Alloy Coatings Research Articles

Microstructure and corrosion properties of CrMnFeCoNi high entropy alloy coating by temperature field-assisted laser cladding

The CrMnFeCoNi high entropy alloy coatings were prepared on the surface of Q345 steel using a temperature field-assisted laser cladding process, and the effects of the applied temperature field on the cladding coatings were studied. The microstructures and corrosion morphologies of the coatings were observed, and the elemental distribution, hardness, effective elastic modulus, electrochemical corrosion performance, and corrosion products of different coatings were analyzed. The results show that the porosity of the HEA coatings prepared with a temperature field is reduced to below 50 % of the initial level. The microstructure of the coating changed, with the nanoindentation hardness of the coating increasing by up to 0.55 GPa, enhancing the mechanical properties. Among all the coatings, the coating prepared at 250 °C temperature field exhibited the best corrosion resistance, with corrosion potential and current density of −0.27 V and 0.15 μA/cm2, respectively, improving the corrosion potential by 0.1 V and reducing the current density by 1.08 μA/cm2 compared to the sample prepared at room temperature. After incorporating the temperature field, the stability of the passive film on the coating during corrosion improved, and the nucleation rate of pitting decreased. Therefore, incorporating an appropriate temperature field during laser cladding can effectively enhance the overall performance of the CrMnFeCoNi HEA coating.

Deposition, microstructure and hardness of AlCoCrFeNi2.1 eutectic high entropy alloy coatings by cold spray, HVOF, and plasma spray

Eutectic high entropy alloys (EHEAs) are reported to exhibit excellent mechanical properties which are useful for coating applications. In this study, we have produced AlCoCrFeNi2.1 EHEA coatings using the cold spray, high velocity oxygen-fuel (HVOF), and plasma spray techniques and compared their bonding characteristics, microstructure and hardness. We observe body-centered cubic (bcc) to face-centered cubic (fcc) phase transformations in all the types of coatings. The high processing temperatures in HVOF and plasma sprays lead to the segregation and depletion of Al from Ni-and Al-rich bcc/B2 regions and form Al2O3. In the cold sprayed coatings, we observe that a fraction of lamellar microstructure is preserved after cold spraying. Regarding the hardness, the cold sprayed coatings exhibit hardness in the range of 440–498 HV due to high work hardening and low oxygen content below 4 at.%; the HVOF coatings show the hardness in the range of 380–556 HV due to the effects of oxide dispersion strengthening with 13–28 at.% oxygen; The plasma sprayed coatings exhibit the hardness in the range 208–258 HV and 6.1–13.4 at.% oxygen. This study demonstrates the feasibility to produce thick and dense EHEA coatings using the above spray techniques, and the cold sprayed coatings exhibit relatively high hardness and low oxygen levels.

Preparation process, surface properties and mechanistic study of HVAF-sprayed CoCrFeNiMo0.2 high-entropy alloy coatings

The objective of this study is to develop infrared reflective coatings with excellent service performance in extreme environments, aimed at reducing system energy consumption and enhancing service life. In this work, CoCrFeNiMo0.2 high-entropy alloy (HEA) powder was deposited on the 316 L stainless steel (SS) substrate using High-Velocity Air Fuel (HVAF) thermal spray technology. The microstructure, mechanical properties, infrared reflectivity, and corrosion resistance of the coatings under different spraying parameters were investigated and compared with those of the substrate. Computational Fluid Dynamics (CFD) simulation was employed to analyze the influence of HVAF spraying parameters on flame characteristics and particle flight behavior, providing guidance for optimizing the spraying process and explaining underlying mechanisms. Results demonstrated that adjusting parameters such as propane and air pressure, spraying distance, and powder feed rate could produce dense coatings with <1 % porosity. The microhardness of the coatings was approximately 1.8 times that of the substrate, and the bonding strength between the coating and the substrate is increased to 39.4 MPa. Additionally, the near-infrared reflectivity of the coatings was significantly higher than that of the substrate, with an enhancement of 18.7 %. Coatings sprayed under different parameters exhibited superior passivation and pitting corrosion resistance compared to the substrate in 3.5 wt% NaCl and 1 mol/L HCl solutions. Optimization of spraying parameters further enhanced the protective capability of the passivation film and corrosion resistance. Consequently, CoCrFeNiMo0.2 HEA coatings prepared by HVAF spraying technology demonstrate excellent comprehensive performance, holding promising potential for industrial applications.

