As specific applications of ion implantation to surface modification, nitrogen ion implantation was applied to S45C, a steel widely used for machine structural applications, to SCM 440 thermally refined steel, and to SCM 415 carburized steel, and their friction and wear characteristics were examined. The results can be summarized as follows
1) In an effort to improve the seizure resistance of SCM 415 carburized steel, investigation centered on a certaining the friction behavior of the nitrogen-ion-implanted surface layers using a Favill Le Vally friction testing machine. It was found that under unlubricated sliding friction, the effect of carburizing treatment in the preceding step was great. Under lubricated sliding friction, however, the load vs. friction coeffient curve for SCM 415 with nitrogen ion implantation was similar to that without, the load at which seizure started was 2000kgf or more, and higher loads could be withstood if ion fluences were increased.
2) The wear volume of the steels subjected and not subjected to nitrogen ion implantation in 1) above was measured to determine their wear characteristics. Since the modified layer of the implanted steels was thinner than that of the gas-nitrocarburized steel, they tended to suffer greated wear at short friction distances. When a modified layer existed, however no great difference in wear resistance was observed between the two kinds of steel.
3) Using a pin-ring-type wear testing machine, a series of lubricated sliding wear tests were carried out on thermally refined steel and thermally refined nitrogen-ion-implanted steel under conditions under which adhesion and thermal wear occur. It was observed that the nitrogen-ion implanted steel had a lower specific wear volume than the thermally refined steel.
4) Analysis of the nitrogen-ion-implanted surface layers and observation of the friction surfaces suggest that the improvement in seizure resistance and wear resistance with nitrogen ion implantation is attributable to the formation of iron nitride ε-Fe2-3
N or higher iron nitride ζ-Fe2
N due to the concentration of nitrogen ions in the surface layer, and that these iron nitrides have a substantial lubricating effect.