TiO2-ZrO2 composite coating was fabricated on TC4 titanium alloy via plasma electrolytic oxidation (PEO) in an alkaline electrolyte composed of Na2SiO3 and KOH. The effect of the content of K2ZrF6 as an electrolyte additive on the microstructure, elemental composition, phase structure, thickness, hardness, adhesion and corrosion resistance of PEO coating was investigated. The results show that the addition of K2ZrF6 contributed to the enhancement of coating thickness (from 4.04 ± 0.62 μm to 11.44 ± 0.35 μm) and hardness (488.4 HV to 779.8 HV). As the K2ZrF6 concentration increased, both the quantity and diameter of micropores on the surface of the PEO coatings decreased firstly and then increased. The minimum porosity and pore size were obtained in the electrolyte containing 6 g/L K2ZrF6. The coatings were mainly composed of Ti, anatase TiO2 and rutile TiO2. EDS test proved that K2ZrF6 successfully participated in the PEO reaction. The composite coating prepared in silicate electrolyte system with 6 g/L K2ZrF6 exhibited the highest corrosion resistance. Furthermore, the formation mechanism of the ZrO2-TiO2 composite coating was discussed in detail.

This study investigates the microstructure, the mechanical properties, the topography and the tribological behavior of a composite coating obtained by cold spray, as a potential candidate for its use in internal combustion engines in the automotive sector. The coating consists of a 410 L matrix and M2 tool steel reinforcements. For comparison, a single component 410 L cold sprayed coating and a wire arc coating, used in some of today's car engines, are also studied. Post-spraying, the coatings underwent specific surface finishing. Their microstructure and topographies were observed. A lubricated reciprocating sliding test was performed, resulting in an exceptionally low friction coefficient and negligible wear, even in harsh conditions for the composite coating. The analyses revealed that the surface finish creates protuberances due to the presence of hard M2 particles, activating a series of mechanisms bringing to the stabilization of a tribofilm. This can be considered responsible for the exceptional tribological properties observed. This study proposes the application of surface textures with protuberances, in particular, their use in lubricated contacts in presence of fully formulated oils, and how cold spray is a suitable process to easily produce them.

The inherent brittleness of amorphous alloys limits their tribological properties. Ultrasonic impact treatment (UIT), applied without preloading, has been used to improve the tribological performance of Ti-based amorphous alloys. Following UIT, the impacted surface softened, whereas the sample cross-section hardened. The change in hardness could be controlled by varying the UIT duration and ultrasonic power. UIT leads to an increase in relaxation enthalpy, suggesting higher free volume and enhanced plasticity. This improved plasticity is evidenced by the Vickers indentation morphologies and the pop-in phenomena of the nanoindentation curves. Regardless of whether the tribology testing was performed in air or in a 3.5 % NaCl solution, UIT led to noticeable reductions in both the coefficient of friction (COF) and the wear rate. The corrosion resistance improved noticeably in both static and sliding states. The primary wear mechanisms were adhesion, abrasion, and delamination. Compared to sliding in air, the COF and wear rate were lower in the NaCl solution. Post UIT, the higher free volume facilitates oxidation in air and the formation of protective corrosion products in the NaCl solution, which is beneficial in reducing adhesion. Simultaneously, the improved plasticity of UIT may contribute to resistance to fatigue and delamination. Therefore, UIT is a simple and feasible method for significantly improving the tribological performance of amorphous alloys.

In this paper, the blue ceramic coating was prepared in situ on the surface of AZ31 magnesium alloy using Ti and Al composite salt as electrolyte by PEO technology. The results show that the light wave response range of the prepared ceramic coating is all in 430–470 nm with different n(Ti)/n(Al) atomic percentage in the electrolyte, but the blue color saturation of the ceramic coating increases with the increase of n(Ti)/n(Al) ratio. XRD and XPS analysis show that Ti exists in the form of Ti4+ and Ti3+, Al exists in the form of Al2O3, and a small amount of Ti3+ ions occupy the Al3+ lattice in the form of replacement solution, forming (Al2-xTix)O3 solid solution. This is the chromogenic mechanism of PEO-MgO ceramic coating changing from off-white to blue. Finally, due to the PEO plasma discharge generated on the surface of magnesium matrix in the micron level spot melting pool, the formation of the blue material of Al2O3 doped with Ti and the oxidation and sintering of magnesium matrix at high temperature synchronously, thus achieving in situ color ceramic treatment on the surface of magnesium alloy with low melting point.

