Surface Modification Of UHMWPE With A-C Based Film And Its Frictional Properties

In recent decades, the amorphous carbon (a-C) films have been studied extensively because of their excellent mechanical properties and outstanding wear resistance, and have been widely used in the fields of machinery, aerospace industry, biomedicine and so on. But the high internal stress of the intrinsic a-C films limits the increase of the film thickness and damages the adhesion between the film and the substrate. In view of this issue, our paper intends to reduce the internal stress of the amorphous carbon films by the fabrication of a transition layer between the matrix and the amorphous carbon film, and by the doping of transition metal elements as well. Besides, the variation law and the internal mechanism between the microstructure and the macro mechanical properties of the a-C film were also studied.Ultra high molecular weight polyethylene (UHMWPE) is composed of non-polar molecules, the low surface energy and molecular inertness of UHMWPE limits the enhancement of the adhesion between the amorphous carbon film and the substrate, and thus restrains its application in many fields. In our paper, the ultra high molecular weight polyethylene was surface-modified by plasma treatment, the plasma modification process changed the surface status of the UHMWPE and resulted in the alteration of the surface morphologies, contact angle, surface hardness, friction coefficient, etc. which were studied in our paper.A 900 nm a-C film including a transition layer was deposited on the surface of plasma-treated UHMWPE using an unbalanced magnetron sputtering equipment. Compared to the original ultra high molecular weight polyethylene matrix, the hardness was improved from 47 MPa to 720 MPa and the wear rate under the load of 1 N in bovine calf serum solutions decreased from 9.82×10-15 m3 N-1 m-1 to 4.78×10-15 m3 N-1 m-1 after coating, in addition, the contrast test shows that compared with the amorphous film without a transition layer, the amorphous film with a transition layer exhibited better coordination ability with the substrate deformation and higher load-bearing capacity.By controlling the distance between the carbon target and the Mo target, the amorphous carbon films with different Mo contents were prepared by the unbalanced magnetron sputtering equipment (5.5,8.6,29.6,2.7 at%, respectively). It is found that different doping ratio has a profound influence on the surface morphology, meanwhile, both the doping of low and high proportion exhibited higher hardness and lower friction coefficient, but the doping of low proportion showed better wear resistance compared to others. The 2.7% doped a-C film exhibited the best comprehensive properties. The hardness, friction coefficient and the wear rate under the load of 0.2 N in bovine calf serum solutions of the 2.7% doped a-C film were 0.95 GPa、0.035 and 1.39×10-14 m3 N-1 m-1, respectively.