Importance of surface activation for nitrided layer formation on austenitic stainless steel

Abstract

Gas nitriding of austenitic steel is only possible if the passive oxide layer is removed. Therefore, surface activation forms an important part of the treatment. The main objective of the present study was to investigate the influence of activation on nitrided layer's growth. Various activation treatment methods have been applied -physical (ion sputtering with various current-voltage parameters and gases) and chemical ones (phosphating and chemical etching). The effectiveness of activation has been evaluated after gas nitriding in different conditions of atmosphere composition. The layers have been investigated using transmission electron microscopy, X-ray diffraction and grazing angle X-ray diffraction, magnetic and atomic force microscopy, electron probe microanalysis. Physical activation turned out to be the most effective method. At the same time, it made it possible to reduce the quantity of ammonia in nitriding atmosphere necessary to obtain layers composed of 'expanded austenite'. Moreover, depending on the sputtering parameters and the gas used, it was possible to obtain layers with various kinds of morphology.

Surface Modification of Austenitic Stainless Steel by Means of Low Pressure Glow-Discharge Treatments with Nitrogen

“…In order to allow a homogeneous incorporation of nitrogen during the treatment, the passive oxide film of stainless steels has to be previously removed. This surface activation is the first and fundamental step in the nitriding treatment, and it has been shown that the pre-cleaning procedure and parameters can also influence the modified layers thickness and growth [1,18]. The cathodic sputtering technique, which is usually used as the pre-treatment of plasma nitriding or ion implantation processes, is particularly efficient [18], and it allows both surface cleaning and heating of the samples up to the treatment temperature due to ion bombardment [11].…”

“…This surface activation is the first and fundamental step in the nitriding treatment, and it has been shown that the pre-cleaning procedure and parameters can also influence the modified layers thickness and growth [1,18]. The cathodic sputtering technique, which is usually used as the pre-treatment of plasma nitriding or ion implantation processes, is particularly efficient [18], and it allows both surface cleaning and heating of the samples up to the treatment temperature due to ion bombardment [11]. Pre-treatments using argon [19], hydrogen [18], argon-hydrogen [20], nitrogen [18] and nitrogen-hydrogen [11] were reported, often at pressures lower than 100 Pa; the low pressures cause not only an enhancement of the sputtering effect but also a surface etching [3].…”

“…The cathodic sputtering technique, which is usually used as the pre-treatment of plasma nitriding or ion implantation processes, is particularly efficient [18], and it allows both surface cleaning and heating of the samples up to the treatment temperature due to ion bombardment [11]. Pre-treatments using argon [19], hydrogen [18], argon-hydrogen [20], nitrogen [18] and nitrogen-hydrogen [11] were reported, often at pressures lower than 100 Pa; the low pressures cause not only an enhancement of the sputtering effect but also a surface etching [3]. When nitrogen is used in the gas mixture, its incorporation in the surface layers may occur, depending on treatment parameters [21].…”

Surface Modification of Austenitic Stainless Steel by means of Low Pressure Glow-Discharge Treatments with Nitrogen

“…In order to allow a homogeneous incorporation of nitrogen during the treatment, the passive oxide film of stainless steels has to be previously removed. This surface activation is the first and fundamental step in the nitriding treatment, and it has been shown that the pre-cleaning procedure and parameters can also influence the modified layers thickness and growth [1,7]. The cathodic sputtering technique, which is usually used as the pre-treatment of plasma nitriding or ion implantation processes, is particularly efficient [7], and it allows both surface cleaning and heating of the samples up to the treatment temperature thanks to ion bombardment [8].…”

“…This surface activation is the first and fundamental step in the nitriding treatment, and it has been shown that the pre-cleaning procedure and parameters can also influence the modified layers thickness and growth [1,7]. The cathodic sputtering technique, which is usually used as the pre-treatment of plasma nitriding or ion implantation processes, is particularly efficient [7], and it allows both surface cleaning and heating of the samples up to the treatment temperature thanks to ion bombardment [8]. Pre-treatments using argon [9], hydrogen [7], argon-hydrogen [10], nitrogen [7], and nitrogen-hydrogen [8] were reported, often at pressures lower than 100 Pa; the low pressures cause not only an enhancement of the sputtering effect but also a surface etching [3].…”