Tribological behavior of gray cast iron textured by maskless electrochemical texturing

Gray cast iron is widely used in diesel automotive engines due to its combination of low cost and good fusibility, but also to the presence of graphite flakes in their microstructure. Besides their role as mechanical dampers, graphite flakes can act as solid lubricant, reducing friction and wear of moving components. Surface texturing has been intensively investigated in recent years to improve lubrication and reduce friction and wear in tribological applications, but little attention has been given to surface texturing of gray cast irons. On the other hand, surface texturing adds costs, which can supplant the benefits achieved, in particular when high cost surface texturing techniques are employed. Maskless electrochemical texturing (MECT) is a promising technique, which combines simplicity, low cost and high speed. Recently, MECT was adapted to texture gray cast irons. This work investigates the tribological performance of gray cast iron textured by MECT using lubricated block-on-ring tests under two different rotational speeds and a constant normal load. The blocks consisted of textured cast iron and the rings of SAE 4620 steel. For comparative purposes, untextured polished gray cast iron blocks, as well as gray cast iron blocks subjected to electrochemical polishing (employing the same electrolyte used during MECT) were tested. The results showed a large reduction in friction (up to 2.5x) and wear (higher than 5x) when comparing the polished and the textured samples. Comparing the textured samples and the electropolished samples, this improvement in performance reduced, showing that the benefits were partly due to the texture pattern itself (arrays of pockets) and partly to the exposure of the graphite flakes during electrochemical dissolution of the metal matrix. As the wear progressed and the contact between the block and the ring became more conformal, the benefits obtained by MECT (and electro polishing) were reduced.