Investigation on the scuffing resistance of ductile cast iron as affected by fine particle bombardment to produce surface hardened layer and micro-dimpled surface

The objective of this paper is to investigate the influence of fine particle bombardment (FPB) on the scuffing behavior of ductile cast iron. Ductile cast iron samples were processed by FPB treatment, in which three injection air pressures (0.2 MPa, 0.4 MPa and 0.6 MPa) were used for given particle flux (8-10 g/s), treatment time (15 s), nozzle diameter (9 mm) and standoff distance (100 mm). Surface morphology, microstructure and hardness of these samples were examined. Step-loading scuffing tests were then performed on a block-on-ring machine, in which the FPB treated ductile cast iron was used for the block and an alloy cast iron without FPB treatment was used for the ring. The test results show that FPB treatment improves the surface hardness of ductile cast iron by nanocrystallization. An increment of injection air pressure would increase the surface hardness through reducing the grain size within the nanocrystalline layer. FPB treatment decreases the friction coefficient through reducing the surface roughness and producing a micro-dimpled surface. The friction coefficient is decreased when increasing the injection air pressure. The scuffing resistance of ductile cast iron depends on surface hardness and friction coefficient; it would be improved through using a higher injection air pressure during the FPB treatment.