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TECHNICAL PAPERS

Ultra Mild Wear in Lubricated Tribology of an Aluminium Alloy

[+] Author and Article Information
Sarmistha Das, K. Varalakshmi

Department of Mechanical Engineering, Indian Institute of Science, Bangalore—560012, India

V. Jayaram

Department of Metallurgy, Indian Institute of Science, Bangalore—560012, India

S. K. Biswas1

Department of Mechanical Engineering, Indian Institute of Science, Bangalore—560012, Indiaskbis@mecheng.iisc.ernet.in

1

Corresponding author.

J. Tribol 129(4), 942-951 (May 20, 2007) (10 pages) doi:10.1115/1.2768615 History: Received March 28, 2006; Revised May 20, 2007

Flat faces of steel pins were slid on an eutectic aluminium silicon alloy under lubricated condition in the 1100MPa mean contact pressure range and 0.2ms sliding speed. Two transition in wear rate were observed, at 10MPa and 70MPa. The wear rate in the 110MPa regime was found to be very small and within the measuring instrument resolution and also insensitive to contact pressure. The regime is designated ultramild wear. Lack of plastic flow, minimal fragmentation of silicon particles, and the presence of undistorted voids on the fractured and unfractured silicon particles in the subsurface suggest that the state of stress in the near surface region is elastic. Contact mechanical calculations demonstrate that at contact pressures <13.7MPa, the system is likely to shakedown to an elastic state.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the FIB trench position on the wear track: (a) trenches made directly on the wear track and (b) trenches made on a plane perpendicular to the wear track

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Figure 2

(a) Steady-state wear rate as a function of mean contact pressure indicating three wear regimes: ultramild wear, mild wear, and severe wear, and (b) expanded view to show mild wear regime more explicitly. The straight line is a least-squares fit of wear data in the mild wear regime. All experiments were repeated three times. Only in the severe wear region a standard deviation of more than ±0.01μm∕m in the wear rate was observed. All experimental data shown are averages.

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Figure 3

Friction coefficient in the ultra-mild wear regime. Laps of sliding is the number of times the disk makes contact with the pin.

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Figure 4

SEM micrographs: (a) surface feature of a sample slid in the ultramild wear regime (mean contact pressure=0.32MPa), (b) surface feature of a sample slid in the severe wear regime showing pile up and ratcheting, mean contact pressure=114.64MPa, and (c) typical subsurface feature in the severe wear regime

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Figure 5

Cast microstructure, as ground: (a) optical micrograph showing Si particles distributed in the form of plates or needle shaped and in blocky form and (b) FIB image showing channeling contrast area revealing subgrains

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Figure 6

(a,b) FIB images of the subsurface of a run-in sample, mean contact pressure=0.3MPa, unlubricated, showing different features

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Figure 9

FIB images of subsurface of a sample generated in severe wear: (a) an area shows fragmented silicon particles upto a depth of 30μm and (b) an area shows fragmentation and displacement of silicon particles and flow and deformation of grains

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Figure 8

FIB images of the subsurface generated in the mild wear regime: (a) an area shows voids in the as-cleaved regions of silicon particles and on the unfractured silicon surface, (b) an area shows fragmentation and displacement of Si-particles, a void is seen at a depth of 8μm, (c) an area shows incipient delamination cracks, and (d) signatures of ductile fracture in a delaminated area

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Figure 10

Wear characteristics of aluminium −23% Si alloy slid against steel under dry conditions in a pin-on-disk machine (30). Shows the superposed estimated (presently) elastic shake down limit. σ is the standard deviation of the experimental scatter.

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Figure 7

FIB images of a ultra-mild wear sample (mean contact pressure=0.32MPa): (a) one area of the subsurface which shows mechanically mixed layer, (b) one area of the subsurface that shows voids at the Al-Si interface when silicon is unfractured and in the cleaved gap in fractured silicon particles

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