Wear damage and effects of graphene-based lubricants/coatings during linear reciprocating sliding wear at high contact pressure

• Published in: Wear Vol. 400-401; pp. 144 - 155
• Main Authors: Mishra, Dewika, Sonia, Farjana J., Srivastava, Dinesh, Ganesha, G.N., Singha, Utpal, Mukhopadhyay, Amartya
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-04-2018; Elsevier Science Ltd
• Subjects: Additives; Boundary lubrication; Chipping; Coating effects; Coefficient of friction; Cold pilgering; Contact pressure; Crack initiation; Crack propagation; Cylinder liners; Damage; Deformation mechanisms; Extreme pressure lubricants; Extrusion; Frictional wear; Graphene; Graphene-based lubricants; High contact pressure tribology; Lubrication; Mineral oils; Pilger mill; Reciprocating; Sliding friction; Studies; Surface roughness; Tribology; Tubes; Ultrasonic testing; Wear; Zircaloys (trademark); Graphene-based lubricants; Cold pilgering; Lubrication; Wear; High contact pressure tribology
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2017.12.024

The present study reports on the ‘wear damages’ caused at inner surfaces (and sub-surfaces) of extruded zircaloy-4 tube specimens (as half cylinders) during interactive linear reciprocating sliding against outer surfaces of D2 steel half cylinders for different durations (up to 120s) at high contact pressures (of ~ 1GPa) in the absence/presence of mineral oil lubricant (having chlorinated extreme pressure additives) and graphene-based lubricants/coatings [viz., CVD-grown films of well-ordered few layers graphene (~ 7 layers) and thicker graphite (~ 1400 layers)]. The tests were conducted using a custom-made friction-and-wear tester, which also replicates the conditions (in terms of contact geometry, pressure, stroke length and frequency) relevant to the tribological phenomena occurring at the inner walls of tubes subjected to cold pilgering process. Even though none of the lubricants/coatings had any effect on coefficient of friction, presumably because of ‘boundary lubrication’ at such high contact pressures, only the graphene-based lubricants/coatings slowed down the evolution of surface roughness and wear damage. Observations of worn (top)surfaces and cross-sections indicate that ‘wear damages’ at such contact pressures are primarily caused by severe sub-surface deformation and defect/crack initiation/propagation, followed by lateral chipping/delamination; which could be suppressed by the graphene-based lubricants/coatings (but not by the oil-based lubricant).
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•Wear damage at very high contact pressure (~ 1GPa) studied by design-cum-fabrication of friction-wear tester.•Tester replicates all conditions relevant to tribological phenomena during cold pilgering.•Conventional oil-based, as well as graphene-based, lubricants ineffective towards COF (= > ‘boundary lubrication’).•Wear damage at such high contact pressure primarily due to sub-surface cracking, followed by delamination.•Graphene-based lubricant, but not oil lubricant, effective towards suppressing such wear damage.