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${\text{AlCoCrFeNi}}_{2.1}$$+$xwt.%TiC ($x=3$, 6, 9) coatings were prepared on H13 steel by laser cladding (LC) technology. It was characterized by a friction and wear test machine, optical microscope (OM), X-ray diffractometer (XRD), hardness tester, etc. The effects of different TiC contents on the microstructure and properties of ${\text{AlCoCrFeNi}}_{2.1}$ coatings were analyzed. The results show that the coating microstructure without TiC addition is dominated by coarse columnar crystals and dendrites. After the addition of TiC, the coated massive crystals and equiaxed crystals become finer. XRD analysis reveals that the phase structure of the coating has FCC, B2 solid solution phase and TiC-reinforced phase. TiC phase can significantly improve the hardness of the coating. The microstructure reveals that fine TiC particles are widely distributed among the dendrites of the FCC matrix. The hardness and friction wear experiments revealed that the average hardness of the coatings with TiC has increased significantly compared to that of the substrate. The hardness of the ${\text{AlCoCrFeNi}}_{2.1}$ with 9%TiC coating increased by 184.6% compared to that of the substrate. The friction coefficient was the smallest at 0.748. The lowest self-corrosion current was $9.040\times 10^{-7}$$\mathrm{\text{A}}\cdot {\mathrm{\text{cm}}}^{-2}$. The ${\text{AlCoCrFeNi}}_{2.1}$ with 9%TiC coating had the best corrosion resistance.

Lawsonia inermis Linn Leaf extract has been evaluated in alkaline solutions for its influence on electroless Ni–P alloy deposition on mild steel. During electroless plating, the effect of experimental processing conditions on deposition rate is investigated. Bath compositions and operational parameters have been optimized. The findings indicate that increasing the volume of additives from 0.5mL to 5mL improves the inclusion rate of electroless Ni–P alloy coating. In the absence of a complexing agent, additive Lawsone exhibits additional structural features and phases. The deposition rate and the corrosion rate of the Ni–P deposits were estimated, respectively, from the weight loss after a period of time. It is recommended to replace sodium citrate with Lawsone.Lawsone’s effect acting as a complexing agent on Ni–P electroless coating was explored utilizing SEM, EDAX, AFM, FTIR, and XRD, as well as corrosion investigations. Polarization and electrochemical impedance spectroscopy are used to assess the corrosion efficiency.

In order to obtain better corrosion resistance, the micro-arc oxidation (MAO) coating after adding (Y(NO₃)${}_3\cdot 6$H₂O was sealed by TiO₂ sol–gel method. Dynamic polarization curves and electrochemical impedance spectroscopy show that the prepared samples (Y(NO₃)${}_3\cdot 6$H₂O content was 1.5g/L) have good corrosion resistance ($1.2308\times 10^{-9}$A$\cdot {\mathrm{\text{cm}}}^{-2}$) in 3.5wt.% NaCl aqueous solution. Afterward, the samples with a concentration of 1.5 g/L of Y(NO₃)${}_3\cdot 6$H₂O were sealed by TiO₂ sol–gel. Through SEM, XRD and electrochemical test, it is found that the surface of the film is smooth, the phase is mainly in the form of Anatase-TiO₂ and has better corrosion resistance ($7.593\times 10^{-9}$A$\cdot {\mathrm{\text{cm}}}^{-2}$). This showed that sealing the doped 2024 aluminum alloy MAO film can significantly reduce the corrosion sensitivity and corrosion rate of the film.