High-strength and wear-resistant Babbitt alloy coatings prepared through in-situ alloying

Babbitt alloy, a commonly used wear-resistant coating material, has a low hardness. This causes severe plastic deformation, detachment or heavy wear to easily occur under low speed and heavy-load service conditions, reducing its service life. To solve these problems and improve the bonding strength and wear resistance of the tin-based Babbitt alloy coating, a higher laser cladding power was adopted to achieve in-situ alloying of the cladding layer and enhance the strength of the coating. The increase in strength was verified through the Fleischer theory and Orowan empirical formula to mainly result from the enhancement of solid solution strengthening and dispersion strengthening. Meanwhile, due to dispersion strengthening and the presence of dendritic FeSn, the occurrence of delamination wear was effectively prevented. The bonding strength of the final sample reached 147 MPa, and the wear rate was as low as 4.24 × 10–5 mm3/N・m. Thus, a high-strength and wear-resistant Babbitt alloy cladding layer was obtained.

Protective properties of chromate-free conversion coatings for copper-containing aluminum alloys in tropical climates

Protective properties of chromate-free conversion coatings for copper-containing aluminum alloys in tropical climates

Investigation on Microstucutres and properties of ion nitriding layer of Al0.5CoCrFeNiTi0.25 HEAs cladding coating

To investigate the effect of ion nitriding on the microstructures and properties of high entropy alloy coatings, the Al0.5CoCrFeNiTi0.25 high entropy alloy coating was fabricated via laser cladding and subsequently subjected to ion nitriding treatment. A comparative analysis were conducted to investigate the phase compositions, microstructures and properties of cladding coatings and ion nitriding layer. Furthermore the formation mechanism of the nitriding layer was studied. XRD results revealed that Al0.5CoCrFeNiTi0.25 HEA coatings consisted of duplex FCC and BCC phases, whereas the nitriding layer was composed of high-nitrogen FCC solid solutions and nitrides such as AlN, CrN, Fe4N and TiN. Following ion nitriding, the surface morphology of nitriding layer presented “cauliflower-like” nitride particles, which became denser with the extended nitriding time. Notably, the microhardness of nitriding layer was approximately four times that of HEA coating, and the wear resistance and the corrosion resistance of cladding coating were improved significantly after ion nitriding. During ion nitriding process, N atoms reacted with the alloying elements to form nitrides, which preferentially deposited at grain boundaries and BCC phases and grew horizontally. As the deposition layer spread across the entire surface, the nitriding mechanism shifted from reaction -controlled to diffusion-controlled, with N atoms diffusing inward to form a diffusion layer with high nitrogen solid solutions. With the prolong of nitriding time from 1h to 12h, the thickness of the diffusion layer increased from 11.77 μm to 96.07 μm.

STRUCTURE FORMATION OF Ni−P ALLOY ELECTROCOATINGS WITH INCREASED CORROSION RESISTANCE

Purpose of research. The main factors that reduce the protective properties of electrocrystallized coatings are the formation of volumetric defects − pores, as well as the occurrence of microgalvanic couples at grain boundaries, that is, on surface defects of the crystalline structure. Creating a non-porous structure in electrocoatings, eliminating the formation of surface defects in metal/alloy layers, as well as the possibility of replacing chromium coatings, which are obtained from toxic electrolytes, are urgent tasks. Materials and methodology. In the work, it was proposed to use electrocoatings with Ni−P alloy as protective layers on products that increase corrosion resistance. An X-ray determination of the phase composition of Ni−P electrochemical deposits was carried out. The surface morphology and corrosion resistance of coatings were studied. Results. Samples of electrochemical coatings of pure nickel and nickel-phosphorus alloy were studied. It has been established that during the formation of nickel coatings with the addition of phosphorus ions, the surface morphology has practically no pores, amorphization of deposits occurs, due to which the protective properties, namely, corrosion resistance, are improved. Scientific novelty. Factors have been identified that influence the increase in corrosion resistance of coatings − the absence of a porous structure and the formation of an amorphous state. Conclusions. The influence on the structure and properties of electrochemical coatings of a nickel-phosphorus alloy has been studied. It has been established that the addition of phosphorus ions to the nickel plating electrolyte leads to the formation of an amorphous structure in the coatings, and layers of the Ni−P alloy appear practically without the presence of pores. It has been established that the effect of increasing the corrosion resistance of the electrochemical coating with a nickel-phosphorus alloy (by 30 %) is due to the formation of an amorphous structure of the solidifying metal liquid while preventing the crystallization process during electrochemical deposition.

