-coated alloy than in the bulk center of the alloy. The CVD coating showed superior adhesion to the PVD coating in the progressive scratch test. The as-cast, PVD-coated, and CVD-coated alloys all showed negative cytotoxicity. Within the limitations of this study, CVD TiN coating to biomedical Co–Cr alloy may be considered a promising alternative to PVD technique.
Highlights
Cobalt–chromium (Co–Cr) alloys have been widely used as commercial orthopedic implant materials due to their excellent biochemical properties, moderate strength, and their resistance to corrosion and abrasion
Typical γ- and ε-phase diffraction patterns were detected in the Co–Cr alloy substrate (Figure 2a)
All of the diffraction peaks were indexed by the diffraction peaks of the γ-phase (ICSD: PAN 98-007-2476) and the ε-phase (ICSD: PAN 98-008-7135), taking into account the peak displacements and the indexing data of previous X-raydiffractometry diffractometry (XRD) studies [17,20,21]
Summary
Cobalt–chromium (Co–Cr) alloys have been widely used as commercial orthopedic implant materials due to their excellent biochemical properties, moderate strength, and their resistance to corrosion and abrasion Among these properties, the biochemical stability of the alloys is known to be due to the passive film on their surface [1,2]. Due to long-term fatigue friction and the subsequent wear of orthopedic implants, this passive film may become unstable and, as a result, allow metal ions released from the alloys into the body fluids (serum, urine, etc.) to accumulate between the implant and the tissues, causing an inflammatory reaction in the surrounding tissue [3,4]. The strong stress inevitably generated during the coating procedure may cause peeling and buckling of the coating layer at the sharp edges of the implant [13]
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