Austenitic steels are known for their high corrosion resistance but at the same time have low wear resistance and high interfacial contact resistance (ICR), which limits their application e. g. as bipolar plates in Proton Exchange Membrane Fuel Cells (PEMFC). Plasma diffusion treatment, specially the well-known plasma nitriding, improves the hardness and interfacial contact resistance but mostly worse the corrosion behavior in PEMFC environment.

Aim of this study is to evaluate the less known plasma carburizing as a suitable process for functionalization austenitic stainless steels. For this purpose, a number of processes were executed under specific variation of temperature ranging from 360 °C to 450 °C and duration of 10 to 16 h. The samples were analyzed using x-ray diffractometer, x-ray photoelectron spectroscopy, SEM, Vickers microindentation, potentiodynamic polarization and ICR measurements.

It could be shown that the corrosion current density (1.78 µA·cm^-2) of the treated samples are an order of magnitude lower than those of the reference (17.38 µA·cm^-2). The ICR was also reduced from > 1000 mΩ·cm^-2 down to 31 mΩ·cm^-2. After corrosion, even lower values around 15 mΩ·cm^-2 were achieved. The targets according to DOE ( < 1 µA·cm^-2 and < 10 mΩ·cm^-2) were almost achieved. A comparison to the plasma nitrided samples was also performed and shows the high potential of plasma carburizing.

Keywords: plasma carburizing, s-phase, austenitic stainless steel, corrosion behavior, interfacial contact resistance, bipolar plate

The AA2024-T3 AlClad alloy is an aluminum alloy widely used in the aerospace industry. The AlClad designation refers to the application of a pure aluminum coating on the alloy surface to improve corrosion protection. Although this alloy has satisfactory mechanical behavior and corrosion resistance for use in aerospace applications, the aluminum coating often wears or peels during service, exposing the substrate to the corrosive environment. The objective of this work was to improve the adhesion of the coating to the alloy substrate through fiber laser glazing, where different current values of the pumping diode were used. This treatment aimed to improve the anchorage between the aluminum layer and the alloy substrate, making the structures more reliable and secure. The laser used was a continuous wave ytterbium-doped fiber laser with a wavelength of 1.07 µm, beam quality (M2) equal to 9, minimum beam diameter of 0.1 mm and displacement speed of 50 mm/s. Argon gas was also used to protect the specimens and the lens with a flow rate of 7 l/min. The analyses were performed using methods such as profilometry, pin-on-plate slip wear, nano-indentation, light optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and electrochemical corrosion tests. Based on the results obtained, it was found that the objective of the study was achieved for all glazed specimens when the pumping current exceeded 50%. There was an increase in the metallurgical bonding between coating and substrate and a decreasing surface roughness with increasing diode pump current. In conditions where the laser pump current was between 50% and 70% the corrosion current densities values are similar to the material, without laser glazing, which indicates that the corrosion resistance was not affected in these cases. In this way, specimens with better coating adhesion, surfaces with lower average roughness and greater hardness were obtained. Consequently, less wear was observed while keeping corrosion resistance similar to that provided by the pure aluminum layer.

Different Cr based coatings were deposited over medium alloy AISI 4140 steel in industrial facilities (Oerlikon Balzers Argentina), to improve wear and corrosion resistance in aggressive environments, like the plastic forming industry, and other applications in the aluminum industry. As AISI 4140 is a soft substrate, tests were carried out in two conditions: i) quenched and tempered (Q&T), ii) Q&T plus ion nitriding.

Friction and adhesive wear test were in a carried out in a rotational pin on disk machine using an alumina ball 6 mm in diameter as counterpart. The coatings were characterized by SEM and XRD. The corrosion test consisted in anodic polarization in a chloride solution. Finally, the film adhesion was tested by Rockwell C indentation and Scratch test at constant loads.

Both coatings resulted about 2.7-3 microns width. They presented good adhesion tested with Rockwell C indentation over nitrided substrates but not so good (HF3) for unnitrided ones. In the scratch test the critical load was over 50 N for the CrN but the AlCrN presented some spallation at the same load.

The CrN coatings presented the lower coefficient of friction in the Pin on Disk test at 5 N load. To measure wear loss, 12 N was used in the duplex case, meaning nitrided plus coating. The wear volume was less in the CrN too. In the corrosion test, only the CrN film showed a quasi-passive zone in NaCl solution, meanwhile the AlCrN presented active dissolution.

The observation of the wear tracks and the film microstructure, so as the surface after corrosion, allowed to explain the difference between nitrided and non nitrided substrates primarily, having this last combination a low load bearing capacity. Between both films, some slightly differences between mechanical properties explain the best behavior of CrN.

Micro-arc oxidation (MAO) is a surface treatment applied to valve material to form a multifunctional ceramic coating based on the principle of anodizing. By regulating electrical parameters and adjusting electrolyte composition, the MAO coating has the capability to meet diverse specifications across numerous domains. Among the various MAO process equipment, the bipolar pulse power supply stands out for its flexible process parameters and fast coating growth rate, which is attributed to the introduction of cathodic bias. The incorporation of cathodic bias has been proven to benefit the properties of the MAO coating by reducing the discharging energy and promoting the crystalline transition within the oxide phase of aluminum. However, the impact of cathodic bias in the MAO process is seldom discussed in magnesium alloy applications.

