ICMCTF2003 Session TP: Symposium TS Poster Session

Monday, April 28, 2003 5:00 PM in Room Town & Country
Monday Afternoon

Time Period MoP Sessions | Topic TS Sessions | Time Periods | Topics | ICMCTF2003 Schedule

TP-1 Electrochemical Corrosion Behaviour of Uncoated and DLC Coated Medical Grade Co28Cr6Mo
A. Dorner-Reisel (Freiberg University of Mining and Technology, Germany); C. Schürer (Institute of Physical and Mechanical Technologies Chemnitz, Germany); G. Irmer (Freiberg University of Mining and Technology, Germany)

Thin wear protecting films, like TiN, CrN or diamond-like carbon (DLC), are potential coatings on metallic medical implants [1-3]. However, the results from tribological and corrosion tests are contradictory. Some studies reveal superiority of DLC coatings in comparison with uncoated metallic substrates, while other give no evidence of an improved performance. This outcome stresses the importance of paying attention to the deposition method as well as parameters and the correlating nano- and microstructural features, the kind of substrates and the coatings adherence. These features directly influence the mechanical, electrochemical and tribological behaviour, but also effect the biological interaction at the surface, and with this indirectly the coatings wear and corrosion properties.

In the following study, diamond-like carbon coatings (0.8 micrometer, 2.7 micrometer) were deposited on polished Co28Cr6Mo-samples by a plasma deposition method (direct current discharge) using gaseous hydrocarbon as precursor. The electrochemical behaviour of DLC is investigated in 0.89 wt.% NaCl solution and compared with the behaviour of the uncoated medical grade CoCrMo. For 500 h the potential was measured against time under open circuit conditions. In addition, potentiodynamic polarisations were carried out starting from the rest potential into the anodic direction, and subsequently, into the cathodic direction. The polarization curves are evaluated and correlated to the nano- and microstructure of the coatings (Raman spectroscopy, Scanning electron microscopy). Additional information is given by hardness measurements (load 4 mN) and characterisation of the surface topography by atomic force microscopy (AFM).

[1] Bolton, J., X. Hu, In vitro corrosion testing of PVD coatings applied to a surgical grade Co-Cr-Mo alloy, J. Mater. Sci.: Mater. Med. 13 (2002) 567-574.

[2]Platon, F., P. Fournier, S. Rouxel, Tribological behaviour of DLC coatings compared to different materials used in hip joint prostheses, Wear 250 (2001) 227-236.

[3] Xu, T., L.Pruitt, Diamond-like carbon coatings for orthopaedic applications: an evaluation of tribologcal performance, J. Mater. Sci.: Mater.Med. 10 (1999) 83-90.

TP-4 Ti(Ta)O2 Film Fabricated by Magnetron Sputtering and Plasma Immersion Ion Implantation and Deposition: Comparative Study
J.Y. Chen, Y.X. Leng, G. Wan, P. Yang, H. Sun, N. Huang, J. Wang (Southwest Jiaotong University, PR China)

Scientists are pursuing high-level hemocompatible materials with all possible technology in these years. Specific surface modifications of materials for good blood compatibility are developed by biomaterials researchers. As an effective method, thin film deposition has been applied to modify metallic biomaterials such as stainless steel and Titanium, which have been applied as substrates of stents and mechanical heart valves etc, for improving blood compatibility. In this paper, Titanium oxide films doped with Ta (Ti(Ta)O2 film) were fabricated using magnetron sputtering and plasma immersion ion implantation and deposition (PIII-D) respectively. The microstructure of the Ti(Ta)O2 films was investigated using X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The blood compatibility of the films was evaluated using in vitro platelet adhesion investigation. The surface energy of the film was calculated by Young function according to the contact angle measurement. The interfacial energy between the film surface and stimulant body fluids such as Hank's liquids and Ringer's liquid was further calculated. In addition, the investigation of endothelial cells growth in vitro on the films was also performed. The different characteristics and properties of the Ti(Ta)O2 films synthesized by different deposition methods were described. The blood compatibility mechanism of Ti(Ta)O2 film was also discussed.

Acknowledgement: Financially supported by the State key basic research G1999064705 and 2001AA320604.

