TRIBOLOGICAL PROPERTIES OF PISTON RINGS DESIGNEDFOR SLIDING AGAINST COMPOSITE MATERIALSIN LUBRICATED CONTACTS

The paper presents basic information on the production, structure and tribological properties of a compositechromium-ceramic coating deposited electrolytically on a cast-iron piston ring for a combustion enginedesigned for sliding against a composite cylinder liner. The results of comparative tests of two contacts,i.e. cast-iron GJL-250/AlMC and GJL250+Cr-Al2O3/AlMC, are described. The deposition of the Cr-Al2O3coating on the cast-iron piston ring reduces almost trifold the wear of the piston ring and about 20% thefriction resistance in the contact due to the presence of aluminium oxide particles and fibres. The reinforcingphase removed from the chromium layer polishes the chromium and composite sliding surfaces. The placesleft by the removed particles serve as depots for oil, which reduces the friction forces and minimises oilconsumption. The Al2O3 wear debris decreases the roughness of the surfaces in contact, which additionallyreduces the friction forces according to the friction hypothesis of Ernst and Merchant.