The growth of α-Al2O3 layer on ODS FeCrAl alloys NF12 (Fe-12Cr-6Al-0.5Ti-0.4Y-0.4Zr-0.25Ex.O) and SP10 (Fe-15Cr-7Al-0.5Ti-0.4Y-0.4Zr-0.24Ex.O) was investigated by means of the oxidation tests under air atmosphere at 1273 K up to 10 h. The inward oxygen diffusion was promoted through the oxides of reactive elements (i.e., Ti, Y and Zr) formed along the grain boundaries of α-Al2O3 layer, and the inward growth of the layer was accelerated. The shearing stress required for the layer exfoliation was quantitatively evaluated by micro-scratch tests. The adhesion of α-Al2O3 layer formed on the ODS alloys was reinforced by so-called anchoring and pegging effects.

This study explores using high-energy pulsed laser to improve the surface property and corrosion behavior of Ti-6Al-4V, aiming to develop a more eco-friendly and efficient approach. The study comprises conventional cast samples, advanced 3D-printed samples, and their respective laser-treated counterparts, all tested in a 3.5 wt% NaCl solution. The findings showed that sample 3 (as-3D-printed) had a more stable passivation film than sample 1 (as-cast). The laser-treated surface of sample 2 (laser-treated cast) greatly enhances film stability and resistance. Moreover, sample 4 (laser-treated 3D-printed) exhibited significantly better corrosion performance compared to sample 3 (as-3D-printed) due to the increased thickness of the passivation film in the laser-treated samples, resulting in higher film corrosion resistance. The results reveal that laser remelting treatment can eliminate macroscopic defects, reduce grain size, increase grain boundary density, and generate denser and more stable passivation films on the surface of Ti-6Al-4V, leading to reduced corrosion currents during dynamic potential polarization. Furthermore, laser remelting treatment has the capability to transform and refine the α phase into a finer lamellar and needle-like structure, thereby increasing the density of passivation nucleation sites during the corrosion process, resulting in the formation of a high-density passivation layer, and ultimately improving the corrosion resistance. By gaining a better understanding of the underlying mechanisms involved in high-energy pulsed treatment, this work provides valuable insights that can be used to optimize the treatment process and improve the overall surface properties of Ti-6Al-4V alloys.

Cobalt–chromium–molybdenum (CoCrMo) alloy is frequently utilized to replace artificial joints and dental components. Tantalum (Ta) coating is used to improve the osteogenic property of CoCrMo alloy. Annealing treatment can increase the Ta coating adhesion and further improve wear resistance and biocompatibility. In this study, two kinds of thicknesses of Ta coatings were applied on CoCrMo alloy substrates via magnetron sputtering technology. The average thicknesses of the Ta coatings were 4.3 and 9.5 μm. The Ta coatings were annealed for 5 h at 800 °C, 900 °C, and 1000 °C, respectively. Results indicated that heat treatment improved the adhesion of the coatings. The Ta coatings were composed of stable body-centered cubic phase (α-Ta) and metastable tetragonal phase (β-Ta). The Ta coating with a thickness of 4.3 μm exhibited excellent wear resistance after being annealed at 800 °C, with little variability in the friction curve and a low average coefficient of friction. The adhesive force of the two coated samples increased initially and subsequently dropped as the annealing temperature increased. At 900 °C, the Ta-coated samples exhibited the highest adhesive force; after being annealed, the rate of cell proliferation increased. At 900 °C, samples with Ta coatings exhibited the highest rate of cell multiplication and the best cell compatibility compared with the other samples. Ta coatings' adhesive force, wear resistance, corrosion resistance, and cytocompatibility were all significantly enhanced at various annealing temperatures. Thus, the results of this work are a useful benchmark for the surface modification of metal implants used in medical procedures, and Ta coatings are a practical orthopedic material for the replacement of joints and bones.

