Search

Low-temperature plasma nitriding of austenitic stainless steel can ensure that its corrosion resistance does not deteriorate, improving surface hardness and wear performance. Nevertheless, it requires a longer processing time. The hollow cathode discharge effect helps increase the plasma density quickly while radiatively heating the workpiece. This work is based on the hollow cathode discharge effect to perform a rapid nitriding strengthening treatment on AISI 304 stainless steels. The experiments were conducted at three different temperatures (450, 475, and 500 °C) for 1 h in an ammonia atmosphere. The samples were characterized using various techniques, including SEM, AFM, XPS, XRD, and micro-hardness measurement. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were employed to assess the electrochemical behavior of the different samples in a 3.5% NaCl solution. The finding suggests that rapid hollow cathode plasma nitriding can enhance the hardness, wear resistance, and corrosion properties of AISI 304 stainless steel. [ABSTRACT FROM AUTHOR]

Ti6Al4V titanium alloys, with high specific strength and good biological compatibility with the human body, are ideal materials for medical surgical implants. However, Ti6Al4V titanium alloys are prone to corrosion in the human environment, which affects the service life of implants and harms human health. In this work, hollow cathode plasm source nitriding (HCPSN) was used to generate nitrided layers on the surfaces of Ti6Al4V titanium alloys to improve their corrosion resistance. Ti6Al4V titanium alloys were nitrided in NH3 at 510 °C for 0, 1, 2, and 4 h. The microstructure and phase composition of the Ti-N nitriding layer was characterized by high-resolution transmission electron microscopy, atomic force microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. This modified layer was identified to be composed of TiN, Ti2N, and α-Ti (N) phase. To study the corrosion properties of different phases, the nitriding 4 h samples were mechanically ground and polished to obtain the various surfaces of Ti2N and α-Ti (N) phases. The potentiodynamic polarization and electrochemical impedance measurements were conducted in Hank's solution to characterize the corrosion resistance of Ti-N nitriding layers in the human environment. The relationship between corrosion resistance and the microstructure of the Ti-N nitriding layer was discussed. The new Ti-N nitriding layer that can improve corrosion resistance provides a broader prospect for applying Ti6Al4V titanium alloy in the medical field. [ABSTRACT FROM AUTHOR]

In direct current plasma nitriding (DCPN), the treated components are subjected to a high cathodic potential, which brings several inherent shortcomings, e.g., damage by arcing and the edging effect. In active screen plasma nitriding (ASPN) processes, the cathodic potential is applied to a metal screen that surrounds the workload, and the component to be treated is placed in a floating potential. Such an electrical configuration allows plasma to be formed on the metal screen surface rather than on the component surface; thus, the shortcomings of the DCPN are eliminated. In this work, the nitrided experiments were performed using a plasma nitriding unit. Two groups of samples were placed on the table in the cathodic and the floating potential, corresponding to the DCPN and ASPN, respectively. The floating samples and table were surrounded by a steel screen. The DCPN and ASPN of the AISI 304 stainless steels are investigated as a function of the electric potential. The samples were characterized using scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffraction, atomic force microscopy and transmission electron microscope. Dry sliding ball-on-disk wear tests were conducted on the untreated substrate, DCPN and ASPN samples. The results reveal that all nitrided samples successfully produced similar nitrogen-supersaturated S phase layers on their surfaces. This finding also shows the strong impact of the electric potential of the nitriding process on the morphology, chemical characteristics, hardness and tribological behavior of the DCPN and ASPN samples. [ABSTRACT FROM AUTHOR]

AISI 420 martensitic stainless steel was treated by active screen plasma nitriding. The test table was placed inside the steel screen but isolated from the cathodic potential. The specimens, together with the furnace wall and test table, were earthed, resulting in formation of anodic potential. Treatments were carried out in NH 3 atmosphere of 400 Pa for 6 h at temperature ranging from 440 to 520 °C. The specimens were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and micro-hardness measurement. The results showed that anodic nitriding treatments were able to produce different types of modified surface layers at different temperatures. The thickness of the nitrided layers and surface roughness increased with the nitriding temperature. Dry sliding wear tests and electrochemical corrosion tests were conducted on the untreated substrate and nitrided specimens. It can be concluded that active screen plasma nitriding at anodic potential improved the hardness, wear resistance, and corrosion properties of AISI 420 stainless steel. [ABSTRACT FROM AUTHOR]

Electron beam melting (EBM) is an additive manufacturing technology that allows flexible processing of parts with complex shapes, but the product surface is usually rough and porous, which affects its corrosion resistance. In this study, the plasma nitriding has been conducted on electron beam melted Ti6Al4V titanium alloy. The samples were analyzed using X-ray diffraction (XRD), optical microscope (OM), scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscope (HRTEM). The results showed that the plasma nitriding-treated EBM sample (PN-EBM) exhibited better corrosion resistance in natural seawater than the EBM sample due to the generation of a ∼16 μm compound layer, which can effectively prevent the intrusion of harmful ions and enhance the corrosion resistance of the EBM titanium alloy. • Electron beam melted Ti6Al4V titanium alloy was surface strengthened by plasma nitriding. • N-rich modified layer with a nitrogen content of 8∼10 wt% composed of TiN and Ti 2 N phases. • Plasma nitriding significantly improve the corrosion resistance of EMB samples in natural seawater environments. [ABSTRACT FROM AUTHOR]

In this work, electron beam melting (EBM) titanium alloy were strengthened by carrying out a hollow cathodic plasma source nitriding treatment. The EBM-TC4 alloys were nitrided at 500 °C for 1, 3, and 5 h in an NH 3 atmosphere. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy was used to evaluate the microstructure and surface morphology of the samples. The nitrided layers formed on the EBM-TC4 alloy were identified as TiN, Ti 2 N, and nitrogen-stabilized α(N)–Ti phases. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements were carried out to evaluate the electrochemical behavior of the samples in Hank's balanced salt solution. The relationship between the corrosion resistance of the nitrided layer and its microstructure was explored. Thus, the improved properties of the nitrided alloys can be attributed to the formation of a Ti–N layer composed of an outermost nanocrystalline/amorphous TiN layer and a crystalline TiN sub-layer on the top of the Ti 2 N crystal layer. The novel Ti–N layer structure with improved corrosion resistance provides broad opportunities for the application of commercial Ti alloys and improving their durability. • HCPSN was used to fabricate a nitrided layer on an EBM-TC4 alloy. • A compound layer composed of an outermost nanocrystalline/amorphous TiN layer and a crystalline TiN sub-layer and on the top of the Ti 2 N crystal layer. • The nitrided layer remarkably improved the corrosion resistance of the EBM-TC4 alloy in Hank's balanced salt solution. • This can be attributed to the formation of a protective multilayer-structured Ti–N layer and its appropriate roughness. [ABSTRACT FROM AUTHOR]

Little work has been reported directly compared to the tribological behavior of plasma nitrided pure titanium and those coated with TiN coatings. This work prepared the compound layers and coatings with the same thickness on TA2 pure titanium by plasma nitriding and multi-arc ion plating. The tribological behaviors of sliding against ZrO 2 balls under lubricant conditions were investigated using a UMT-5 tribo-tester. The results reveal that nitrided and coating samples showed the friction coefficients (0.11–0.12) were significantly decreased compared to that (~0.33) of the TA2 pure titanium matrix. It was also found that the wear mechanism is different after nitriding or coating, which is caused by the surface phases, chemical composition, and surface roughness under other processes. [ABSTRACT FROM AUTHOR]