Search

The austenitic stainless steels are extensively used in industrial applications owing to their outstanding corrosion resistance. However, their use is limited in several applications due to their poor tribological properties and the need to be upgraded. This study investigates the tribological behavior of molybdenum oxide coating on AISI-316 steel deposited by low-temperature cathodic cage plasma deposition (CCPD). The wear behavior is investigated by a ball-on-disc wear tester which reveals the outstanding friction reducing capability and wear resistance of molybdenum oxide film. The film deposited by keeping on floating potential only contains the MoO3 phase, while mixed phases of MoO3 and Fe2O3 are found on the film deposited by cathodic potential. This is also supported by Raman analysis. Moreover, the successful deposition of MoO3 on floating potential reveals this system efficiency to deposit this coating on insulators. This study shows that MoO3 coating by CCPD can enhance tribological features and act as a solid lubricant coating. The CCPD system exhibits high deposition efficiency; no complicated equipment is required in this system; the deposited film is quite homogeneous, the low processing temperature is required, the rough vacuum is required, and this system compatibility with industry makes this study more effective to fulfill industrial needs.

Mechanical manufacturing processes aim to transform metallic materials into mechanical parts and components. In these processes, tools are used for cutting, punching and stamping. The ending of the useful lifetime of these tools happens with wear of its cutting edge. Such forming tools can be manufactured by several materials including AISI-M2 high-speed steel steels, and their surface properties can be modified by thermal and thermochemical treatments. In this study, an attempt is made to design and manufacture a forming tool in the laboratory without usage of computer numerical control machines. Afterwards, the manufactured forming tools are plasma nitrided at various temperatures (400–500 °C) and obtained results are compared with existing tool provided by nails manufacturing factory. The forming tools after plasma nitriding show a significant hardness improvement, increased nails production (used in civil construction), and better wear resistance as compared to the existing tool, particularly at 400 °C. The forming tool obtained in this study is easy-to-manufacture, eco-friendly plasma treatment and cost-effective, and thus it is expected that it can resolve company's technical issue regarding premature wear and tear, and rapid replacement of tool in nails manufacturing.

Ionic conductors composed of lanthanide-doped ceria with general formula DyyCe1-yO2-δ (y = 0.05, 0.1 and 0.15) were synthesized by mechanochemistry (mechanical milling), and their electrical properties analyzed to be used as solid electrolytes in low-temperature SOFC. Starting oxide reagents were milled at different times in a planetary mill and the evolution of their structures and phases with milling time and temperature (up to 1500 °C) was followed by XRD. Just milled powders were also uniaxially pressed and sintered at different temperatures (1200, 1350 and 1500 °C), and analyzed by FE-SEM, to explore their morphologies as a function of temperature and Dy content. The electrical properties of these materials and undoped commercial CeO2 were analyzed by impedance spectroscopy at different temperatures (200–650 °C) and frequencies (100 Hz - 1 MHz). Results showed that mechanochemistry is a suitable method to obtain the DyyCe1-yO2-δ systems after 20 h of milling, since XRD patterns of these milled powders reveal the formation of fluorite-type cubic solid solutions for all studied compositions. Increasing of temperature generates a higher crystallinity in these materials while the absence of phase transitions in them is corroborated at 1200 °C. Analysis of electrical properties of samples sintered a 1200 °C corroborates the viability of these systems to be used as solid electrolytes in the SOFC technology, being that high dc conductivities (σdc) were obtained for all doped samples, especially for the composition Dy0.1Ce0·9O2-δ, which showed a σdc = 1 × 10−1.91 S cm−1 at 650 °C. This value represents an increase of almost three orders of magnitude for this composition with respect to the undoped CeO2 sample (y = 0, σdc = 1 × 10 −4.83 Scm−1).

