Tribological behaviour of plasma nitrided 722M24 material under dry sliding conditions

Abstract

The tribological behaviour of plasma nitrided 722M24 was evaluated under dry sliding conditions. The plasma nitrided samples were fully characterized, using metallographic, X-ray diffraction and microhardness techniques, before wear testing. Wear tests were performed on a “Universal” wear testing machine developed by NCT with plasma nitrided AMS 6472 used as the counterface material. The resulting wear loss was monitored as a function of load and test time. Although all the nitriding treatments improved the wear characteristics of the 722M24 material, the level of improvement was related to the temperature and duration of the nitriding treatment. There are specific combinations of case depth and surface hardness which are required to ensure minimum wear loss. Plasma nitriding for 9 h at 550 °C and for 16 h at 570 °C produced the best results in terms of preventing weight loss. Surface hardness is more important than case depth in preventing wear loss. However, a certain thickness of case is necessary to support the hard surface layer. Long treatment times produce lower surface hardnesses and deeper cases which are less effective in preventing wear.