Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
agent. The copper salt was explicitly designed to promote the formation of a protective tribofilm, reduce surface temperature at asperity contacts, and interfere with hydrogen ingress—all according to the hydrogen wear mitigation hypothesis discussed earlier.
Post-test analysis: Surface and subsurface investigation
After completing test run (run off set at 200 million contact cycles), the rollers were sectioned and subjected to detailed post-test analysis using surface microscopy and subsurface serial sectioning—the gold standard for detecting WECs and WEAs.
Surface inspection began with optical microscopy, which identified visible pitting or material disruption. Subsurface evaluation followed a serial grinding and polishing protocol, exposing sequential cross-sections of the roller at 0.1 mm intervals across the wear track. Each slice was etched with Nital and then examined under a metallurgical microscope to reveal any signs of white etching features, crack networks, or changes in microstructure.
This thorough examination allowed the researchers to distinguish between surface-initiated pitting, subsurface cracking, and full-fledged WEC networks. The goal was to detect wear and understand its origin, propagation path, and relationship to the test environment.
What the results revealed The results from the MPR test were conclusive and striking.
Figure 10: Lubricant A post-test inspection
Lubricant A exhibited symptoms consistent with early stage bearing failure as the test progressed. Vibration levels steadily increased—a typical early warning sign of crack formation or pitting initiation within the tribological contact. Eventually, the software automatically halted the test before 75 million contact
34 LUBE MAGAZINE NO.188 AUGUST 2025
The serial sectioning analysis confirmed this. Seven consecutive slices taken at 0.1 mm intervals across the wear track revealed multiple microstructural anomalies: white etching areas, white etching cracks, surface-initiated cracks, and even dark etching areas,
Figure 9: Lubricant A performance data
Post-test inspection of the roller revealed visible pitting across the wear track, with multiple isolated pits observed at both low and high magnification. These pits were not shallow surface abrasions but the result of subsurface crack propagation, consistent with WEC-type failures. The morphology of these features differs from micropitting, which tends to be shallow, surface-initiated, and fatigue-driven. These pits had steep walls and irregular floors, suggesting a deeper, more catastrophic failure mechanism.
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cycles when the vibration exceeded a set threshold, indicating that damage had progressed beyond a tolerable limit.
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