| Titanium alloys (Ti6Al4V) are widely used in biomedical aspects because of the relatively low density, high strength, corrosion resistance. But their wear resistance is poor and their biocompatibility should be improved. Dental drills have a number of problems associated with low cutting efficiency and short life. Diamond films have a series of excellent physical and chemical properties, such as high hardness, low friction coefficient, high wear resistance, high thermal conductivity and good biocompatibility, and so on. Therefore, the aim of this study is to overcome the main problems extensively existing in the application of dental drills and titanium alloys by depositing diamond films, for example, to improve the adhesion of the diamond films against the substrates and the substrates' wear behavior.In the present paper, the nucleation and growth of diamond films were studied systematically using a bell-jar type MWPCVD (microwave plasma assisted chemical vapor deposition) setup. The diamond films on Ti6Al4V were deposited through increasing the content of CH4 and introducing Ar plasma separately. The optimized technique on the titanium was: CH4/H2 1.11%-0.86-0.60 or CH4/(H2+Ar)1.09%-0.83%-0.59%, microwave power 700W,gas pressure 4.7KPa. Diamond films with good quality were deposited on the cemented carbide etched by acid to remove cobalt and the cobalt-deficient gradient cemented carbide. The optimized technique on the cemented carbide was: CH4/H20.60%-0.43-0.26, microwave power 1000W, gas pressure 4.7 KPa.In comparison with the deposition on the etched cemented carbide, by studying the diffusion of cobalt quantitatively, it was proved that the adhesion of the diamond films to the cobalt-deficient gradient cemented carbide was improved up to 30% without the loss of strength of the substrate. It provides a promising future to improve the cutting efficiency and the life of dental tools.The diamond films on titanium alloys were deduced from Raman spectroscopy and the results indicated that they were typical nano-diamond films. The surface morphology and diamond grain size of these coatings were investigated by scanning electronic microscopy (SEM) and atomic force microscopy (AFM). The results exhibited a fine morphology with an average grain size about 40nm and a smooth surface. AFM showed that the surface roughness was 19nm (2μm*2μm). Diamond film deposited from CH4-Ar-H2 was more uniform. The roughness was about 14.2 nm (2μm*2μm). The scratch and Vickers indenting tests showed that there were good attachment between the films and the substrate. The critical load of scratch tests were about 29N. The max of them was over 70N. Under the indenting load 490N,a few cracks appeared in the diamond film at the corner of indenter. The nano-hardness of diamond films was relatively low (13-15GPa).The tribological tests indicated that nanocrystalline diamond films could improve tribological properties of Ti6Al4V efficiently. The experiment was carried out with the following conditions: SiC ball, in open air; load: 2N;velocity: 10cm/s; relative humidity: 30%; temperature: 26℃. The coefficient of titanium alloy substrates was about 0.52, with a great deal of abrasive debris and deep furrow. For the nanocrystalline diamond films, the coefficient was decreased to about 0.25, with no crack and desquamation. In comparison with titanium substrate, there was an obviously improvement in surface energy, kinetic clotting time and hemolysis with nanostylline diamond films. The data of these experiments were just as DLC films' and very close to LTIC films'.
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