Effect Of Zero-Sap Antiwear/EP Lubricant Additives On Nano-Mechanical Properties Of Tribofilms Formed On AISI 52100 Steel Grade

Abstract

Numerous nations have recently passed stricter environmental legislation due to excessive release of harmful emissions like sulfur (S), phosphorus (P), and zinc (Zn) in conventional lubricating oil additives used in contemporary internal combustion engines. Use of borate ester lubricant additives with no sulfated ash, phosphorus, or sulfur effect (zero-SAPS) is one way to reduce this effect. The resistance of tribofilms from oils containing borate esters on AISI 52100 steel grade to plastic deformation is not entirely understood, yet. This study compares Zinc Dialkyl Dithiophosphate (ZDDP) to the tribological performance and Nano-mechanical behavior of tribofilms made from each of the antiwear/extreme pressure borate esters in Polyalphaolefin (PAO6) base oil. According to tribological test findings on a reciprocating steel pin-on-steel plate sliding rig, the boundary films formed by the borate esters reduced friction and wear in a manner similar to that of ZDDP. On the wear scar, the Nano-indentation technique was used to characterize the Nano-mechanical properties of the tribofilms. The ratios of reduced elastic modulus to hardness (E’/H) for the tribofilms of both borate esters are not only higher than the steel substrate but also comparable to ZDDP. This shows that boron-containing tribofilms offered ZDDP-like tribological performance and also have the ability to release absorbed frictional energy when moving across elastic asperity contacts. Consequently, using borate additives in lubricating oils in IC engines is a method of reducing exhaust emission modern vehicles without adversely affecting tribological performance.