Superhydrophobic nickel/manganese alloy coatings on carbon steel with corrosion resistance and robustness capabilities prepared via one-step electrodeposition method

Superhydrophobic nickel/manganese alloy coatings on carbon steel with corrosion resistance and robustness capabilities prepared via one-step electrodeposition method

Substantial enhancement of AlCoCrFeNiTiWC high-entropy alloy coating performance under water cooling and pulsed laser

AlCoCrFeNiTiWC high-entropy alloy (HEA) coatings were prepared using laser cladding technology with continuous laser and air cooling, as well as pulsed laser with water cooling. The phase structures of the coatings were BCC, (Ti,W)C, and μ phase. The carbides and μ phase in the pulsed laser with water-cooled coating were refined, and the proportion of the μ phase decreased. The wear resistance of the pulsed laser with water-cooled coating significantly increased, which can be attributed to the reduction in the proportion of μ phase, the refinement of carbides, and the formation of a wear lubrication layer. The pulsed laser with water cooling enhanced the thickness and uniformity of the passivation film on the coating surface, thereby improving corrosion resistance.

Effects of Scanning Speed on the Microstructure and Wear Properties of Rockit 606 Coating Layer by Disk Laser Cladding.

Improving the wear resistance and corrosion resistance of 60Si2Mn steel is an important issue in agricultural machinery. A Rockit 606 coating layer may exhibit excellent performance in wear resistance and corrosion resistance. However, there are very a few public reports and articles involving the topic of a Rockit 606 laser cladding layer on a steel 60Si2Mn surface. It is of great importance to research Rockit 606 laser cladding layers. This work focuses on studying the microstructure and properties of Rockit 606 coating layers with different scanning speeds by disk laser cladding. Firstly, the laser cladding platform was designed and set up. Secondly, the laser cladding parameters were designed, and then the laser cladding experiment was conducted, and the Rockit 606 coating layers were obtained. And finally, the microstructure, phase distribution, corrosion resistance, surface hardness, and wear resistance of the coating layers were measured and analyzed. A scanning electron microscope (SEM), X-ray diffractometer (XRD), electrochemical workstation, and microhardness tester were used in this work. It was found that the microstructure Rockit 606 alloy coating consists of γ-Fe, V8C7, and Cr7C3. The microhardness of the Rockit 606 alloy coatings decreased with an increase in the scanning speed. When the scanning speed was 4 mm/s, the highest microhardness value reached 867.2 HV, which is about three times of that of the substrate. The average coefficients of friction (COFs) of the coatings decreased with an increase in the scanning speed, which led to the corresponding decrease of the wear rate. When the scanning speed was 4 mm/s, the wear behavior of the coating was mainly oxidative wear and a small amount of adhesive wear. The self-corrosion current density of the coatings prepared by laser cladding in a 3.5 wt.% NaCl solution is one order of magnitude lower than that of the substrate, indicating that the coatings have better corrosion resistance properties.

Enhanced hot corrosion resistance of AlCoCrFeNi2.1 high entropy alloy coatings by extreme high-speed laser cladding

Extreme high-speed laser cladding (EHLC) and multiple laser remelting (EHLC-MR) are used to improve hot corrosion resistance of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) coatings by refining their microstructures, introducing low angle grain boundaries (LAGBs) and high densities of dislocations as well as higher compressive residual stresses (CRSs) in the coatings. The experimental results show that finer microstructure, more LAGBs and high densities of dislocations are beneficial to increase Al2O3 nucleation sites and promote the uniform formation of the oxide layer on the coating surface. On the other hand, higher CRSs suppress the initiation and propagation of cracks as well as enhance the adhesion between the oxide layer and the substrate. Thus the hot corrosion resistance of the EHEA coatings under a molten salt of 75% Na2SO4 + 25% NaCl at 900°C is improved significantly. These novel results provide effective approach for designing elevated-temperature materials.

