Processing of Co-base/C-nanotubes compound coatings on D2 steel using plasma transferred by arc: Tribological and mechanical performance

Abstract

In this study, compound coatings consisting of Co-based nanostructured filler metals (FM-Stellite 6) and carbon nanotubes (CNTs) were deposited on D2 steel using the plasma transferred by arc (PTA) technique. The coatings were prepared and analyzed in two steps. First, FM-Stellite 6 was mixed with 0.1 and 0.3 wt% CNTs at 120 °C for 72 h to prepare a Co-based xerogel using Pechini's method and then sintered at 1200 °C for 30 min. High-resolution transmission electron microscopy revealed the growth of bar-shaped solids on the surface of the nanostructured FM with 0.3 wt% CNTs (FM-3CNT) as well as Co particle growth inside the CNTs. In the second step, PTA was used to deposit the coating by replying with and without the FM-CNT. Raman spectroscopy indicated that Co3O4 spinel and MW-CNTs were formed on the compound coatings prepared using 0.1 and 0.3 wt% CNTs. A compound coating prepared from 0.3 wt% CNTs (COAT-3CNT) showed excellent tribological performance owing to its low volumetric wear (0.22 mm3) arising from the combination of self-lubrication and high elastic modulus (123.62 GPa) with a low dissipation energy (39.00 %), which contributed to the high contact stiffness (210 N/m). Likewise, the COAT-3CNT coating underwent a decrease in the secondary-dendrite-arm spacing (SDAS) of 6.81 μm owing to dendritic refinement as a result of the high solidification rate.