Triboelectrochemical behaviour of a Si3N4–TiN ceramic composite and a titanium alloy commonly used in biomedical applications

In this paper the corrosion and tribocorrosion behaviour of a traditional metallic biomaterial (Ti6Al4V) and a Si3N4/TiN (SN/TiN) ceramic composite are studied and compared during exposures to 1% NaCl and 1% NaCl + 1% lactic acid solutions. Electrochemical impedance spectroscopy (EIS) data collected on Ti6Al4V in both neutral and acidic solution have been interpreted on the basis of a double layer surface oxide film, which is completely removed from the wear track during the sliding tests. Under these conditions, the impedance of the depassivated region dominates the overall electrode impedance. Previous EIS tests performed on SN/TiN evidence that even this material exposed to neutral solution is covered by a double layer film, while a porous monolayer film forms in acid solution. Under pure corrosion conditions, SN/TiN exhibits corrosion rates which are quite comparable to those measured on Ti6Al4V. During tribocorrosion tests the EIS response of the ceramic material does not change much. Its corrosion rates are two orders of magnitude lower than those measured on Ti6Al4V. Profilometer analysis shows that on both materials most of overall tribocorrosion damage is due to mechanical wear. The tests suggest that SN/TiN is a promising biomaterials for applications where sliding conditions occur.