Study of interactions between lubricant components and tribomaterial surfaces

Kartik Pondicherry

Research output: ThesisDoctoral Thesis


The work presented in this doctoral thesis deals with interactions between the three main components of a journal bearing system of an engine, viz., the lubricant, the journal bearing, and the shaft. While tribological investigations to this effect were carried out at model scale on a rotary tribometer with a ring on disc configuration, post-test surface characterization was carried out with the help of several analysis techniques including light microscopy, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX), Atomic force microscopy (AFM), X ray photoelectron spectroscopy (XPS). In the context of this work, three types bearing materials - Al-based, CuSn, and polymer-based - have been tested keeping the material of the shaft, which is steel, constant. However, a handful of experiments have also been carried out with alternative materials such as Ti-, and Ni-based alloys. The primary focus here lay on evaluating the role of lubricant additives such as zinc di-alkyldithiophosphate (ZDDP) under the current contact conditions, wherein the nominal contact pressures are less than 5 MPa. These additives are known to be very effective under Hertzian contacts with pressures close to two orders of magnitude higher, through formation of surface films known as tribofilms. Based on the information gathered from tribometric investigations and the subsequent surface characterization, presence of various interactions between the lubricant additives and the tribosurfaces has been determined. The first and foremost being formation of tribofilms on select regions of the surface of steel and also on selective secondary hard phases of the bearing materials such as Al2Cu and Si. The prerequisites for their formation have been elucidated in this work, and it has been observed that they form on a “form when needed” basis. On the other hand, cleavage of ZDDP which leads to tribofilm formation also caused tribochemical reaction at the surface of CuSn bearing material, which led to formation of reaction layers on its surface. These layers, brittle in nature, were found to be detrimental to the performance of the system. However, appropriate changes in the chemistry of the lubricant resolved this issue. Finally, the study also highlighted the need for synergy between the three components of the journal bearing system in order to harness an optimal performance.
Translated title of the contributionUntersuchung der Interaktionen zwischen Schmierstoff Komponenten und tribologischen Oberflächen
Original languageEnglish
  • Grün, Florian, Assessor A (internal)
  • Ebner, Reinhold, Assessor B (external)
Publication statusPublished - 2012

Bibliographical note

embargoed until null


  • Trobology
  • Large Area Conformal Contacts
  • ZDDP
  • Tribofilms
  • Non-Ferrous Bearing Materials

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