Study of the tribochemical behavior of Al ion-implanted pure iron lubricated with ZDDP

Abstract

Friction and wear tests of unimplanted and Al ion-implanted pure iron specimens were carried out under lubrication conditions with liquid paraffin or liquid paraffin containing 2 wt% zinc dialkyldithiophosphate (ZDDP). The friction and wear data were analyzed, and the worn surfaces were characterized using Auger electron spectroscopy and X-ray photoelectron spectroscopy. It was found that Al ion implantation, with liquid paraffin as a lubricant, increased the wear resistance of pure iron by a factor of 50–70%. It was considered that the increase in wear resistance was due to the increase in surface residual compressive stress and microhardness induced by the implantation. The existence of oxide (Al 2O 3) film on the surface of the ion-implanted specimen also has a favorable effect on the wear resistance for its antiadhesion and antiscuffing action. When ZDDP was added to liquid paraffin the wear resistance of both Al ion-implanted and unimplanted specimens was enhanced, but the wear resistance of the former was inferior to that of the latter. It was believed that the wear of the specimen was controlled by composition and amount of the antiwear reaction film, and the mechanical strengthening induced by Al ion implantation played a less important role in affecting the wear rate than the tribochemical effects on wear. The existence of Al element in the implanted pure iron retarded the reactions of iron with active elements S and Zn decomposed from the additive, reduced the amount of surface antiwear film formed during the wear process and changed the composition of the films.