TRIBOLOGY


Wear performance of different lubricant formulations under varying current intensities and types using tribo-testing


Dr. Ameneh Schneider,


Gregor Patzer, Marie Ausböck, Optimol Instruments


Motivation Electrification in mobility and industrial sectors is introducing new challenges for tribological systems. In electric vehicles (EVs), lubricants are not only required to ensure low friction and wear under mechanical loads but must also manage electrical stresses that can cause electrically induced bearing damage (EIBD). EIBD occurs when voltage potentials across lubricated contacts discharge through the lubricant film, leading to pitting, frosting, or fluting damage. The electrical properties of oils and greases – especially their electrical contact resistance (ECR) – play a decisive role in determining whether arcing occurs and how damaging it is.


By adapting lubricant composition, especially additive and thickener selection, formulators can influence the balance between electrical insulation and conduction, and thus reduce the risk of EIBD.


There is a need for a testing method which integrates dynamic electrical and mechanical loading for reliable formulation screening.


State of the art Recent literature provides important guidance for lubricant formulation in electrically stressed applications:


Conductive additives: Silver nanoparticles (Ag NPs), carbon black, and graphene lower electrical resistance


18 LUBE MAGAZINE NO.190 DECEMBER 2025


and disperse electrical discharge. Ag NPs can reduce pitting by ~50% compared to standard formulations. Thickener types: Polyurea greases are preferred over lithium systems for both performance stability and raw material supply reasons. ZDDP: Widely used as an anti-wear additive, ZDDP increases ECR, forming insulating tribofilms. While beneficial for wear control, this can concentrate discharge energy under certain current conditions.


Experimentation Testing was carried out on the SRV®5 tribometer with an ECR measurement module, enabling application of both alternating current (AC) and direct current (DC) during oscillating tribological tests.


Figure 1: Test chamber of SRV®


5 test setup, right: ECR sensor schema.


The system applies an oscillating motion under a defined load, while simultaneously passing an AC or DC current through the tested lubricant. Real-time ECR measurement enables the correlation of electrical behaviour with tribological performance.


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