Super-hydrophobicity inspired by natural water-repellent surfaces has received tremendous attention for surface functionalization of metallic materials in many applications. Problems of corrosion and/or contamination that happens on the surface can be partially solved as the material obtained super-hydrophobicity. Appropriate surface pattern and low surface energy are the two key factors that can realize super-hydrophobicity. In the present paper, laser surface texturing (LST) followed by decoration of Hexadecyltrimethoxysilane (HDTMS) was conducted to manipulate the super-hydrophobicity and corrosion resistance of AISI 316 stainless steel (SS) on the surface. Scanning electron microscopy (SEM) and an ultra-depth field microscope were employed to characterize the surface morphologies of the received samples before and after corrosion tests. Corrosion resistance and super-hydrophobicity for the related samples were investigated using electrochemical tests and water contact angle measurements. It was found that various surface patterns differed with intervals (250, 150, 80, and $d=50\mu$m,) between two micro-dimples have formed on 316 SS sample surfaces after LST treatment. The surface roughness values gradually increased with the decrease of interval. The 316 SS samples obviously reduced surface energy values after HDTMS decoration. In simulated haze solution, electrochemical tests demonstrated that the 316 SS sample treated with $\mathrm{\text{HDTMS}}+\mathrm{\text{LST}}$ (HT-316 SS, $d=50\mu$m) exhibited lower corrosion and higher corrosion potential current density than the smooth 316 SS (S-316 SS), $\mathrm{\text{HDTMS}}+\mathrm{\text{S}}$-316 SS (HS-316 SS), and LST 316 SS (T-316 SS, $d=50\mu$m) samples. As expected, the HT-316 SS ($d=50\mu$m) exhibited the highest water contact angle of 155.85^∘ as compared to HS-316 SS and other HT-316 SS samples. Meanwhile, the superhydrophobic surface of HT-316 SS ($d=50\mu$m) exhibits super-oleophilic and self-cleaning properties.

The 6061-aluminum alloy is anodized by pulse anodizing method in the solution with sulfuric acid and oxalic acid to improve its corrosion resistance and mechanical properties greatly. Different duty cycles ranging from 0.2 to 0.8 are applied during the pulse anodizing process to study the influence of duty cycles on the thickness, roughness, composition, surface morphology, corrosion, and wear resistance performance of the oxide films obtained on the surface of 6061 aluminum alloy. The anodizing process of aluminum alloy in an acid solution is accompanied by the formation and dissolution of oxide film. The duty cycle impacts the thickness and roughness of the oxide film. With the increase of the duty cycle from 0.2 to 0.6, the thickness of the oxide film is increased from 21.2 to 38.7$\mu$m while the roughness of the oxide film gradually increases from 0.237 to 0.674$\mu$m. However, the thickness of the oxide film is decreased obviously to 31.1$\mu$m when the duty cycle applied is 0.8 due to thermal effects and stress-induced cracking. The surface of oxide films presents many pores and agglomerated alumina composed of the elements of aluminum (Al), oxygen (O), sulfur (S), and carbon (C). A higher duty cycle is beneficial to increase the growth rate and size of agglomerated alumina on the surface of the oxide film. Some micro-cracks can be observed on the surface of the oxide film anodized using a 0.8-duty cycle. After the pulse anodizing treatment, the hardness of anodized aluminum alloys improves significantly. With the increase of the duty cycle from 0.2 to 0.8, the hardness of the oxide film ranged from approximately 300–550HV. The oxide film anodized using a 0.6 duty cycle presents the best wear resistance and optimal corrosion resistance with the smallest wear rate of 1.043 × 10${}^{-5}$mm³/Nm and the smallest corrosion current density of 9.73$\mu$A/cm².

The Zr-doped TiN coating, a nanometer (Ti, Zr)N thin film, has been deposited by reactive magnetron sputtering on slides and Al substrates. The crystalline phase and energy band structure have been analyzed by XRD and STS. The results of XRD show that the (Ti, Zr)N film is poly crystalline and consisted of mixed crystal of TiN and ZrN phase. The STS spectra show that Zr-doping didn't change the position and band-gap of energy level, only two new energy levels appeared, E_g = 0.33eV and E_g = 0.42eV. According to the results of measurement, (Ti, Zr)N has higher hardness and better corrosion resistance than TiN by Zr-doping.