Here, pulsed plasma nitriding of AISI-316L austenite stainless steel is conducted in a narrow range of temperature 510-550 °C and simultaneous combination of expanded austenite phase, and homogenous, dense chromium nitride phase is attained in a single processing unit, with relative low-cost equipment and single-step processing. The results show a noteworthy enhancement in nanohardness at 530 °C, whereas best wear resistance is achieved by processing at 550 °C. A dual-layer structure is obtained constituted of expanded austenite phase covered by quite homogenous chromium nitride phase, which is probably responsible for the dramatic surface improvement. The wear mechanism is changed after plasma processing (abrasive to adhesive wear), and the friction coefficient is reduced and smoother, particularly for the sample treated at 530 °C. Interestingly, the corrosion resistance is also found to be enhanced, even in the presence of chromium nitride (which usually deteriorate the corrosion resistance), which is probably credited to the formation of fine-grained and homogeneous CrN layer over the expanded austenite phase. This study suggests that the development of homogenous CrN layer over the expanded austenite structure is highly valuable for mechanical and tribological features, and it enhances the corrosion resistance.

Plasma nitrocarburizing is a thermochemical diffusion process with simultaneous diffusion of nitrogen and carbon on the surface of metals at elevated temperatures. In this work, the influence of methane (carbon-containing precursor) concentration on the surface properties of the nitrocarburized AISI-304 in the presence of a cathodic cage is studied. The samples are treated at fixed conditions (400 °C, 3 h, 150 Pa), while 0–10% methane is admixed in nitrogen–hydrogen mixture discharge. The addition of methane results in a gradual decrease in the surface hardness with indentation depth of sample compared to the plasma nitriding, which indicates an improved load-bearing capacity. The XRD pattern shows the abrupt phase transformation from austenite (fcc) to the martensite (bcc) phase for a small methane concentration and simultaneous carbon and nitrogen expanded austenite phases for higher methane fraction. The thickness of both N-enriched and C-enriched layers increases up to 4% of methane addition, and then the thickness of the N-enriched layer decreases. The corrosion rate also showed a non-monotonic response to the methane fraction.

This research aimed to obtain a C-based coating electrochemically applied on an AA6063 alloy. Two electrochemical cells were designed and manufactured to obtain the C-based coating film on flat and cylindrical samples. Structural and microstructural characterizations were performed along with fatigue and corrosion performance testing. The structural and microstructural characterization revealed that the C-based coating deposited on AA6063 corresponded to carbon nanofibers and/or polycrystalline graphite. The performance testing showed an increase in fatigue life along with a decrease in corrosion resistance. The fracture surfaces of the fatigued samples were inspected by Scanning Electron Microscopy and 3D optical microscopy to correlate them with fatigue life estimation. The aforementioned process is a step towards the future development of a complete coating system that will overcome corrosion susceptibility. The carbon film obtained by this electrochemical route has not previously been reported elsewhere.

Pulsed plasma nitriding and post-oxidizing process have been applied to hot work H13 tool steel to enhance the tribological properties (friction coefficient and wear rate). Nitriding was accomplished under specific conditions to generate a free white layer surface in order to avoid an abrasive wear mechanism. Post-oxidizing treatment was carried out in the same reactor after finishing the nitriding treatment; processing time was varied for 30 and 60 min. The morphology, phase’s composition and wear performance of duplex-treated samples were evaluated by scanning electron microscopy, x-ray diffraction analysis and pin-on-ball wear technique. The results show that the duplex treatment produces a bilayer arrangement constituted by an 80 μm diffusion zone with expanded martensite as the main phase underneath a 2–4 μm hematite–magnetite-oxidized layer. The duplex treatment modified the main wear mechanism of the nitrided sample from abrasive to plastic yielding. The changes in wear mechanisms resulted in a noticeable decrease, about 40%, in friction coefficient for oxidized samples in comparison with the nitrided-only sample. It was also established that the lowest friction coefficient values can be obtained when hematite is the main phase in the oxidized layer.

