NITROGEN IMPLANTATION OF STEELS - A TREATMENT WHICH CAN INITIATE SUSTAINED OXIDATIVE WEAR

Mild steels which have been either thermally oxidized near 300 °C or implanted with nitrogen ions have been wear tested using a modified Falex Lubricant Testing machine. Both these treatments cause similar, much reduced wear rates which are about an order of magnitude better than in untreated samples. Specimens worn after treatments by both methods have been examined in detail using scanning electron microscopy and Auger spectroscopy. It is concluded that the wear induced by oxidation is the same as the wear induced by nitrogen ion implantation. Both of these treatments acted to initiate favorable sustained oxide wear and confirm the Initiator/Sustainer model. Additional studies have been done on oxidized samples using a variety of sample processing techniques and sequences including oxide layer stripping, wear recycling, and annealing. These studies clearly show that favorable wear results were caused by the grown oxide layer and not by the heat treatment. Also, it has been found that the favorable oxide wear can be stopped and started numerous times since it is able to reinitiate and sustain itself. However, if a worn oxide layer is stripped from a sample just prior to the wear run, favorable wear does not occur unless the sample was oxidized or favorably worn in the last few weeks. This occurs because wear favorable chemistry at the oxide/metal interface anneals at room temperature. Other discussions of the wear initiating and sustaining processes are presented.