A study on graphite extrusion phenomenon under the sliding wear response of cast iron using microindentation and microscratch techniques

• The interaction between graphite lamellas and abrasive particles is discussed.
• Matrix deformation showed a major effect on lubricating performance of graphite.
• A mechanism on self-lubricating behaviour of graphite lamellas is proposed.
• Under matrix deformation all lamellas are fractured and extruded form the center.

This study focuses on the graphite flakes extrusion mechanism during microindenting and microscratching of cast iron. Observations on the graphite response under abrasive conditions revealed that the matrix deformation which is occurred during a sliding wear condition could have a significant influence on its lubricating performance. Simple microindentation and microscratch tests were conducted to explore the lamellar graphite contribution to tribofilm formation under abrasive wear conditions. The results obtained showed that induced plastic deformation which developed adjacent to the graphite compressed the lamellas and in turn resulting in extrusion of the graphite from its natural position. Further investigations on both indentation and scratch tests indicated that, surprisingly, the graphite began to be fractured and extruded from the centre of graphite lamellas, irrespective of the lamella size. Additionally, a mechanism was proposed to explain the self-lubricating and the extrusion behaviour of the lamellar graphite as a result of indentation.