The present research deals with the comparative wear behavior of a mechanically milled Al-6061 alloy and the same alloy reinforced with 5 wt.% of Al2O3 nanoparticles (Al-6061-Al2O3) under different dry sliding conditions. For this purpose, an aluminum-silicon-based material was synthesized by high-energy mechanical alloying, cold consolidated, and sintered under pressureless and vacuum conditions. The mechanical behavior was evaluated by sliding wear and microhardness tests. The structural characterization was carried out by X-ray diffraction and scanning electron microscopy. Results showed a clear wear resistance improvement in the aluminum matrix composite (Al-6061-Al2O3) in comparison with the Al-6061 alloy since nanoparticles act as a third hard body against wear. This behavior is attributed to the significant increment in hardness on the reinforced material, whose strengthening mechanisms mainly lie in a nanometric size and homogeneous dispersion of particles offering an effective load transfer from the matrix to the reinforcement. Discussion of the wear performance was in terms of a protective thin film oxide formation, where protective behavior decreases as a function of the sliding speed.

Zinc-oxide (ZnO), a solid lubricant coating, can increase the wear resistance of steels by working as a self-lubricant. In this study, ZnO film is synthesized using the cathodic cage plasma deposition (CCPD) technique, using galvanized steel cathodic cage (steel cage with zinc coating). The effect of gas composition (H2 is added in Ar-O2) is investigated to optimize the film properties. The surface hardness is increased more than twice in each processing condition. The deposited film shows ZnO phases for samples treated with low hydrogen contents and a combination of ZnO and magnetite phase (Fe3O4) with higher hydrogen contents. The thickness of film reduced from 1.28 μm to 0.5 μm by increasing the hydrogen composition. The wear resistance is expressively increased by film deposition, and the abrasive wear mechanism is changed to an adhesive wear mechanism. A significant decrease in wear rate is observed, specifically by increasing the hydrogen contents. The friction coefficient as a function of sliding distance is smoother and lower than the base material in each condition. This study suggests that the CCPD technique can effectively deposit the solid lubricant coating of ZnO, and it can be used to enhance the tribological properties of steel samples. Moreover, this technique is convenient due to its better deposition efficiency, eco-friendly (no chemicals are involved), simple and relatively low-cost equipment, and low processing temperature. Thus, it can be advantageous for industrial sectors interested in materials with exceptional tribological properties.

The longevity of metal-on-polyethylene (MoP) joint replacements, in which a polished CoCr component articulates with a polyethylene liner, may be restricted by mechanical instability or inflammation resulting from osteolysis caused by polyethylene wear debris. Recently, laser surface texturing (LST) has emerged as an effective method to improve the tribological performance of lubricated friction pairs. The present work reports a microstructural and tribological study of surface microtextured CoCr alloy discs, modified by the LST method using a pulsed Nd:YAG laser, tested against Ultra High Molecular Weight Polyethylene (UHMWPE) cylindrical pins. Four different texturing patterns varying laser parameters such as peak power, pulse width, repetition rate and travel speed were investigated. An untextured set of CoCr alloy discs was used as reference. The microstructure and mechanical properties of the microtextured CoCr alloy discs were investigated by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, atomic force microscopy, profilometry and nanoindentation test. The coefficient of friction and wear of the UHMWPE pins were determined by means of a pin-on-disc tribometer under lubricated sliding conditions. The microstructural analysis on the laser microtextured CoCr alloy revealed a grain refinement of secondary phases with absence of typical carbides resulting in an increased nanohardness. In addition, all texturing patterns on the CoCr alloy discs promoted a reduction on the coefficient of friction, compared against untextured CoCr alloy discs. Furthermore, it was found that UHMWPE wear was reduced when articulating against dimple textured CoCr alloy discs.

Mixtures of Ni-based filler metal without and with 0.5, 1, and 2% WC nanoparticles (NPs) were methodologically tested in order to improve the wear behaviour of WC/Ni-based overlays deposited on low carbon steel by the plasma transferred arc (PTA) process. On adding 2% WC NPs, the longitudinal direction overlay microstructure was modified to have a fibrous appearance. The mechanism to improve WC particle distribution and thus prevent microcrack propagation in the overlays implies a liquid-phase viscosity change. Results of pin-on-disk tests in the overlay using filler metal with 2% WC NPs show that the combined effect of fibrous microstructure and W-rich phases in the overlay, decreases the volume loss by 76% and 78% in comparison with overlays without WC NPs for a 1 and 5 N load, respectively. These outcomes might be of interest for the mining industry, where machinery and equipment are exposed to extreme wear conditions.