TP-5 Biocompatibility of Hydrogen Free Diamond-like Carbon (DLC) Prepared by Nitrogen Plasma Immersion Ion Implantation - Deposition (PIII-D)
S. Kwok, P. Yang, P.K. Chu (City University of Hong Kong)
Amorphous hydrogenated carbon films (a-C:H) has attracted much attention as biomaterials, for instance, in artificial heart valves, bone implants, and so on because of its chemical inertness, low coefficient of friction, high wear resistance and good biocompatibility. Recently, we have begun to investigate the biomedical properties of hydrogen free DLC as an alternative material. Hydrogen free DLC films with nitrogen are synthesized using plasma immersion ion implantation-deposition (PIII-D) using a pulsed vacuum arc plasma source. Different N to Ar (FN / FAr) flow ratio is used in our experiments. The structure and properties of the film are studied using Raman spectroscopy, atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), and X-ray photoelectron spectroscopy (XPS). Platelet adhesion test is conducted to assess the biocompatibility characteristics of the film. The impact on the blood compatibility by the presence of nitrogen is investigated and the results will be presented in this paper.
TP-6 Electrochemical Behaviour and Characterisation of Plasma Nitrided Ti-5Al-2Nb-1Ta Newly Developed Orthopaedic Alloy
S. Gokul Lakshmi (Anna University, India); M.A.K Babi (DBS Plasma Technologies Pvt. Ltd., India); S. Tamilselvi, D. Arivuoli (Anna University, India)
Titanium and its alloys are used as an implantatble material due to its excellent biocompatibility, light weight, low modulus and excellent corrosion resistance. Though it has a good corrosion resistance in static conditions, the passive layers are removed when they are subjected to wear and used in physiological environment. Also much concern has developed over the release of Vanadium ions and the possibility of toxic effects. So Ti-6Al-4V alloy which are used for orthopaedic implants are now replaced by vanadium free Ti-5Al-2Nb-1Ta alloys as both Nb and V are beta stabilizers. In order to improve the corrosion behaviour of these alloys, the surface of the alloys are modified by the formation of Titanium nitride particles, due to its good biocompatibility and high hardness. Plasma nitriding has been employed for producing titanium nitride, because plasma diffusion treatments allow us to control the formation of phases and also it produces thick nitride layers. So Ti-5Al-2Nb-1Ta alloy has been plasma nitrided for different treatment parameters. The surface nitrided alloy has been subjected to a number of characterisation techniques in order to characterise the nitrided surface. Surface microhardness measurements have been carried out to evaluate the effect of processing parameters. The phase analysis of the layers was carried out using XRD. Corrosion experiments are conducted in Hanks balanced salt solution. The corrosion resistance was estimated by analysing the cyclic polarisation curves recorded at a scan rate of 1mV/s. The results will be discussed
TP-7 Global-to-local Thermo-mechanical Finite Element Modeling of Die Casting
S.L. Carrera, G.G.W. Mustoe, J.J. Moore (Colorado School of Mines)

Die casting is a high temperature process that generates extreme cyclic variation of stresses and strains in the H13 steel within a shot cycle. Finite element thermo-mechanical simulation of the die casting process is an important in the development of the engineering design of thin films for specific die casting process applications. For example, this tool can design an optimal coating system with spatial varying compositional architecture tailored for a varying thermal-mechanical environment in different parts of the die cavity.

In this paper a two-step non-linear thermo-mechanical finite element analysis is developed and applied to study these cyclic conditions within a die cast coating system. The first step is a global thermo-mechanical analysis of the complete die. These results determine the critical points on the interior surface of the die. This information is illustrated in stress and strain path plots along the interior of the die surface. Note, critical points are based on the von Mises yield criterion and the deviation of the surface strain from the free thermal expansion strain.

The second step is a local finite element analysis model that analyzes the behavior of a die coating system at the previously identified critical interior die surface locations. The boundary conditions of the local analysis are matched to the detailed surface strain data and the transient temperature results obtained previously from the global analysis. From the results of the local modeling various coating architectures can be studied and optimized.

Time Period MoP Sessions | Topic TS Sessions | Time Periods | Topics | ICMCTF2003 Schedule