Diamond-like carbon (DLC) films were grown using a superimposed high-power pulse magnetron sputtering and direct current magnetron sputtering (HiPIMS-DCMS) deposition system at various bias voltages from 0 to −350 V. The microstructure, mechanical and tribological properties of the films were studied in relation to bias voltage. The results suggested that the deposition rate of DLC films decreased gradually with the enhancement of bias voltages. The surface roughness of DLC films decreased from 2.81 nm to 0.54 nm. The values of ID/IG of DLC films decreased first and increased later with the enhancement of bias voltages, and the value of ID/IG was the minimum at −150 V. Therefore, the highest sp3 CC fraction of DLC film was obtained when deposited at −150 V. Moreover, the hardness and internal stress of DLC films also show the law of increasing first and decreasing later. DLC film obtained the maximum hardness and highest internal stress of 32.0 GPa and − 2.08 GPa at −150 V. Finally, the friction test suggested that the films had excellent tribological performance. In particular, the film deposited at −150 V had excellent tribological properties, including low friction coefficient (0.095) and low wear rate (1.36 × 10−7 mm3/N·m).

The rapid development of nanoscale surface modification technology has led to the development of superhydrophilic, superhydrophobic, and slippery liquid-infused porous surfaces (SLIPS) in recent decades. These surfaces have excellent self-cleaning and anti-contamination performance, and many studies have reported their industrial applications. Industrial and modern medical applications of titanium are rapidly expanding owing to its advantages of chemical stability, high mechanical strength, stable corrosion resistance, and biocompatibility; however, performing surface modification of titanium remains challenging. In this study, superhydrophilic, superhydrophobic, and SLIPS were fabricated on titanium using a simple surface fabrication method, and their wettabilities were analyzed and compared. Furthermore, we succeeded in applying the method used in this study to bulky and complex objects. Chemical and physical analyses were performed to confirm the fabrication, wettability properties, and nanostructures of the modified surfaces. The simple fabrication method presented a significant advancement as there are no limitations in its application to large areas, complex shapes, or mass production, unlike existing titanium wettability modification methods.

Nowadays, copper-titanium coatings have invited extensive attention from researchers in the surface modification of industrial and biomedical materials due to their excellent mechanical properties and biocompatibility. The electrospark deposition technique was used for CuTi coatings deposition on the Ti6Al4V alloy by processing in a mixture of copper and titanium granules at a copper concentration from 10 to 90 at.%. For the first time, electrospark CuTi coatings with a wide range of copper and titanium ratios are obtained on Ti6Al4V titanium alloy. It is revealed that both cathode mass gain and coatings thickness rise with the copper concentration increase in the mixture of granules. According to EDS analysis, the copper concentration in the coating linearly grew with a growth of its content in the mixture of granules. According to the data of X-ray analysis, intermetallic compounds were found in the structure of the coatings: CuTi3, CuTi, Cu4Ti3, and Cu3Ti. Detected phases provide the coating microhardness up to 6.7 GPa. Polarization tests in 3.5 % NaCl solution showed corrosion resistance growth with a copper content decrease in CuTi coatings. The oxidation resistance at a temperature of 900 °C grows with an increasing copper concentration in the coating structure. Cu-enriched sublayer is formed on upper layers of Ti6Al4V alloy after CuTi coating oxidation at 900 °C. The wear rate of the coated samples as a function of copper concentration had the form of a parabola, with a minimum for the coating made in an equimolar mixture of copper and titanium. The use of electrospark CuTi coatings makes it possible to increase the wear resistance of the Ti6Al4V alloy surface up to 11 times.

