Tribological And Wear Properties Of AISI316 Austenitic Stainless Steel By Plasma Nitriding At Anodic Potential

The anodic plasma nitriding method is used to modify the AISI316 austenitic stainless steel in this paper to avoid the problems such as "edge effect" and "hollow cathode effect" produced by traditional plasma nitrding. Processing temperature ranges from 400℃to 550℃, processing pressure are 500Pa and 800Pa, and the nitriding time is 5 hours. The phase composition, the compound layer thickness and the surface morphology of the nitrided layer, as well as its surface hardness, were investigated using X-ray diffraction (XRD), optical microscopy (OM) and microhardness tester. The thickness of the nitrided layer increased as the nitrided temperature increased. The nitrided layer consists of singleγN phase from 400℃to 490℃, the microhardness of the nitrided layer is measured to be 890HV0.025 at 490℃, CrN phase appears in the nitrided layer when temperature reaches 520℃, theγN phase resolves to CrN+αphase as the temperature is 550℃and the microhardness reached 1190HV0.025.Tribological properties of nitrided and untreated AISI316 austenitic stainless steel was investigated using ball-on-disc tribometer against GCrl5 ball, and the normal loads are 5N, 10N and 15N, the sliding speed are 0.18 m·s-1,0.27 m·s-1 and 0.35 m·s-1 respectively, and the sliding time is chosen to be 120min. The section profile of the worn track is observed by confocal laser scanning microscope (CLSM), the morphology of the worn track and the wear mechanism is investigated using the scanning electron microscope (SEM). As the normal load increases, the depth of the worn track becomes more and more deeper, adhesion, plough and obvious plastic transformation are found in the worn track of the original samples; the worn track of samples nitrided at 490℃and 550℃is shallow, and there is no obvious change in the surface morphology of the worn track. When the sliding speed increased from 0.18 m·s-1to m·s-1, the depth of the worn track of the original is more and more shallower, and plastic transformation is observed in the edge of the worn track; the worn tracks of samples nitrided are also shallower than that of the original samples. It can be indicated that the anodic plasma nitrided AISI316 austenitic stainless steel has shown an obviously improved wear resistance. Wear of the untreated AISI316 austenitic stainless steel is sever characterized by strong adhesion, abrasion, plastic transformation and oxidation mechanism, whilst the anodic nitrided samples was mild and dominated by adhesion, oxidation and mild-abrasion.