Towards the deposition of tetrahedral diamond-like carbon films on hip joints by femtosecond pulsed laser ablation

Compared to conventional nanosecond laser ablation, femtosecond pulsed laser deposition (PLD) allows the production of higher energy ions (up to a few keV) in the plasma plume, which strongly affect the structure and properties of the deposited films. In this work, tetrahedral diamond-like carbon (ta-C) films have been deposited by femtosecond PLD on various substrates, including 316L stainless steel, in order to extend the wear resistance of materials used for hip joint replacement. The deposition process has been optimized to obtain smooth and wear-resistant carbon films by ablating a graphite target in ultra-high vacuum conditions at room temperature, with a laser fluence (energy density) ranging from 1 to 6 J cm −2. In situ sputter cleaning of the substrates in an argon atmosphere prior to carbon deposition has been widely investigated: tensile tests show that the adhesion of the films on stainless steel substrates is remarkably enhanced by removing the contamination and oxidized top-coats. The films exhibit high wear resistance (in the 10 −8 to 10 −9 mm 3 N −1 m −1 range) with moderate hardness (in the 20–30 GPa range), which may be favorable for the accommodation motion between contacting surfaces in a hip joint. The ability of these films to satisfy the biomedical requirements is discussed and the possibility to deposit homogeneous ta-C films on a 22.2-mm diameter hemispherical surface is examined. Finally, homogeneous films have been deposited on a 316L stainless steel femoral head, whose wear behavior will be quantified using a walking simulator during several millions of cycles (corresponding to the human activity during several years).