Mechanical properties and microstructural analysis of a diamond-like carbon coating on an alumina/glass composite
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Mechanical properties and microstructural analysis of a diamond-like carbon coating on an alumina/glass composite S. Christiansen, M. Albrecht, and H. P. Strunk Universit¨at Erlangen-N¨urnberg, Institut f¨ur Werkstoffwissenschaften-Mikrocharakterisierung, Cauerstr. 6, 91058 Erlangen, Germany
H. Hornberger and P. M. Marquis University of Birmingham, School of Dentistry, Biomaterials Unit, St. Chad’s Queensway, Birmingham B4 6NN, United Kingdom
J. Franks Diavac ACM Ltd., 2 Brookfield Ave., Ealing, London W5 1LA, United Kingdom (Received 6 October 1995; accepted 3 April 1996)
We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating.
I. INTRODUCTION
There are essentially three requirements for body implants: (i) a mechanical one: high fracture and fatigue strength and high erosion and wear resistance; (ii) a chemical one: corrosion resistance against fluid environments; and (iii) a biocompatible one.1–4 The alumina/aluminosilicate glass composite In-Ceram (trade name), Fa. Vita, Bad S¨ackingen, Germany5,6 fulfills the mechanical requirements for implants, since it shows outstanding material properties: (i) high strength due to the potential to partly relax strain plastically6 (600 MPa, ball-on-ring test6 ); (ii) the advantage to be easily shaped in a porous prefired stat
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