In the present study, the properties of thin coatings deposited on biocompatible 316L steel to improve the wear resistance were investigated. A thin Ti nanolayer of thickness 400 nm was deposited by thermal evaporation (sputtering), and the Ti-coated steel was subjected to plasma oxidation treatment for different times. All the samples were characterized using metallographic techniques, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), and roughness and nanohardness tests. A pin-on-disc tribometer was used to evaluate the wear resistance of the coatings under lubricated sliding condition. The results showed that the TiO 2 film is formed as a function of thermal oxidation time. The coating had a beneficial effect on the wear resistance depending on the roughness. Other coating characteristics such as topology of surface modified by TiO 2 diffusion and nanohardness were assessed.

This study aims to synthesize a molybdenum oxide coating through cathodic cage plasma deposition (CCPD), employing a molybdenum cathodic cage and evaluating both cathodic and floating potentials treatment. Structural, morphological, and wear properties of coated AISI 316 samples are investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, Rockwell-C adhesion test, and ball-on-disc wear tester. Cathodic potential treatment results in a coating containing agglomerated nanostructures (spherical nanoparticles) composed by molybdenum oxide (MoO3), iron-oxide (Fe2O3), Fe2Mo3 and Fe3Mo phases. The coating generated by floating potential mainly contains molybdenum oxide (MoO3) phase and shows homogeneously dispersed microplatelets with quite a regular shape. The Rockwell-C adhesion test showed that the layers on both samples exhibit good adhesion strength with the substrate. The samples treated at floating potential reveal better wear resistance and lowest/smooth friction coefficient. This shows that molybdenum oxide coating by CCPD using floating potential can be used as a solid lubricant in tribological applications.

In order to improve the tribological behavior of austenitic stainless steel, a novel composite coating based on reduced graphene oxide-Ni (rGO-Ni) is presented. These coatings were prepared by sol–gel using a mixture of Ni-rich xerogel films and reduced graphene oxide (rGO), with a heat treatment at 1000 °C for 1 h under an Ar flow. Raman spectroscopy confirmed that the rGO-Ni coating was formed. The rGO-Ni coating demonstrated an unusual surface topography, combined with multiple lamellar carbon growth and refined grains characterized by automatic crystal orientation mapping as determined through electron backscattered diffraction (EBSD). The rGO-Ni-composite coating exhibited a high elastic behavior from a multi-step nanoindentation with a depth of 900 nm and wear loss of ~ 0.05 to 0.3 mm3 at 1 to 5 N. It was found that the increase on wear resistance was due to both the self-lubrication properties of the rGO and the harness of refined grains on the coating.

AISI D2 tool steels are widely applicable in dies or tools manufacturing. Unfortunately, their use is drastically reduced due to short lifetime. Plasma nitriding without formation of white layer is an effective technique to improve the lifetime of tool steel by improving tribological features. Usually, white layer formation is unavoidable, thus its detrimental effects (its brittle nature causes severe abrasive wear) must be removed or reduced by some alternative treatment. Here, in this study, we attempted to investigate the effect of post-oxidation of nitrided tool steel with and without presence of white layer on its wear performance and its dynamic mechanical response. The micro-hardness and nano-hardness are enhanced by plasma nitriding, but a slight decrease with post-oxidation treatment. The post-oxidized samples show the formation of hematite and magnetite phases, which changes the wear mechanism of nitrided samples from abrasive to adhesive wear. This study suggests that the removal or avoidance of white layer formation is not compulsory, and its unfavorable effects on tribological performance of tool steel can be escaped by post-oxidation for a short time of 1 h. Analysis of contact stiffness and storage and loss moduli shows that the post-oxidation can result in surfaces less prone to cracking under cyclic loads. Duplex treatment by combining plasma nitriding and plasma oxidation is carried out in the same processing reactor by changing processing gasses admixture, thus it is favorable and economical for large scale industrial applications.

