X-ray spectroscopy study of the effect of passive film composition on plasma nitriding efficiency

Purpose and goal

The transition to using plasma nitriding for high-alloy steel transmission components would enable the production of lighter, high-performance gearboxes. One objective for the project is to offer a very promising technology (HAXPES) to Ovako and Bodycote. Representatives from both companies participated in the measurements and are now well acquainted with the possibilities of this technology. Another objective to understand the causes of passivation effects observed. The results show that the presence of Al2O3 on the surfaces can be an important cause for passivation.

Expected results and effects

The results show the presence of Al2O3 in gear roots before plasma nitration on gears manufactured in H13 and Ovakos Hybridstål. Al2O3 is a very dense oxide and probably has a strong passivating effect on nitriding. The results indicate that Al diffuses to the surface and forms an oxide. Samples in the same steels that were ground and aged at room temperature also showed accumulation of Al on the surface.

Planned approach and implementation

Samples from root and flank in Ovakos Hybridstål and in H13 were cut from gears that were solution treated / quench&tempered and then ground on flanks. In addition to these, samples were also studied in the same material that was ground and then aged at room temperature for various lengths of time, up to 6 months, before the measurements. The HAXPS measurements were performed at P22 beamline, Petra III, in Hamburg with 2.5 keV and 7.5 keV