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Research Papers: Friction & Wear

Wear Mechanisms of Gray Cast Iron in the Presence of Environmentally Friendly Hydrofluoroolefin-Based Refrigerant and the Effect of Tribofilm Formation

[+] Author and Article Information
M. Wasim Akram

Mechanical Science and
Engineering Department,
University of Illinois at Urbana-Champaign,
1206 W Green Street,
Urbana, IL 61801

Andreas A. Polycarpou

Mechanical Science and
Engineering Department,
University of Illinois at Urbana-Champaign,
1206 W Green Street,
Urbana, IL 61801
Mechanical Engineering Department,
Texas A & M University,
College Station, TX 77843
e-mail: apolycarpou@tamu.edu

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received December 6, 2014; final manuscript received March 21, 2015; published online July 9, 2015. Assoc. Editor: Satish V. Kailas.

J. Tribol 137(4), 041602 (Oct 01, 2015) (9 pages) Paper No: TRIB-14-1303; doi: 10.1115/1.4030711 History: Received December 06, 2014; Revised March 21, 2015; Online July 09, 2015

Hydrofluoroolefin-based refrigerant (2,3,3,3-tetrafluoropropene, namely, HFO-1234yf), which has been developed as an environmentally friendly refrigerant, is proposed as a direct replacement solution in automotive air-conditioning compressor applications. In the present work, the wear mechanisms of this refrigerant using gray cast iron interfaces were investigated under a wide range of operating conditions. A critical velocity was measured from scuffing type experiments, where beyond that maximum interfacial loads did not change significantly with sliding velocity, suggesting a mechanical rubbing-type wear mechanism. Below the critical velocity, scuffing loads decreased almost linearly with sliding velocities. Wear type experiments identified two different wear mechanisms, namely, oxygen-dominating and fluorine-dominating wear, depending on sliding velocities and normal loads. Oxygen-dominating wear mechanism prevailed under low sliding velocities and normal loads. In contrast, fluorine-dominating wear was predominant under moderate sliding velocities and low or moderate loads. The formation of protective tribofilms and their effect on the wear mechanism was used to construct a wear map.

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Figures

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Fig. 1

Tribological samples: (a) gray cast iron disk, (b) gray cast iron flat pin, (c) schematic of pin-on-disk configuration, and (d) photograph and schematic representation showing lubricant supply system

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Fig. 2

Set 1 scuffing experiments: (a) scuffing load versus time and (b) scuffing load versus sliding velocity

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Fig. 3

Set 1 scuffing experiments versus time: (a) COF and (b) subsurface temperature (2 mm below the contact interface)

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Fig. 7

Typical set 2 wear experiments: (a) COF versus sliding distance and (b) wear-rate versus sliding velocity

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Fig. 8

SEM micrographs of the worn samples tested under set 2 wear experiments: (a) virgin sample; (b) 0.6 m/s and 650 N; (c) 1.8 m/s and 250 N; (d) 2.4 m/s and 200 N; (e) 3.0 m/s and 75 N; and (f) 3.6 m/s and 75 N (thick white arrows show sliding direction)

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Fig. 4

Set 1 scuffing experiments versus sliding distance: (a) COF: below critical velocity, (b) COF: above critical velocity, (c) subsurface temp: below critical velocity, and (d) subsurface temp: above critical velocity

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Fig. 5

SEM images of disk samples after set 1—scuffing experiments: (a) 0.6 m/s, (b) 2.4 m/s, (c) 3.0 m/s, and (d) 4.8 m/s (thick white arrows pointing north indicate sliding direction)

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Fig. 6

EDS qualitative surface chemical composition analysis (set 1—scuffing experiments)

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Fig. 10

Wear map indicating different wear mechanisms

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Fig. 9

EDS analysis of the worn samples (disks) tested under set 2—wear experiments

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