Composite coatings constitute a new class of materials which are mostly used for mechanical and tribological applications. The corrosion resistance of these composite coatings, however, has not been systematically studied and compared. In this study, electroless Ni–P composite coatings are formed on St37 steel through the addition of nano-scale SiC particles to the plating bath. This work aimed to investigate the corrosion characteristics of electroless nickel composite coatings using electrochemical measurements which include polarization and electrochemical impedance spectroscopy tests. The morphology and structure of the composite coatings were studied by scanning electron microscopy (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The results showed that both electroless nickel and electroless nickel composite coatings demonstrated significant improvement of corrosion resistance in salty atmosphere.

The duplex Nickel–Boron–Titania/Nickel (Ni–B–TiO₂/Ni) coatings were deposited on mild steel by using two baths with Ni as the inner layer. TiO₂ nanoparticles were incorporated into the Ni–B coatings as the outer layer by using solid particle mixing method. The microstructure, morphology and corrosion resistance of the duplex Ni–B–TiO₂/Ni nanocomposite coatings were systemically investigated. The results show that the duplex interface was uniform and the adhesion between two layers was very good. The microhardness of duplex Ni–B–TiO₂/Ni coating was much higher than the Ni coating due to the outer layer of Ni–B–TiO₂ coating. The corrosion resistance of the duplex Ni–B–TiO₂/Ni coating was also significantly improved comparing with single Ni–B coating. The Ni–B–10 g/L TiO₂/Ni coating was found to have the best corrosion resistance among these duplex coatings. This type of duplex Ni–B–TiO₂/Ni coating, with high hardness and good corrosion resistance properties, should be able to find broad applications under adverse environmental conditions.

Rare earth has been widely used in materials manufacturing to improve hardness and toughness. In this paper, conventional, nano-modified and CeO₂ modified WC-12Co coatings are produced by using high speed oxygen flaming (HVOF) spraying technology. Long-term immersion and electrochemical tests of these coatings in 3.5 wt.% NaCl solution are conducted. The surface morphologies were observed to investigate the corrosion mechanisms. The results show CeO₂ modified WC-12Co coatings to possess the best corrosion resistance but the nano-modified WC-12Co coating has the worst performance. Results suggest that the improvement of corrosion resistance for CeO₂ modified WC-12Co coating can be attributed to the enhancement of interfacial strength between Co binder phase and WC particles.

Developing amorphous alloys with good corrosion resistance has attracted wide interests recently. In this work, a series of Fe${}_{73.5-x}$Ni${}_x$Cu₁Nb₃Si${}_{13.5}$B₉ ($x=0$, 1, 2, 3 and 4 at.%) amorphous alloys are fabricated. The influence of Ni addition on the structure and corrosion resistance of the alloys in KNO₃ solution was investigated. The amorphous ribbons showed excellent corrosion resistance due to the formation of a stable passive film that ensured a very large passivation plateau. The corrosion resistance is sensitive to the minor addition of Ni ($\le$4 at.%), which significantly improved the corrosion resistance according to the results of electrochemical measurements.

Anodized aluminum (Al) and Al alloys have a wide range of applications. However, certain anodized finishings have relatively low hardness, dull appearance and/or poor corrosion resistance, which limited their applications. In this research, Al was first electropolished in a phosphoric acid-based solution, then anodized in a sulfuric acid-based solution under controlled processing parameters. The anodized specimen was then sealed by two-step sealing method. A systematic study including microstructure, surface morphology, hardness and corrosion resistance of these anodized films has been conducted. Results show that the hardness of this new anodized film was increased by a factor of 10 compared with the pure Al metal. Salt spray corrosion testing also demonstrated the greatly improved corrosion resistance. Unlike the traditional hard anodized Al which presents a dull-colored surface, this newly developed anodized Al alloy possesses a very bright and shiny surface with good hardness and corrosion resistance.

