Date of Graduation

5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Microelectronics-Photonics (PhD)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor/Mentor

Malshe, Ajay P.

Committee Member

Salamo, Gregory J.

Second Committee Member

Spearot, Douglas E.

Third Committee Member

Tian, Z. Ryan

Fourth Committee Member

Nair, Arun K.

Fifth Committee Member

Wise, Rick L.

Keywords

Lubrication; Surface Characterization; Surface Texture; Tribofilms; Tribology

Abstract

The objective of this research was to understand the evolution of surface texture under boundary/mixed lubrication (BL). Significant material/energy losses occur during BL because of direct contact between the two surfaces. Traditionally, tribofilms have been studied extensively for BL while textures have been used as a static engineering design parameter to enhance lubricant film properties. However, texture is dynamic at the tribological mating interface, where both physical and chemical interactions are continuously modulated. The evolution and the interplay between the tribofilm and texture is least studied in the literature, which is the focus of this research.

MoS2-based lubricants, known for their excellent anti-friction and anti-wear performance [1]–[3], were used during the experiments. The experiments were divided into two parts;

1) polished steel discs were used to study directed organization/re-organization of surface asperities in correlation with tribofilm; 2) textured discs were used to study the effect of artificial texture on manipulation of tribofilm properties. Three stages of lubrication evolution, namely break-in, development, and steady-state, were discovered and studied experimentally. Surface texture was characterized using laser scanning microscope. Tribofilm morphology and chemistry was studied using scanning and transmission electron microscopy and Raman spectroscopy.

The results showed that the surface roughness increases during break-in period and then stabilizes. Addition of directional texture results in early onset and stabilization of tribo-chemical reactions. Raman spectra confirmed presence of MoS2, FeS2, Fe2O3, and molybdate compounds, consistent with previous studies. [3] Cross-sectional TEM images revealed presence of stored lubricant in valleys while delivering lamellar tribo-layer on asperities.

From the results, the following lubrication mechanism was discussed. Initially, during the break-in period, contact between mating surfaces results in re-organization/re-alignment surface asperities under the applied load and directional motion. Creation of fresh asperities in the presence of lubricant along with energy dissipation is responsible for the onset of tribo-chemical reactions. Subsequently, during the development stage, progressing reactions between surface asperities and lubricant lead to formation and stabilization of tribofilm. Eventually, in the steady-state, stabilized texture and tribofilm results in stable lubrication response. The findings of this research will benefit heavy-duty industrial applications involving low-speed, high-load conditions.

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