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Research Papers: Coatings and Solid Lubricants

Wear Evaluation of Engine Piston Rings Coated With Dual Layer Hard and Soft Coatings

[+] Author and Article Information
Vikram Kumar, Avinash Kumar Agarwal

Department of Mechanical Engineering,
Indian Institute of Technology Kanpur,
Kanpur 208016, India

Sujeet Kumar Sinha

Department of Mechanical Engineering,
Indian Institute of Technology Delhi,
New Delhi 110016, India
e-mail: sks@mech.iitd.ac.in

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received March 21, 2018; final manuscript received October 11, 2018; published online November 21, 2018. Assoc. Editor: Sinan Muftu.

J. Tribol 141(3), 031301 (Nov 21, 2018) (10 pages) Paper No: TRIB-18-1120; doi: 10.1115/1.4041762 History: Received March 21, 2018; Revised October 11, 2018

The main objective of this investigation is the evaluation of the performance of hard diamond-like-carbon (DLC) or tungsten carbide (WC) and soft (epoxy composite) dual-coatings on the internal combustion (IC) engine piston rings as a protective coating to reduce their wear. The rings were coated with DLC or WC by physical vapor deposition (PVD) method and then soft polymeric composite coating (epoxy/graphene/base oil SN150) was applied on the hard coating. The tribological tests of the dual-coated piston rings were conducted for 3.6 × 105 cycles at 1500 rpm engine speed and 50% rated load of a diesel engine in order to evaluate the wear performance of the piston rings. Scuffing of cylinder liner and piston rings interface was prevented by the application of polymer composites over the hard-coated rings. DLC hard and soft polymer composite dual coating over the top piston ring was found to have the lowest wear rate 1.69 × 10−12 mm3/N·m compared with the wear rate of dual coatings on the middle and lower rings.

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References

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Figures

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Fig. 1

Modified Stribeck curve and different regimes of lubrication of IC engine components under sliding motion (a generic graph based on Ref. [9])

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Fig. 2

Schematic of the cross section of the cylinder liner and piston ring contact in a diesel engine

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Fig. 3

Schematic (not to scale) of dual coatings over the top surface of the ring

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Fig. 4

Schematic of the engine experimental setup

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Fig. 5

Thermogravimetric analysis results of epoxy/graphene/SN150 composite coated over the surfaces of hard-coated piston rings, before and after the engine test. Figures 5(a) and 5(b) show variations of weight loss and heat flow with temperature, respectively.

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Fig. 6

FTIR of EGNSN composite: (a) before the engine firing test (lowest black color curve), and (b) top ring with DLC intermediate layer, (c) top ring with WC intermediate layer, (d) middle ring with DLC intermediate layer, and (e) lower ring with DLC intermediate layer after the engine firing test

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Fig. 7

(a) Variations in CoF with time (s) and (b) sample images and arrow shows sliding direction, of dual-coatings, DLC/EGNSN, and WC/EGNSN when tested in dry condition and in the presence of base oil lubricant

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Fig. 8

Schematic of the piston ring, worn surfaces of uncoated rings, worn surfaces of dual coating (DLC or WC over-coated with epoxy/graphene/SN150) of piston rings after the test: (a) XY profile of worn surfaces of WC/EGNSN coating on the piston ring, (b) worn surfaces of WC/EGNSN coated rings, (c) XY profile of worn surfaces of DLC/EGNSN coating on the piston rings, and (d) worn surfaces of uncoated and DLC/EGNSN coated rings. Arrows show the position of the piston rings where wear took place in the firing engine test.

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Fig. 9

Three-dimensional surface profiles of the dual coatings: (a) DLC/EGNSN and (b) WC/EGNSN after the engine wear test

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Fig. 10

Wear rates of uncoated and epoxy composite coatings on hard-coated piston rings. Dual coatings on the lower ring delaminated hence wear rate data is not included. The data for uncoated specimen are for the wear of the metal part, whereas those of dual coatings are for the top polymer composite layer. There was no wear to the metal substrate in the case of dual coatings except for the lower ring.

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Fig. 11

Dual-coated (a) DLC/EGNSN, (b) WC/EGNSN top piston rings images after firing engine test, and (c) ring types

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Fig. 12

Worn surfaces of dual-coated (DLC/EGNSN and WC/EGNSN) piston rings after the firing engine test. Top ring coatings were intact and no visible wear or scratching took place. Middle ring coatings showed partial wear at some places. Lower ring showed higher wear compared to the middle ring. Between the two coatings, DLC/EGNSN exhibited superior performance.

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Fig. 13

SEM micrographs of top piston rings coated with (a) DLC/EGNSN and (b) WC/EGNSN dual coatings, after the firing test of the engine

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