Surface morphology evolution, microstructural response and mechanical property variation of Au-ion irradiated CrNbZrMoV, TiCrZrMoV, TiNbCrMoV, TiNbZrCrV and TiNbZrMoCr high-entropy alloy coatings

In this work, the CrNbZrMoV, TiCrZrMoV, TiNbCrMoV, TiNbZrCrV and TiNbZrMoCr refractory high-entropy alloy (RHEA) coatings (1.67∼2.77 μm of thickness) were prepared by magnetron sputtering. Then, 6 MeV Au-ion irradiations with 2.5 × 1015 to 1.0 × 1016 ions/cm2 fluences were performed on these coatings at 473 K, and the surface morphology, microstructure and mechanical property were investigated. The peak damage of the CrNbZrMoV, TiCrZrMoV, TiNbCrMoV, TiNbZrCrV and TiNbZrMoCr coatings under 1.0 × 1016 ions/cm2 fluence are 48, 48, 44, 48 and 48 dpa, respectively. The peak Au concentration of the CrNbZrMoV, TiCrZrMoV, TiNbCrMoV, TiNbZrCrV and TiNbZrMoCr coatings under 1.0 × 1016 ions/cm2 fluence are 4.27 × 103, 4.12 × 103, 4.13 × 103, 4.16 × 103 and 4.37 × 103 appm, respectively. The surface morphology of the CrNbZrMoV, TiCrZrMoV, TiNbZrCrV and TiNbZrMoCr coatings were smoothed obviously. For BCC TiNbCrMoV coating, irradiation caused the growth of the nanocrystalline. For amorphous coatings, the crystallization occurred in the CrNbZrMoV, TiCrZrMoV and TiNbZrMoCr coatings after 2.5 × 1015 fluence irradiation (≥12 dpa), while the TiNbZrCrV coating remain mainly amorphous structure after all irradiation. It was found that irradiation induced continuous crystallization occurred not only at the surface but also in the peak damage zone of the coating, and then grew inside the irradiated region. Apparent irradiation hardening was observed in all the coatings except the TiNbZrCrV coating. The structural stability of these coatings under the current irradiation condition was discussed. Preliminary study shows that the great irradiation tolerance of amorphous TiNbZrCrV coating may be related to the lowest electronegativity difference (Δχ = 0.121) and large atomic size difference (δ = 9.042 %) that stabilize the structure and inhibit atomic diffusion, respectively. These findings provide the guidance for the development of high irradiation tolerance materials for future nuclear energy applications with great structural stability.

Effect of Ti and Mo content changes on microstructure and properties of laser cladding FeCoCrNiMn high entropy alloy coatings

The HEA coatings of FeCoCrNiMnTixMo1.5-x(x = 0.25, 0.5, 0.75, 1 and 1.25) were prepared by laser cladding. X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and scanning electron microscopy (SEM) were used to characterize the phase and crystal structure. The mechanical properties were tested. The results show that Ti is solidly dissolved in the FCC phase for solid solution strengthening. Mo is precipitated as the second phase σ phase for second phase dispersion strengthening. As x increases, the coating becomes the FCC+σ phase, and the σ phase disappears at x = 1.25. The microhardness and wear resistance of the coating are greatly improved by solution strengthening and second phase precipitation strengthening. The microhardness is up to 3.18 times of the substrate, and the wear resistance is up to 10.9 times of the substrate. Corrosion resistance of all coatings is better than that of 45# steel. With the increase of x, the corrosion resistance of the coating increases first and then decreases. When x = 1, the corrosion resistance of the coating is the best.

