Reproducing automotive engine scuffing using a lubricated reciprocating contact

• Published in: Wear 2015-05, Vol.332-333, p.1193-1199
• Main Authors: Kamps, T.J., Walker, J.C., Wood, R.J., Lee, P.M., Plint, A.G.
• Format: Article
• Language: English
• Subjects: Automotive; Automotive engines; Bearing steels; Cast iron; Chromium steels; Cylinders; FIB; Friction; Graphite; Grey cast iron; High speed friction; Lubrication; Ramps; Reciprocating; Scuffing
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2014.12.045

The frequency and severity of scuffing in automotive engines has the potential to increase due to new low-viscosity lubricants for fuel efficiency and increased cylinder power output. This work is to understand the fundamental causes and events resulting in piston ring and liner scuffing. A TE-77 high frequency reciprocating tribometer was used with a synthetic PAO base oil (4cSt) to reciprocate a 52100 G5 barrel against a ground pearlitic Grade 250 grey cast iron. Samples were run-in at 50N and 10Hz prior to a temperature ramp to 150°C followed by a discreet load ramp to 1kN (0.49GPa). The tests were terminated when a sharp increase in the average friction force was observed indicating that scuffing had occurred. 3D optical profilometry showed that the scuffed cast iron surface consisted of smeared platelets and craters of 35μm depth. SEM and EDX analyses suggested adhesive transfer of cast iron material to the counter-surface was occurring by failure along lamellar graphite interfaces. Tests were repeated using instantaneous high-speed friction data and indicated that micro-scuffing initiated at a load of 620N. Focused ion beam cross-sections of the mildly scuffed surface confirmed the mechanism of sub-surface crack initiation occurring along lamellar graphite boundaries. [Display omitted] •Scuffing of a ring-liner contact has been simulated on a reciprocating tribometer.•Mild to severe scuffing has been observed for a grey cast iron liner material.•High speed friction data determined the onset of mild and severe scuffing.•Scuffing occurred along the lamella graphite boundaries as shown by FIB and EDX.