Densification, hardness and tribological characteristics of MWCNTs reinforced Ti6Al4V compacts consolidated by spark plasma sintering

The influence of multi-walled carbon nanotubes (MWCNTs) on the densification, hardness and tribological properties of Ti6Al4V was investigated in this study. 1, 2 and 3 wt% MWCNTs were dispersed in Ti6Al4V by high energy ball milling (HEBM) and the milled powders were consolidated by spark plasma sintering (SPS) at temperatures ranging from 850 - 1000 °C. The applied pressure, heating rate and holding time were kept constant at 50 MPa, 100 °C/min and 5 min respectively during processing. The as-received Ti6Al4V, MWCNTs, milled powders and the consolidated compacts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Dry sliding wear tests were conducted at three load levels of 5, 15 and 25 N on the Ti6Al4V and the Ti6Al4V/MWCNTs compacts sintered at 1000 °C using the ball-on-flat tribometer configuration with tungsten carbide (WC) as the counterface material. Wear scars and debris were also characterized by SEM and energy dispersive X-ray spectrometry (EDX) techniques. The relative density of the Ti6Al4V/MWCNTs compacts was improved with increased sintering temperature but declined with increased MWCNTs additions to Ti6Al4V. The Vickers microhardness was enhanced when both sintering temperature and MWCNTs content were increased. Wear volume loss and coefficient of friction for the MWCNTs containing compacts were improved over that of the unreinforced Ti6Al4V alloy. The observed wear resistance enhancement had a positive correlation with the extent of MWCNTs dispersion within Ti6Al4V, the interfacial bond strength between Ti6Al4V and MWCNTs, as well as the presence of hard TiC interfacial product. Although the 2 wt% MWCNTs composite had the least observed material loss during wear testing, the Ti6Al4V/1 wt% MWCNTs composite however exhibited the optimal wear resistance and coefficient of friction (COF) performance comparatively among all the investigated composites.