Friction and wear behaviour of boron based surface treatment and nano-particle lubricant additives for wind turbine gearbox applications

Gears and other mechanical assemblies are some of the key components for conversion of wind energy to electrical energy in wind turbines, but their durability and efficiency are severely impaired by some tribological issues like micro-pitting, wear, scuffing, and spalling. To address these issues, in this study, a combinational approach is proposed to incorporate surface treatment (electrochemical boriding) in coordination with the use of nano-colloidal lubricant additives. Boron nitride based solid lubricants were manufactured and flat gear steel samples were borided using a novel electrochemical boriding process. Combinations of nano-colloidal lubricant additives and borided surfaces are tested for their tribological performance, mainly friction and wear, over a wide range of contact conditions using a sliding contact linear reciprocating rig. Post-test surface analyses were carried out to investigate tribochemical interactions of colloidal lubricants with the steel surface and the chemical characterization of the tribofilms was investigated using XPS (X-ray Photoelectron Spectroscopy). Wear was also characterized and measured using optical profilometry. The borided surfaces enhanced the mechanical properties of the surface layer, leading to improved wear resistance. Moreover, it was observed that boron nitride stayed well dispersed within the oil and formed a stable tribofilm which was important to achieve improved tribological performance. The results of this current investigation are expected to aid in ongoing research efforts aimed at prolonging durability and efficiency of drivetrain components in advanced wind turbines.