Surface Hardness and Abrasive Wear Resistance of Ion-Implanted Steels

Abstract

The hardnesses of nitrogen-implanted steel surfaces have been measured with an abrasive wear technique capable of characterizing surface layers as thin as 25 nm. Treated steel disks and reference disks were abraded with 1–5 μm diamond, and relative wear resistances were calculated from the mass losses. Surface hardness was obtained from a relationship between wear resistance and hardness. The surface of a hardened and tempered carbon steel implanted with nitrogen ions (10¹⁷/cm²) was significantly harder than with other treatments including quench hardening and nitriding. The hardness decreased to the bulk value over a depth corresponding to the initial implantation depth. Nitorgen-implanted stainless-steel surfaces wore faster than un-implanted ones, possibly due to interference with transformation hardening which normally occurs during wearing. This “softening” effect persisted to depths several times the depth of implantation, and may help to explain the reduction of sliding wear produced by the implantation of stainless steels. Analyses by Auger electron spectroscopy indicated nitrogen migrated toward the bulk during wear. Titanium implanted in stainless steel (4.6 × 10¹⁷ ions/cm²) produced a very hard surface with more than 10 times the abrasive wear resistance of the bulk metal.