Surface morphology and mechanical properties of a microwave plasma assisted chemical vapor deposited micro textured carbide layer on cobalt-chromium-molybdenum alloy used for artificial joints

The reduction of wear for metal-on-metal implantable materials is proposed by the deposition of a micro-textured carbide surface layer (referred to as “brain coral”). Formation of the micro-textured carbide surface has been developed using a microwave plasma-assisted chemical vapor deposition process (MPCVD). The mechanical properties and surface morphology of this surface have been shown to play an important role in its rate and mechanism of wear.;In this study, the elastic modulus, hardness and contact stiffness were determined by nanoindentation techniques. In addition, the micro-hardness of the micro-textured surface was determined using microindentation techniques. The surface profile parameters (Ra, rms and PV and peak area) were measured using a white light profilometer (WLISP). The effect of deposition processing time on the morphology and mechanical properties was also investigated. The WLISP image of the carbide layer surface profile exhibited the brain coral” pattern after 2 hours of deposition time. The 4-hour deposition processing time yielded the optimal surface morphology with a mature “brain coral” surface structure that has an overall surface average roughness (Ra) of 0.55 (± 0.17) μm. In contrast, the peak areas, which include the contacting areas, have an Ra of 0.22 (± 0.09) μm.;The micro-hardness of the CoCrMo alloy, the “as-deposited” and polished micro-textured carbide surfaces were found to be 7.30 (± 0.5) GPa, 10.2 (± 1.2) GPa and 8.21 (1.07) GPa, respectively. The nano-hardness of the polished micro-textured carbide was determined to be 15 (± 4) GPa, in contrast that observed for the native CoCrMo alloy (9 (± 0.3) GPa). The reduced modulus and contact stiffness for the micro-textured carbide surface were 254 (± 18) Gpa and 170 (± 15) GPa. These values are slightly higher than those observed for the CoCrMo alloy. The similarity in the values of reduced modulus for both the carbide layer and the substrate is important in reducing failure due to fracture toughness. Preliminary results suggest that the coefficient of friction (CoF) of micro-textured carbide surface on stainless steel is comparable to steel 1045 on stainless steel. The enhanced mechanical properties and morphological advantages of the micro-textured surface, together with its potential lubricant and debris trapping ability, makes it an attractive material for use in metal-on-metal joint replacement applications.