The aim of this work is to improve the surface properties of aluminum, using active screen plasma nitriding (ASPN) equipped with aluminum active screen (Al-AS). The samples are treated in fixed processing conditions, except 0–50% hydrogen is admixed in nitrogen gas, for the better removal of the native oxide layer. The samples are analyzed using the micro-hardness tester, X-ray diffraction, scanning electron microscope and dry ball-on-disc wear tester. The results show that using Al-AS (particularly at 40% hydrogen), excellent film quality with better uniformity, surface hardness and wear resistance can be attained with aluminum nitride (AlN) as a leading phase. Using Al-AS, the deposition of inappropriate material (such as iron in some reports) can be avoided with improved results even in short processing time (3[Formula: see text]h).

The influences of discharge current density and oxidation process duration on surface morphology, crystalline phase composition, and electrochemical corrosion performance of pulsed plasma-oxidized AISI 316L stainless steel were studied. Analysis of results shows that samples treated through DC pulsed plasma oxidation (0.5 mA/cm2, 60 min) exhibit corrosion current values of 2.0 × 10−4 mA/cm2 which represent one eighth of the corrosion current obtained for untreated samples and one half that of chemically passivated samples. Scanning electron microscopy, grazing incidence x-ray diffraction, and Raman analysis show that the improved corrosion performance of oxidized samples could be attributed to morphological changes of the oxidized layer which is composed of hematite and magnetite iron oxides. Corrosion performances of DC plasma-oxidized samples suggest that through this technique, it is possible to obtain comparable or even better corrosion performance than techniques, such as inductively coupled plasma-oxidizing process, but without the inherent higher instrumental requirements of radiofrequency plasma processes.

In this work, plasma-nitrided AISI 316L stainless steel samples were performed by ion nitriding process under pulsed direct current (DC) discharge at different current densities (1 to 2.5 mA/ cm 2 ). The effect of nitriding current density on the size of crystalline coherently diffracting domains (crystallite size) and strain grade was investigated using X-ray diffraction (XRD) coupled with Williamson-Hall method. Additionally, hardness and wear resistance of the nitriding layer were characterized using a Vickers indenter and pin-on-disk technique respectively. Results showed a decrease in crystallite size from 99 nm for untreated samples to 1.4 nm for samples nitrided at 2.5 mA/cm2 promoted both: an increase in hardness from 226 HV25g to 1245 HV25g, and a considerably decrease in volume loss by wear effect.

The influence of pulse time (tp) variation on hardness, crystalline phases and electrochemical corrosion susceptibility of plasma nitriding 316L was investigated. Hardness test, X-ray diffraction, scanning electron microscopy and electrochemical polarisation tests let to identify the best processing conditions. Nitriding at t p = 5 ms in a 100 Hz discharge increased the 316L hardness around four times and decreased its corrosion susceptibility one order of magnitude. The X-ray diffraction analysis showed the shifted reflections for the expanded austenite and let to identify an anisotropic strain with expansion lattice around 7·5 and 9% for (111) and (200) orientations respectively. For the evaluated t p range, the increase in the pulse length has not beneficial influence on surface hardness; on the contrary, there is a decrease in its value when t p grew from 5 to 8 ms. Corrosion and hardness performance has been related to the strain level and to the nitrogen content.

In this paper, we present the results of a duplex plasma nitriding followed by an oxidizing stage process (which is also referred as oxy-nitriding) on the corrosion behavior of a 17-4PH precipitation hardening stainless steel. The formation of both, expanded martensite (b.c.t. α′N-phase) and chromium oxide (type Cr2O3) in the subsurface of oxy-nitrided samples at specific controlled conditions, leads in a noticeable increasing in the time-to-rupture during the sulfide stress cracking test, in comparison with an untreated reference sample. Oxy-nitriding improves the corrosion performance of the alloy when it is immersed in solutions saturated by sour gas, which extends the application potential of this type of steel in the oil and gas extraction and processing industry. The presence of the oxy-nitrided layer inhibits the corrosion process that occurs in the near-surface region, where hydrogen is liberated after the formation of iron sulfides, which finally produces a fragile fracture by micro-crack propagation; the obtained results suggest that oxy-nitriding slows this process, thus delaying the rupture of the specimen. Moreover, oxy-nitriding produces a hard, sour gas-resistant surface, but do not significantly affect the original chloride ion solution resistance of the material.