During the laser cladding process, the mass, energy and momentum inputs of the powder flow play a significant role in the evolution of the molten pool and microstructure. Considering the mass, energy and momentum inputs of the powder flow can significantly improve the accuracy of the simulation. In this study, an integrated modeling framework containing a computational fluid dynamics (CFD) model with the powder source described by ray tracing method and a cellular automata (CA) model was established to investigate the effects of powder flow on the evolution of the molten pool and microstructure during the laser cladding process. The accuracy of the modeling framework was verified by experiments with different powder particles velocities. The results indicated that the powder flow impact changed the vortices of the molten pool, resulting in less high–temperature molten metal flowing into the tail but more high–temperature metal accumulating at the bottom of the molten pool, thus decreasing the height but increasing the depth of the cladding layer. And the tail of the molten pool is more easily to be nucleated than other zones for the same reason. Increasing the powder particles velocity increases the percentage of equiaxed grains in the cladding layer from 46.21 % to 52.64 % and the aspect ratio of the grains at the top of the cladding layer decreases by 16.92 %. This study helps to optimize the laser cladding process and provides a basis for regulating the microstructure by controlling powder flow.

Herein, we propose a method for producing WC composite ceramic coatings on tungsten alloy surfaces using directed energy deposition (DED). Different microstructures of DED single tracks were obtained with different line energy densities. Two parts of DED tracks were discovered, which contained the WC fusion zone and the WC-Ni-Co melting injection zone. The WC fusion zone mainly comprised four typical phases, WC, W2C, W, and C(diamond, graphite (D, G)), which were present in the microstructures of the tracks in different combinations. The key factor for determining the microstructure evolution was C content. With higher line energy density, more tungsten alloy melted, which decreased C content in the melt pool. As C content decreased, the composition of the microstructure transformed to C(D, G) + WC + W2C → WC + W2C → W2C + W + a small amount of γ-(Ni, Co). C content gradually decreased from the top to the bottom of the melt pool, resulting in a gradient microstructure transition. The microstructure and property could be tuned by controlling the C content. The hardness was the highest, 2300 HV, at 40.7 at.% C with WC-W2C eutectoid. This study provides practical insights for producing coatings on tungsten alloy surfaces with optimized process parameters and for tailoring mechanical properties.

This study focused on the synthesis of Niobium/Hexagonal-Diamond/amorphous-carbon (Nb/H-D: a-C) films on AISI-321 alloy. The substrate heating used as a vital deposition parameter to tailor structure of the films in an unbalanced magnetron (UB-M) sputtering system for the first time. The substrate heater temperature (Th) ranged between (RT) to 150 °C. The results indicated that increasing the substrate heater temperature promoted the abundance of H-Diamond crystals through the solid phase separation. Therefore, the film deposited at the highest temperature (150 °C) demonstrated the highest plenty of H-Diamond. Electrochemical impedance spectroscopy (EIS) measurements (after 2, 8, 24, 72, and 168 h immersion) and polarization tests (after 168 h immersion) disclosed that increasing the substrate heater temperature positively affects the corrosion resistance of (Nb/H-D: a-C) films. The results proved that the film deposited at the highest temperature of 150 °C, demonstrated the exceptional corrosion protection efficiency of 99.69 %. Moreover, this film presented acceptable low-frequency impedance (|Z|10KHz) and total resistance (Rt) values of >108 Ω·cm2 and >117 MΩ·cm2 at all immersion times in 3.5 wt% NaCl solution. The highest abundance of the H-Diamond phase, with remarkable chemical inertness at higher substrate heater temperatures, can be an effective reason for elevating anti-corrosion performance of the films. Additionally, as the substrate heater temperature enhanced from RT to 150 °C, mechanical properties illustrated an remarkable increment trend (increasing hardness from 20 GPa to 32.7 GPa and the elasticity modulus from 407 GPa to 470 GPa). Moreover, the anti-wear performances of the films significantly improved with increasing substrate heater temperature, reducing the wear rate from 9.4 × 10−6 to 9 × 10−7 mm3/N·m. These results are mainly attributed to the highest abundance of the superhard H-Diamond phase in the film deposited at higher substrate heater temperature. In conclusion, the (Nb/H-D: a-C) film synthesized at 150 °C represented a promising candidate for tailoring the electrochemical and anti-wear performances of AISI-321 alloy.