Preparation of graphene/AlCoCrNiTiMox coatings by laser parameter optimization based on TRIZ theory and its application in extending the service life of surveying and mapping drones

During the use of surveying and mapping drones, their aluminum (Al) alloy body is prone to corrosion and has certain requirements for mechanical properties. In order to extend the service life of surveying and mapping drones, this study uses laser cladding technology to prepare graphene (Gr) reinforced AlCoCrNiTiMox high entropy alloys (HEAs) coatings on the Al alloy surface of the drone body. In order to optimize the laser preparation parameters, the Invention Problem Solving Theory (TRIZ) is introduced. By utilizing innovative tools such as physical contradictions, technical contradictions, and material field models of this theory, the preparation process parameters such as laser power, laser scanning speed, laser spot diameter were optimized. The microstructure of the coatings were analyzed using scanning electron microscope (SEM), transmission electron microscope (TEM), electron back scatter diffraction (EBSD), etc. The corrosion resistance, hardness and wear resistance of the coatings were tested. The experimental results show that the microstructure of Gr/AlCoCrNiTiMox alloy is mainly composed of equiaxed grains and molybdenum-chromium (Mo-Cr) precipitates. The Gr/AlCoCrNiTiMox HEAs exhibits excellent corrosion resistance in 0.5 mol/L H2SO4 solution. The corrosion resistance of alloys is related to their composition, the effects of Gr and Mo elements. Under the combined effects of solid solution strengthening, precipitation strengthening, Mo element and Gr, the mechanical properties of Gr/AlCoCrNiTiMox alloys are excellent. The hardness of Gr/AlCoCrNiTiMo0.1 and Gr/AlCoCrNiTiMo0.2 alloys are 685 HV and 736 HV, respectively, with average friction coefficients of 0.64 and 0.58, respectively. The effect of Mo element makes the grain size of Gr/AlCoCrNiTiMo0.2 alloy smaller than that of Gr/AlCoCrNiTiMo0.1 alloy, resulting in better mechanical properties and corrosion resistance. The research results indicate that laser cladding of Gr/AlCoCrNiTiMox coating on the Al alloy surface of drone fuselage provides assurance for extending its service life.

Microstructure and tribological performance of novel Ni-based alloy cladding with excellent high temperature wear resistance and self-lubrication performance

This paper aims to study the laser cladding of Ni-based alloy coatings with excellent high temperature wear resistance and self-lubrication performance on the surface of parts such that meet complex metallurgical service conditions. The composite alloy powders were formed by adding 3 wt%–11 wt% WS2 and Ti powder to NiCrCoMoBSi alloy powder, and the novel Ni-based alloy samples with high temperature wear resistance and self-lubrication performance were cladded on the surface of Cr28Ni48W5 substrate by laser cladding. The results show that the addition of WS2 and Ti powder had a significant influence on the microstructure evolution and high temperature wear resistance and self-lubrication performance of the samples. The laser cladding coating with 7 wt% WS2 and Ti had the 3 % TiS self-lubricating phase and 19 % enhanced phase with the best microstructure matching relationship, which improved the high temperature wear resistance and self-lubrication performance of the sample. At 800 °C, compared with the Cr28Ni48W5 superalloy substrate, the friction coefficient of the laser cladding coating was 0.22 and the wear ratio was 1.70 × 10−5 mm3 N−1 m−1, which were reduced by 60 % and 54.67 % respectively. The mechanism of the enhanced wear resistance and self-lubrication performance was elaborated.

Optimizing Cold Spray Parameters for High Entropy Alloy Coatings Using Taguchi and Box–Behnken Design Approaches for Mechanically Alloyed Powder

AbstractThe present study focused on optimizing the cold spray (CS) process parameters for depositing Fe20Cr20Mn20Ni20Co20 (Cantor alloy) coatings using mechanically alloyed (MA) powder. A two-step design of experiments approach was employed, beginning with the initial screening of input variables using the L8 Taguchi method, followed by the refinement of process parameters through the Box–Behnken design of experiments. Key performance indicators included deposition efficiency (DE), coating thickness per pass, and microstructural parameters including porosity, cracks, and interfacial defects/delamination. The study identified process gas temperature as the primary factor influencing both DE and thickness per pass. Higher gas temperature and pressure, combined with increased scanning speed, resulted in higher DE. The DE of the MA Cantor alloy powder peaked at around 14-15%, with a deposit density greater than 99% achieved at the highest process gas temperature and pressure (1000 °C and 60 bar, respectively). The average hardness of the optimal CS coating deposited using MA powder was found to be 679 ± 17 HV0.1, which is approximately 90% greater than the average hardness reported for CS coatings deposited using atomized powder.

