In the case of devices intended for permanent implantation, such as hip, knee and shoulder replacements or dental implants, a highly developed surface promotes the osteointegration process. In contrast, removable implants require a mirror-like surface to prevent tissue ingrowth and allow for non-invasive removal. The objective of this study was to analyze the influence of substrate pretreatment and the properties of DLC (diamond-like carbon) and Si-DLC (silicon-doped diamond-like carbon) coatings, including surface roughness, adhesion, chemical structure, and corrosion resistance. Surface preparation methods such as sandblasting and polishing, commonly used by implant manufacturers, and RFPACVD plasma modification of Ti6Al4V, a popular titanium alloy in the medical field, were used in the study. The results obtained show that regardless of the pretreatment method used to determine the characteristic roughness of the samples, they can be effectively modified with carbon coatings, both with and without silicon doping. Using Raman spectroscopy, it was shown that the pretreatments applied prior to the coating preparation processes did not affect the chemical structure of the coatings prepared within the same group. However, the chemical structures of the DLC and Si-DLC coatings differed. The application of silicon doping in the carbon coatings improved their adhesion to the surface, as did the application of a surface pretreatment by an etching process. Regardless of the surface preparation method, the carbon coatings primarily reduced the electroactivity of the surface, while the silicon doping present in them had a positive effect in shifting the corrosion potential to more positive values.