Tribological performance of halloysite clay nanotubes as green lubricant additives

Nanoparticles have been recently explored as lubricant additives for improving tribological performance of metal-forming tools. Halloysite clay nanotubes (HNTs) are naturally-occurring, low-cost, and non-toxic nanoparticles, making them attractive as green lubricant additives. In this study, HNTs were dispersed at varying concentrations (0.01, 0.05, and 0.10 wt%) within a polymeric lubricant for metal-forming applications. The ITeE-PIB Polish method for testing lubricants under scuffing conditions was conducted with a four-ball tribotester in order to obtain the scuffing load and load-carrying capacity (p(oz)) under extreme pressures (EP), as this method has demonstrated to be sensitive to extreme-pressure additives; a block-on-ring test was used to obtain wear volume loss and coefficient of friction (COF). Surface roughness of worn materials was characterized with an optical 3D-surface measurement system. Results showed that 0.05 wt% HNTs delayed scuffing initiation, and increased the scuffing load and load-carrying capacity by 50% and similar to 72%, respectively. Wear volume loss and COF were both lowered by similar to 70%, and surface roughness was reduced due to the formation of a tribofilm. The improved lubrication provided by environmentally-friendly HNT lubricant additives shown in this study may result in considerable cost savings through lower energy consumption and longer tool life. (C) 2017 Elsevier B.V. All rights reserved.