Microstructure and Mechanical Properties of Nanocrystalline CoCrCuFeNi High-Entropy Alloy Coating Manufactured by Atmospheric Plasma Spraying

Microstructure and Mechanical Properties of Nanocrystalline CoCrCuFeNi High-Entropy Alloy Coating Manufactured by Atmospheric Plasma Spraying

Effect of Ti, Mn and Mo on the microstructure and properties of CoCrFeNi high entropy alloy coatings prepared by laser cladding

CoCrFeNi-based High Entropy Alloys (HEAs) coatings, with additions of Ti, Mn, and Mo, were synthesized using laser cladding (LC). The pure CoCrFeNi HEA had a uniform FCC structure, exhibiting the lowest hardness and wear resistance but good corrosion resistance. The Ti-added HEA had an FCC+Laves+η phase structure, showing increased hardness and wear resistance due to abrasive and mild surface fatigue wear, though with the poorest corrosion resistance. The Mn-added HEA maintained a single FCC structure with coarser grain boundaries, exhibiting lower hardness and reduced wear resistance due to adhesive, abrasive wear, and minor surface fatigue wear, but with the best corrosion resistance.The Mo-added HEA developed a eutectic structure of FCC and σ phases, achieving the highest hardness and wear resistance due to oxidative wear, but showed moderately decreased corrosion resistance. The varying microstructures significantly impacted the coatings' mechanical properties and corrosion behavior, highlighting the critical role of alloying elements in customizing LCed-HEA coatings for specific applications.

Effect of Substrate Bias on the Structure and Tribological Performance of (AlTiVCrNb)CxNy Coatings Deposited via Graphite Co-Sputtering

In the existing literature, there are few studies on the effect of deposition bias on the tribological properties of carbon-doped high-entropy alloy coatings. In order to further study the effect of the deposition bias on the properties of coatings, (AlTiVCrNb)CxNy coatings were deposited via unbalanced RF magnetron sputtering. The microstructure and tribological properties of carbon-doped high-entropy alloy ceramic coatings under different deposition biases were studied. The composition, morphology, crystal structure, and chemical morphology of each element of the coating were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The hardness, elastic modulus, friction, and wear properties of the coating were further characterized using a nanoindentation instrument, reciprocating sliding friction, a wear tester, and a white light interferometer. The coating density reached the optimal level when the deposition bias value was 90 V. The hardness and elastic modulus of the (AlTiVCrNb)CxNy coating increased first and then decreased with an increase in deposition bias, and the maximum hardness was 23.98 GPa. When the deposition bias was 90 V, the coating formed a good-quality carbon transfer film on the surface of the counterbody due to sp2 clusters during the friction and wear process. The average friction coefficient and wear rate of the (AlTiVCrNb)CxNy coating were the lowest, 0.185 and 1.6 × 10−7 mm3/N·m, respectively. The microstructure, mechanical properties, and tribological performance of the (AlTiVCrNb)CxNy coating were greatly affected by the change in deposition bias, and an (AlTiVCrNb)CxNy coating with excellent structure and friction properties could be prepared using graphite co-sputtering.

Microstructure and properties of Al/FeCoNiCrMo coatings prepared by different plasma spraying currents on carbon fiber reinforced plastic surfaces

Al/FeCoNiCrMo high-entropy alloy (HEA) coatings were prepared on the surface of carbon fiber reinforced plastic using plasma spraying technology. The microstructure of the HEA coatings was characterized under different spraying currents, and the hardness, interfacial bonding, corrosion resistance and friction and wear properties of the coatings were tested. The results showed that with the increase of the current, the unfused particles in the coatings decreased, and the coating porosity and thickness also decreased gradually; the hardness, corrosion resistance and friction and wear resistance properties increased with the increase of the current, in which the maximum hardness was 740.3 HV0.1, and the minimum self-corrosion current was 1.21 × 10−5 A·cm−2, and the minimum volumetric wear rate was 7.66 × 10−5 mm3·N−1·m−1.