The nonalloyed steels are very cost-effective, but their usefulness in numerous applications is imbedded due to low mechanical strength. The strength of several steels can be improved by nitriding; however, nonalloyed steels are not suitable. They can be nitrided by introducing special nitriding alloys (like chromium, aluminum, etc.) during manufacturing or some interlayer deposition, but it is quite expensive. The aim of this study is to improve nitriding capability of nonalloyed steels without any additional treatment. This is done by using alloyed stainless steel active screen in active screen plasma treatment, which provides an adequate amount of chromium to form stable and hard nitrides. The processed samples are characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, pin-on-disc wear tester, hardness tester and potentiodynamic polarization test.

In this work, the effect of nitriding current density on hardness, crystalline phase composition, layer thickness and corrosion rate of AISI 4340 steel has been studied. X-ray diffraction analysis shows that thin layers formed during nitriding process are constituted of γ-Fe4N for samples processed between 1 and 2.5 mA/cm2. Thickness of nitrided layer increases proportionally to current density (0 μm for 0.5 mA/cm2 to 15 μm for 2.5 mA/cm2). Plasma nitriding increased the surface hardness from 300 HV50g for untreated sample, to around 800HV50g for nitrided samples at 1 mA/cm2. While the untreated samples exhibited a corrosion rate of 0.153 mm per year, the corrosion performance was improved up to 0.03 mm per year at current densities above 1 mA/cm2, which is about one fifth of the corrosion rate of the untreated sample.

The effect of current density and gas mixture on surface properties of low alloy steel processed in a pulsed plasma nitriding system under strictly controlled conditions is evaluated in this work. As current density is a parameter that has not been particularly studied, this study seeks to demonstrate that current density and gas mixture have an important influence on the process and an adequate combination of these two variables is essential to obtain the desired surface properties: hardness, white layer thickness (or absence), and crystalline phases of the modified layer. In this sense, samples processed at low current densities with low nitrogen content in the plasma atmosphere show a diffusive nitrides region which increases the hardness from 250 HV (untreated reference sample) to 400 HV without the presence of the typical white layer that is sometimes undesired due to its fragility and tendency to break. On the other hand, treatment at high current densities and high nitrogen concentrations leads to obtain pieces with a homogeneous single-phase layer (γ-Fe4N) with an outstanding corrosion performance, diminishing the corrosion rate from 0.160 μm per year in the untreated sample up to 0.050 μm per year.

Austenitic stainless steels are of prime importance in many industrial sectors because of their excellent corrosion resistance; however, their poor mechanical and tribological features lead to their reduced applicability. In this regard, low-temperature cathodic cage plasma nitriding (CCPN) can be used to improve surface properties of steels without scarifying the inherent corrosion resistance. In this study, AISI-316 samples are processed in CCPN reactor at a temperature of 400 °C, for the treatment time of 4 h, at a pressure of 150 Pa and variable pulsed duty cycle (15–75%). The microstructure and mechanical features are analyzed using x-ray diffraction, scanning electron microscopy, microhardness tester and ball-on-disc wear tester. The anodic polarization test in 3.5% NaCl is conducted to examine the corrosion properties. The results show that hardness is enhanced up to 1327 HV at low duty cycle, which is considerably higher than base material (278 HV). The wear rate is found to be reduced up to 90% over base material by processing at low duty cycle. The base material exhibits severe abrasive wear, and the nitrided sample has dominant adhesive wear. The corrosion rate is found to be reduced up to 95% over base material for the sample nitrided at low duty cycle. This study shows that wear and corrosion resistance in CCPN can be significantly boosted by reducing the pulsed duty cycle.