Growth of Fe3C-VACNT surfaces by metal dusting under plasma carburizing: Fractional factorial study and correlation with morphological and structural aspects

Abstract

This study investigates the development of surfaces that combine wear-resistance and solid lubrication properties using single low-temperature plasma carburizing treatments associated with the metal dusting phenomenon. The surfaces consisted of a regular cementite (Fe3C) layer and a film composed by vertically aligned carbon nanotubes (VACNT) grown over the carburized layer. For that, specimens of AISI 1005 steel were used as a substrate. A fractional factorial design of experiments was conducted to identify the best processing conditions to achieve the required Fe3C-VACNT surfaces. Morphological and structural aspects of the surfaces were assessed by scanning and transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The results show that the carburizing performed between 600 and 700 °C and with plasma power densities ≥0.30 W/cm2 were effective for developing the bilayer surfaces. A signature of that process was a temporal increase of the plasma current. According to a created statistical model, the most influential experimental parameters in the average power plasma density were output voltage, %CH4 in the gas mixture, and duty cycle. The surfaces were able to reduce the friction coefficient to values down to 0.08 and decrease the wear rate by 25 to 70 %, depending on their characteristics.