It is important that the steel plate is manufactured with a high tensile strength to reduce the weight of the body. It is generally accepted that twinning induced plasticity (TWIP) steel is a special steel with not only a high ductility but also a high-tensile strength compared to general steel. While numerous investigations have been carried out on the TWIP steel with an amount of manganese of at least 20%, the investigation of steel with manganese content of less than 20% has seldom been considered until now. In this study, the TWIP steel with manganese of less than 20% (12Mn, 15Mn and 18Mn TWIP steel) was investigated to determine the corrosion properties using electrochemical method. The 18Mn and 12Mn samples exhibited the best and worst corrosion resistance, respectively. It is suggested that the 18Mn sample forms a stable oxide film on the surface because it contains a larger amount of manganese and aluminum compared to the other samples, and their composition enables the easy formation of the oxide film.

Fe-based amorphous alloys are important materials with a high potential for commercialization by evaluating their corrosion performances. In this work, amorphous Fe${}_{73.5}$Cu₁Nb₃Si${}_{13.5}$B₉ alloy was chosen as a target material to investigate the effects of the addition of C on the corrosion properties by an electrochemical method. Alloy ingots Fe${}_{73.5}$Cu₁Nb₃Si${}_{13.5}$C${}_x$B${}_{9-x}$ (x = 0, 1, 2, 3 at.%) were prepared using an arc melting system, under argon atmosphere. Planar flow melt spinning of the alloys was carried out to obtain amorphous ribbons of the width $\sim$5 mm and the thickness about 30 $\mu$m. Effects of the addition of C into Fe${}_{73.5}$Cu₁Nb₃Si${}_{13.5}$B₉ amorphous soft magnetic alloys were investigated in acidic solutions. Studies of potentiodynamic polarization and electrochemical impedance revealed the passivation ability and corrosion resistance of the amorphous ribbons with C in the 0.1M H₂SO₄ media at room-temperature. The amorphous ribbons showed excellent corrosion resistance with formation of a stable passive film. It can be obviously observed that the addition of C significantly improves the corrosion resistance.

Multi-direction isothermal forging of 7050 aluminum alloy at 10³s¹ strain rate and temperature of 300⁰C are observed. EBSD is used to characterize the grain structure, and the Vickers hardness and intergranular corrosion (IGC) properties are tested. The results of EBSD indicate that the sub-grains increase and the grain size decreases gradually as the pass of isothermal forging increases. The volume fraction of sub-grain has great effect on the corrosion resistance. The more sub-grains are included in the grain structure, the better the corrosion resistance and the mechanical properties. The grain size also influences the corrosion resistance, and the decreasing of the grain size is adverse to the corrosion resistance but is good for mechanical properties.

The Ni–Zn–P alloy coating has excellent physical and chemical properties that have been exploited for various industrial applications. Using sodium citrate as a complexing agent and lactic acid as a stabilizer, the effects of temperature and pH on the deposition rate and corrosion resistance of electroless plated Ni–Zn–P coating were studied. The results indicated that, when the temperature was 85${}^{\circ }$C, a good deposition rate was obtained with stable plating solution. pH value of 9.0 is preferred for the coating process by considering the stability of plating bath and deposition rate. The Ni–Zn–P alloy coating deposited with plating temperature of 85${}^{\circ }$C and bath pH of 9.0 has good quality, and a uniform and smooth surface texture without porosity.

Duplex Ni-P-TiO₂/Ni coatings were deposited on the brass substrate by using two baths. Ni-P-TiO₂ nanocomposite coatings were electroplated as the outer layer on the Ni-plated brass substrate by adding transparent TiO₂ sol (0–50 mL/L) into the Ni-P plating solution. The microstructure, mechanical property and corrosion resistance of the duplex Ni-P-TiO₂/Ni nanocomposite coatings were systemically investigated. The results show that the interface of duplex coating was uniform and the adhesion between two layers was extremely good. The microhardness of duplex Ni-P-12.5 mL/L TiO₂ /Ni coating was $\sim$616 HV${}_{50}$ compared to $\sim$539 HV${}_{50}$ of Ni-P /Ni coating and $\sim$307 HV${}_{50}$ of single Ni coating. Meanwhile, the wear resistance and the corrosion resistance of the duplex nanocomposite coating have also been improved remarkably compared with single Ni coating. However, adding excessive TiO₂ sol (more than 12.5 mL/L) caused the agglomeration of TiO₂ nanoparticles and led to a porous structure in the outer layer, resulting in the deterioration of coating properties.

