Comparison of expanded austenite and expanded martensite formed after nitrogen PIII

The formation of expanded austenite is a well-established phenomenon after energetic nitrogen ion implantation into austenitic steel or nickel alloys, correlated with a very high surface hardness and wear resistance. Using high-voltage PIII implantation into martensitic stainless steels, it is also possible to form expanded martensite. In this work, results are compared for martensitic and austenitic stainless steel. Both groups of materials show a lattice expansion of the base material within the nitrogen diffusion zone of several micrometer at 400 °C. Nevertheless, the expanded martensite exhibits a significantly higher hardness, reaching up to 2000 HV, compared to 1000–1200 HV for expanded austenite. In both groups, a wear reduction of several orders of magnitude is observed. An attempt is made to explain the results within the framework of ion-induced effects.