Over the past decade, the forefront of tribological studies has been illuminated by the exceptional properties of graphene, along with other 2D materials and their synergies with various nanomaterials. These cutting-edge nanolubricants have demonstrated unparalleled wear and friction performance across diverse systems. Their remarkable ability to achieve near-zero levels of friction and wear (known as superlubricity), extends even to macroscopic scales in different environments and under moderate to high contact pressures. This positions them as a promising alternative to traditional oil-based lubricants. Despite their impressive performance, the sustained and long-term reliability of these solid nanolubricants under more intricate tribological conditions remains a subject of ongoing investigation. Establishing their credibility as a potential replacement for oil-based lubricants necessitates a deeper understanding of their behavior in complex scenarios.

At Argonne National Laboratory, we have made significant strides in developing various nanolubricants. Our research showcases the attainment of superlubricity on rough steel contacts, even under high contact pressures (~1GPa), in both linear and sliding-rolling contacts as well as at high temperatures in an ambient environment. Furthermore, these nanolubricants exhibit stability over extended periods, enduring 70 kilometers of linear sliding without failure.

Our investigation delves into the role of tribochemistry at the micro/nanoscale and its profound impact on tribological performance at the macroscale. We present compelling examples resulting from collaborations with industry partners, particularly within the automotive sector, focusing on applications such as metal stamping. This progress not only sets the stage for future breakthroughs but also marks a significant stride toward realizing oil-free superlubricity in real-world applications. By doing so, these research efforts make a substantial contribution to the broader mission of decarbonization and offer sustainable solutions for the evolving lubrication industry

Titanium alloys are characterized by high specific strength, formability and corrosion resistance, but poor wear. The high cost of both metallurgical processing of its ore as well as later mechanical working, machining and the need to improve surface hardness by a proper treatment generally limits its wider application to aviation or military industry. The durability of the mechanically or physico-chemically upgraded surface layer depends to the largest extent on its: (i) geometrical irregularities and (ii) microstructure changes in the sub-surface area, which decide on the surface integrity of the material. Optimizing the latter is critical for components being employed in sliding or rolling contact with other parts and are subject to rapid wear resulting in significantly reduced life-times [1]. Hence, this study focuses on the influence of plastic deformation of near surface areas induced by slide burnishing/shot peening followed by sequential gas and plasma nitriding processes on the tribo-mechanical properties of the Ti-6Al-4V ELI alloy.

The Ti-6Al-4V ELI alloy substrates were subjected to heat treatment followed by a sequence of surface treatments like: turning (T), turning + burnishing (T+B), turning + burnishing + gas/plasma nitriding (T+B+GN/PN), turning + shot peening (T+SP), turning + shot peening + gas/plasma nitriding (T+B+GN/PN). Details of the mechanical treatments and gas nitriding parameters were described in our previous work [2,3]. Subsequently, all the substrates modified in this way were subjected to a detailed investigation involving both their phase composition and microstructure characterization as well as assessment of friction coefficient, hardness and sliding wear properties. Preliminary investigations revealed the in-situ formation of a very thin amorphous ‘tribo-layer’ which could prove to be beneficial during tribological contact. The effect of surface mechanical working applied as pre-treatment for the gas and plasma nitriding on the enhancement of tribo-mechanical properties of Ti-6Al-4V ELI alloy will be discussed in detail in the presentation.

1. Philip JT. et al., Friction, 7(6), (2019) 497–536
2. Toboła D. et al., Appl. Surf. Sci., 515 (2020) 145942
3. Toboła D. et al., Appl. Surf. Sci., 602 (2022) 154327

An electroplating method was used to modify the surface morphology of carbon fiber bundles. It deposits a layer of nickel film on the surface of carbon fiber bundles. The process can further apply to the subsequent applications of carbon fiber in electromagnetic wave shielding materials and metallurgical bonding at the interface of metal-based composites. In this study, the carbon fiber bundles' surface was first treated with hot nitric acid (80 °C, 30 min) to remove the polymer and activate the carbon fiber surface. Subsequently, a direct current electroplating method (3.5 V, 30 min) was used to deposit a 2 μm thick nickel film on the surface of carbon fiber bundles and carbon fiber fabric with a diameter of 7 μm. The weight of the carbon fiber increased by 1.9 times after nickel electroplating on the carbon fiber surface. To reduce the weight of the final product, efforts can be made in the future to decrease the thickness of the nickel layer. However, it is important to consider that as the nickel layer thickness decreases, the coverage of the nickel layer on the carbon fiber surface will also decrease.This research paper also provides detailed research and discussion on the relevant processes of metallization treatment on carbon fiber surfaces, including the design of electroplating fixtures, surface pre-treatment, electroplating treatment, and post-treatment.In this paper, hot nitric acid is used to replace high-temperature decomposition of polymer on the carbon fiber surface. Electroplating is employed to deposit nickel metal on the surface of carbon fiber bundles, with control over the voltage and duration of the electroplating process. The obtained nickel film thickness is observed, measured, and analyzed. Furthermore, the electromagnetic wave shielding properties of the carbon fiber with nickel electroplating are measured.