Titanium nitride (TiN) thin films have excellent physical and chemical properties, and are widely used as cutting tools, drills and die protective coatings. However, their limited hardness and corrosion resistance caused by the rough, loose, columnar structure will affect its application in extreme environments. TiN films with refined grains and nanostructure might solve this problem. In this paper, Co and Cr atoms were doped into TiN film to tailor its structure. The effects of Co and Cr content on the Ti(CoCr)N film structure, mechanical properties and corrosion resistance were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), microhardness tester and electrochemical corrosion tester. The results show that Co and Cr doping can disturb the columnar growth of TiN films, and lead to refinement of TiN grains. Compared to TiN films without Co and Cr doping, the hardness of Ti(CoCr)N with 2.7 at.% Co and 1.9 at.% Cr increases by about 37% to 31.3 GPa. And Ti(CoCr)N films with 2.7 at.% Co and 1.9 at.% Cr have the best corrosion resistance.

In order to obtain a laser-cladded coating with no cracking and good corrosion resistance, this paper investigated laser cladding of a mixture of 17-4PH stainless steel and Ni60 powders on ASTM 1045 steel substrate. The surface cracking, mechanical properties and corrosion resistance of the coatings were assessed by various characterization methods. The experimental results demonstrated that a crack-free coating can be obtained by adding 30% (or above) 17-4PH stainless steel into Ni60 alloy. The mechanical properties of the coatings were determined by adding 17-4PH, but stabilized at about 79% of pure Ni60 alloy, which is acceptable considering the benefit of elimination of surface cracking. Decrease in the mechanical properties were caused by the dilution of the strengthening elements and reduction of population of hard phases. Composite coating having 30% of 17-4PH also exhibited the smallest corrosion current, lowest corrosion potential and slowest corrosion rate, and therefore the best corrosion resistance.

Amorphous Ni–W–P coatings were prepared by electroless plating and annealed at 250${}^{\circ }$C for different times to obtain different microstructures. The local atomic structure of these amorphous coatings was analyzed by calculating the atomic pair distribution function from the XRD patterns. The type of crystals in coatings was obtained from the TEM image and corresponding selected area diffraction (SAED) pattern. The proportion of microscopic particles in the matrix was roughly estimated from the first DSC exothermic peak area. Corrosion resistance in 0.5-M sulfuric acid solution was investigated via electrochemical techniques. Experimental results showed that all annealed coatings still held amorphous structure, albeit the microstructure had been changed. The correlation radius and the atomic number of clusters had increased, especially when the annealed time extended to 12 h and 20 h. The number of microscopic particles in the amorphous matrix also increased with rise in heat treatment time. The type of crystals in these amorphous matrices increased from Ni/Ni (W) to Ni/Ni (W), Ni₁₂P₅ and Ni₅P₄. The decreasing corrosion resistance was in agreement with the increasing number of microscopic particles and higher-order clusters in annealed Ni–W–P coatings. These microscopic particles could form micro-galvanic cells in corrosion solution. The higher-order clusters increased the composition difference in the amorphous matrix, and this also promoted to form micro-galvanic cells in solution.

Porous Ni–Ti alloys were fabricated by reactive synthesis of Ni and Ti elemental powders. The corrosion behavior of porous Ni–Ti alloys was explored by electrochemical methods and weight change measurements at 298 K in seawater. The polarization curves and electrochemical impedance spectroscopy data show that porous Ni–Ti (6.5:3.5) alloys provide the best corrosion resistance. The values of corrosion current density and corrosion rate are 1.6944 × 10⁻⁴ mA/cm² and 1.9929 mm/a, respectively. The corrosion behavior and corrosion mechanism of porous Ni–Ti alloys are also discussed.