Ti-Al2O3 composites have demonstrated favorable characteristics for use in load-bearing biomedical implant applications; however, the influence of Al2O3 reinforcement particles and Ti-Al intermetallics on the electrochemical and tribo-electrochemical responses of Ti are not well-understood. This study explored the corrosion and tribocorrosion characteristics of powder metallurgy-manufactured Ti-Al2O3 composites in a simple physiological saline solution at body temperature. Electrochemical analysis was performed by electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization and tribo-electrochemical mechanisms were explored under open circuit potential (OCP) against a 10 mm diameter alumina ball in a ball-on-plate tribometer with reciprocating configuration. Results revealed that the corrosion behavior of Ti was adversely affected by the development of a heterogeneous oxide film on the Ti matrix and the Ti-Al intermetallic phases formed by the interaction of Ti and Al2O3 particles. However, there was a drastic improvement in tribocorrosion behavior, evidenced by decreased corrosion tendency under sliding and a marked reduction in wear volume, primarily as a result of the decreased wear damage resulting from the load-bearing reinforcements.

Titanium monoxide (TiO) is golden in color, and of good chemical inertness and high hardness, making it a potential candidate for decorative and protective coatings. In this study, a TiO layer was coated on Ti alloy substrate through a combination of cathode plasma electrolysis (CPE) and comproportionation between the Ti substrate and Ti4+ from the electrolyte. The thickness of the obtained TiO layer was around 500 nm, with a hardness of 11 GPa, a modulus of 220 GPa and a critical load of 55 N. The coefficient of friction of the CPE-treated sample vs. ZrO2 ball was decreased from 0.4 to 0.6 to around 0.2 when the Hertz pressure was less than 885 MPa. The wear rate of the CPE-treated sample was reduced by ~450 times compared with that of the untreated Ti alloy. Correspondingly, the wear rate of the ZrO2 ball was reduced by ~170 times. In addition, wear resistance of the CPE-treated samples was also significantly improved for common metallic materials (such as stainless steel, carbon steel, or copper alloy) as the counterpart. The surface morphology evolution and the mechanical properties of the TiO layer can avoid the severe abrasive wear as well as adhesive wear, and contribute to the excellent antiwear effects. CPE demonstrates a technologically relevant capability, especially in forming a TiO antiwear layer on Ti alloy.

This study investigates the development of surfaces that combine wear-resistance and solid lubrication properties using single low-temperature plasma carburizing treatments associated with the metal dusting phenomenon. The surfaces consisted of a regular cementite (Fe3C) layer and a film composed by vertically aligned carbon nanotubes (VACNT) grown over the carburized layer. For that, specimens of AISI 1005 steel were used as a substrate. A fractional factorial design of experiments was conducted to identify the best processing conditions to achieve the required Fe3C-VACNT surfaces. Morphological and structural aspects of the surfaces were assessed by scanning and transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The results show that the carburizing performed between 600 and 700 °C and with plasma power densities ≥0.30 W/cm2 were effective for developing the bilayer surfaces. A signature of that process was a temporal increase of the plasma current. According to a created statistical model, the most influential experimental parameters in the average power plasma density were output voltage, %CH4 in the gas mixture, and duty cycle. The surfaces were able to reduce the friction coefficient to values down to 0.08 and decrease the wear rate by 25 to 70 %, depending on their characteristics.

