Tribological behavior of a multi-walled carbon nanotube coated porous ti-ta shape memory alloy.

Abstract

The improvement of the unique tribological characteristics (self-lubricating and load-bearing capacity) of multi-walled carbon nanotubes (MWCNTs) coated on various shape memory alloys (SMAs) is demanded various practical applications. In this study, the surface of porous Ti-30 at.% Ta (Ti-Ta) SMAs were coated with functionalized MWCNTs (thickness 22.5 ± 0.2 μm) using the electrophoretic deposition method and characterized. First, powdered MWCNTs were dispersed in a solution containing 62:21:17 ethanol to acetone to water to coat the SMAs. Next, the mixture pH and electrophoretic deposition voltage were varied to customize the coating quality. A pH of 7 and a voltage of 40 V was optimal. Scan Electron Microscope micrographs of the SMA-coated surface revealed the homogeneous distribution of the MWCNTs. As shown by the pull-off analysis, the coating strongly adhered to the alloy surface (strength of 7.27 MPa without appreciable delamination). The tribological characteristics of the resulting Ti-Ta SMA surface were enhanced due to the MWCNT coatings. In wet conditions, the uncoated and coated SMA displayed nearly similar coefficients of friction (CoF). However, under dry sliding conditions, the CoF of the coated SMA was much lower (0.06) than the CoF of the uncoated SMA (0.16). In addition, the MWCNT-coated SMA showed excellent wear resistance in the contact modes: the coated alloy surface exhibited an almost tenfold lower rate of wear (0.0083 mm3/Nm) than the uncoated surface (0.0313 mm3/Nm) under dry conditions. Conversely, the wear rate of both the uncoated and coated alloy surfaces under wet conditions was comparable. The proposed MWCNT-coated Ti-Ta SMA surface obtained using the electrophoretic deposition method has great potential for diverse tribological purposes.