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Abstract
A route to reducing the wear of the metal counterpart in the friction of meatal against diamond-like carbon (DLC) is to form a lubricating tribofilm on the metal counterface. However, in liquid lubricating conditions, the formation of tribofilm can be influenced by both the lubricating medium and the counterpart material. Here we report the effect of lubricating biomolecule and doping fluorine element on the formation of tribofilm in fluorinated DLC (FDLC)-Ti6Al4V friction system. A group of ball-on-disc frictional experiments with different sliding speeds and normal loads were performed in phosphate buffer solution (PBS) and bovine serum albumin (BSA) solution. The results showed the formation of tribofilm was inhibited by the absorption of biomolecules on the frictional surface, thus improving the friction coefficient and wear of Ti6Al4V counterpart. Doping fluorine into DLC film also can restrain the formation of tribofilm on Ti6Al4V counterface. As a result, tribofilm is difficult to form when Ti6Al4V counterface slides against FDLC in BSA solution. Fluorinated DLC film should be considered carefully for the anti-wear use in body fluid containing biomolecules because it might cause severe wear of the counterpart material.
Highlights
Tribofilm is a thin solid film generated as a result of sliding contact, which is adhered on the worn surface working as a “third body” with remarkable influence on both the friction behavior and the wear performance
Lafon-Placette investigated the tribological behavior of diamond-like carbon (DLC) film in base oil, the results showed that the counterpart nature played a significant role on the wear of tetrahedral amorphous carbon and suggested that elements with a carbophilic character could promote the formation of a heterogeneous carbon-containing tribofilm on the steel surface [5]
When Ti6Al4V slides against DLC in bovine serum albumin (BSA) (Figure 1a), the friction coefficients decreased with the increase in sliding speed and normal load, which was consistent with the results in Kim’s study [17]
Summary
Tribofilm is a thin solid film generated as a result of sliding contact, which is adhered on the worn surface working as a “third body” with remarkable influence on both the friction behavior and the wear performance. In Liao’s study, a graphitic tribofilm formed on the surface of an explanted CrCrMo artificial hip joint, which was generated from biomolecules in the lubricating body fluid and played a role in reducing wear and corrosion [1]. Some particular counter material can generate tribofilm itself, which is called self-lubricating material, such as diamond-like carbon (DLC) film. The tribofilm generated from DLC film, which is usually called transfer film, normally has a graphite like structure and acts as a solid lubricant to reduce friction and wear [3]. Using the self-lubricating DLC film in a lubricating medium is a promising way to minimize the wear. The interaction between DLC film and Coatings 2020, 10, 903; doi:10.3390/coatings10090903 www.mdpi.com/journal/coatings
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