This study is focused on a detailed investigation of high-temperature corrosion and oxidation behavior of borided CoCrFeNiAl0.5Nb0.5 HEAs, considering their use in advanced engineering applications. CoCrFeNiAl0.5Nb0.5 HEA was produced by arc melting. XRD and SEM-EDS analysis before boriding determined that the alloy consisted of four different phases with different chemical compositions. Powder-pack boriding of a CoCrFeNiAl0.5Nb0.5 HEA was performed at 1000 °C for 3 h in a boriding media containing 90 % boron carbide and 10 % sodium tetrafluoroborate. As a result of the boriding process, complex boride layers consisting of (CoFe)B2, CrFeB, CoNbB, FeB and NiB phases were obtained on the surface with a thickness of 40 μm and hardness of 3004 HV. it was determined that the microstructure with cauliflower appearance evolved towards a dense and non-porous appearance around 20 μm as the boron diffusing into the HEA microstructure filling the gaps of intermetallic compound in the single structure, HEA and borided HEAs were each subjected to a cyclic hot corrosion test at 900 °C in molten corrosion salts of Na2SO4 and V2O5. After hot corrosion tests, long rod-like structures were observed in both samples due to the excessive corrosion, while borided alloys were more resistant to hot corrosion damage. After oxidation tests, HEA consists of a compact protective alumina scale that provided better oxidation resistance, while non-protective mixed oxides with cracks were dominant in the borided HEA.

Torch-substrate relative velocity is a plasma spray coating control parameter that affects lamellar thickness, heat transfer from the torch to the substrate, splat dispersion, and segmentation crack density. Within the thermal barrier coating and solid oxide fuel cell/solid oxide electrolysis literature, plasma sprayed coatings are rarely fabricated with velocities that exceed ~2 m s−1. Here, we explore the effect of torch-substrate relative velocities in the range of 4–20 m s−1 on crack density in thin (10–15 μm) solid oxide cell electrolyte coatings. Crack densities were observed to drop from ~2.4 to ~0.04 mm−1 by increasing the torch-substrate relative velocity from 4 to 16 m s−1. In agreement with previous studies performed at lower velocities, crack densities correlate well with plasma torch heat impulse. Full cells were fabricated using torch-substrate relative velocities of 12–20 m s−1.

The work herein describes the effect of the dispersion of ZrC and TiNi nanostructures, produced by mechanosynthesis, on the anticorrosion and tribological properties of epoxy resin (ER) coatings. Electrochemical impedance spectroscopy (EIS) showed that the addition of the nanostructured materials in the polymer matrix improved by three to four orders of magnitude the corrosion resistance of a pristine epoxy resin coated steel exposed to a 3.5 wt% NaCl solution. The chemical and nanocrystalline nature as well as the particle size of the reinforcements played an important role in the penetration of aggressive agents and corrosion of the steel. Interestingly, TiNi promoted a corrosion inhibiting effect through the deposition of its cations on the steel surface. On the other hand, scratch tests as well as electron and atomic force microscopy analysis revealed that the particle size of the reinforcements was a dominant effect on the scratch resistance of the nanocomposite coatings due to the modification of the surface roughness as well as the stress distribution during the scratch tests. The scratch resistance of the pristine epoxy resin was higher than that of the TiNi powder nanocomposite, but lower than that of the ZrC coating. In addition, ZrC promoted a lubricating effect during the scratch test. Up to ∼20 wt% of TiNi shape memory phase in TiNi reinforcement did not provide evident enhancement of the coatings scratch resistance.

In this study, oscillating wear tests were carried out on the high-speed laser metal deposited (HS-LMD) high-entropy alloys (HEAs) Al0.3CrFeCoNi, Al0.3CrFeCoNiNb0.5 and Al0.3CrFeCoNiMo0.75 at temperatures of 25 °C, 500 °C, 700 °C, and 900 °C. The microstructure was analyzed using scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). In addition, the crystal structure was investigated by X-ray diffraction (XRD). Furthermore, the Vickers hardness (HV0.1) was determined on cross-sections. All tests were performed before and after the high-temperature wear tests. The wear depth was measured using laser scanning microscopy. Increasing the temperature leads to decreased wear depth, particularly for the Nb- and Mo-containing HS-LMD coatings. The wear mechanisms change from abrasive, adhesive and oxidative wear to pronounced oxidative wear. The adhesion of the oxide layer is most important for high wear resistance at elevated temperatures. Strong adhesion is attributed to compact, thin and mechanical clamped oxide layers, which are found for the Nb-containing HS-LMD deposited coating resulting in the lowest wear depth.