Mechanical Properties of the Stellite 6 Cobalt Alloy Implanted with Nitrogen Ions

Abstract

The effect of nitrogen ion implantation on Stellite 6 cobalt alloy was investigated. In this research, cobalt alloy was implanted with 65 keV nitrogen ions at the fluence of (1 ÷ 10) × 10 16 N + /cm 2 . The distribution of implanted nitrogen ions and vacancies produced by them was calculated using the SRIM program. The surface morphology was examined and the elemental analysis was performed using scanning electron microscopy, energy dispersive X-ray spectroscopy and grazing incidence X-ray diffraction. The wear tests were conducted with the use of the pin-on-disc method. The results demonstrate that implantation with nitrogen ions significantly reduces the friction factor and wear. The friction coefficient of the implanted sample at the fluence of 1 × 10 17 N + /cm 2 increased to the values characteristic of an unimplanted sample after 5000 measurement cycles. The depth of the worn trace was about 2.0 µm. This implies that the thickness of the layer modified by the implantation process is ≈ 2.0 µm and exceeds the initial range of the implanted ions by an order of magnitude. This is referred to as a long-range implantation effect. The investigations have shown that the long-range effect is caused by movement of not only implanted nitrogen atoms but also carbon dopant atoms towards the friction zone. Diffusion of carbon atoms has been documented here for the first time. Furthermore, the increased content of oxygen atoms on the track bottom indicates a dominant oxidative wear of the Stellite samples after nitrogen implantation with the energy 65 keV and the fluences of 5 × 10 16 and 10

Tribological Properties of Stellite 6 Cobalt Alloy Implanted with Nitrogen Ions Determined in the Tests Conducted in Engine Fuel Atmosphere

“…The effect of lowering the friction and wear coefficients after im- plantation observed in the previous work [7] disappears. This can be caused by a lower local friction node temperature due to engine fuel overrun, which reduces the diffusion of nitrogen atoms and the speed of radiation defects moving into the sample.…”

“…When measuring the friction coefficient during a tribological test in the presence of a lubricant there is no such a great difference between the implanted and nonimplanted samples compared to technically dry friction conditions [7]. Compared to the sample that has not been subjected to ion implantation, a slight increase in the friction coefficient for the implanted samples is observed.…”

“…This will probably lead to their lower consumption than in laboratory tests because of a higher working temperature that accelerates the diffusion of nitrogen and causes the radiation defects to move into the material, which will result in reduced wear of the implanted layer. In addition to the inlet valves, despite the presence of fuel on the surface of their seats, there occurs mixed friction -with the advantage of technically dry friction, for which a significant reduction in the friction coefficient and wear was achieved [7]. Preparations for such in-service research have already begun.…”

Cavitation Erosion and Sliding Wear Mechanisms of AlTiN and TiAlN Films Deposited on Stainless Steel Substrate

“…To simulate moderate friction conditions describing mostly limited sliding loads in fluid machinery, the nano-tribo tests were performed with the use of the NTR2 nano-tribometer from Anton Paar GmbH [29,30]. A WC ball with a 0.5 mm diameter was used as the counterpart.…”

Comparing of Microhardness of the Stellite 6 Cobalt Alloy Implanted with 175 keV Mn+ Ions and 120 keV N+ Ions

“…The Kruskal-Wallis test showed statistically significant differences in microhardness of samples implanted with Mn and N ions with doses D=1•10 17 ions/cm 2 with compare to unimplanted sample. In the case of N ion implantation, this can be caused by the formation of nitrogen compounds in the material structure, which is described in the paper [34]. Manganese ion implantation does not cause the formation of new fractions, it is part of a solid solution, which was noted in [30] and the dose of implanted ions was set to D = 5•1016 Mn + /cm 2 and D = 1•1017 Mn + /cm 2 .…”