Boundary-Lubricated Dynamic-Pressure Sliding Wear Behavior of Grade 250 Cast Iron

Development of robust tribological testing methodologies that exhibit fidelity to application performance are crucial to the implementation of surface engineered material technologies in sustainable engine propulsion technologies. This investigation assesses the influence of the boundary lubrication regime on surface damage accumulation mechanisms of a grade 250 cast iron subject to dynamic-pressure lubricated reciprocating sliding. Dynamic-pressure sliding plate surfaces were manufactured from grade 250 cast iron with a constriction profile designed to achieve a maximum contact pressure of 70.8MPa at a normal load of 417N against a 52100 steel countersurface with a 2 24mm rectangular contact area. Reciprocating sliding at 15 Hz frequency over a stroke length of 25mm immersed in synthetic polyalphaolefin (PAO4) facilitated transitions in lubrication regime over a dynamic pressure range of 8–71MPa. Changes in dynamic contact pressure during fluid film lubrication over a central constriction at zero acceleration manifest a symmetrical profile in the friction coefficient, indicating squeeze film effects were responsible for asymmetrical friction in offset constrictions. This was not observed in boundary lubrication where a constant friction force of 44N indicated independence of contact area and pressures. A greater volume of localized abrasive wear was observed at the high-pressure constriction, similar to bore polishing, causing a decrease in local average surface roughness (Ra) to 0.12 mm. Scanning electron microscopy and<br/>energy-dispersive x-ray analysis suggested an increase in surface oxide formation in regions of high pressure resulting from increased frictional energy dissipation.