Phase Composition Of Coatings Research Articles

Formation of Corrosion‐Resistant Nitride Coatings Based on Ti–Al–Cr–Fe–Ni High‐Entropy Alloy

The purpose of the work is to study the features of the phase and structure formation of coatings (Ti–Al–Cr–Fe–Ni)N formed by vacuum arc deposition and to study the influence of technological parameters of the deposition process on their corrosive properties. It is established that on the basis of the selected elements, it is possible to form a high‐entropy compound in the form of a solid solution. The structure of nitride coatings based on high‐entropy compounds formed by vacuum arc deposition is studied. It is established that the phase composition of coatings largely depends on the ratio of titanium and aluminum, which is determined by the technological parameters of deposition. An analysis of the results of the electrochemical behavior of coatings (Al,Ti,Fe,Cr,Ni)N shows that an increase in the corrosion resistance of these coatings is due to the synergistic effect of the formation of a solid substitution solution with a dense nanoscale structure and an increased relative aluminum content in them.

Phase composition, microstructure and mechanical properties of CVD Ti–B–N coatings deposited at different temperatures guided by thermodynamic calculations

TiBN coatings, as materials with broad potential applications, have received much attention in surface engineering in recent years. Within this work, the chemical vapor deposition (CVD) phase diagrams of TiBxNy coatings were calculated and the effects of deposition temperature (830–920 °C) on the microstructure, phase composition and mechanical properties of CVD TiBxNy coatings were investigated. The TiB0.61N0.84 and TiB0.61N0.81 coatings deposited at 830 and 860 °C have a particle-like surface, the TiB0.56N0.88 and TiB0.55N0.92 coatings deposited at 890 and 920 °C exhibit needle-like characteristic. XPS and TEM results indicate that TiBxNy coatings consist of nanocrystalline TiN and TiB2 embedded in amorphous TiB and BN matrix. The TiB0.61N0.84 coating exhibits the highest hardness of 40.7 GPa. The hardness of the coatings decreases as the deposition temperature increases. The presently developed approach of thermodynamic calculations and key experiments is equally valid for the efficient deposition of other CVD coatings.

Effect of WC particle size on the microstructure and tribological properties of high-speed laser cladding Ni/WC composite coatings

Ni/WC composite coatings with WC particle sizes of 30–65, 65–100, and 100–145 μm were prepared on 304 steel using high-speed laser-cladding (HSLC). The phase composition, microstructure, and wear mechanism of the composite coatings were studied. The dendrite-growth mechanism around WC with different particle sizes and the effects of WC with different particle sizes on the microhardness and tribological properties of the composite coatings were analyzed. The results demonstrated that the composite coating consisted of intermetallic compound Ni3Fe and secondary carbides W2C and (Cr, Fe)7C3. The composite coating exhibited good macroscopic morphology and uniform microstructure. The WC particle size obviously influenced the columnar and cellular dendrites in the coating. The microhardness values of the three groups of composite coatings were 419.35, 314.64, and 331.65 HV. The average friction coefficients were 0.4876, 0.5693, and 0.5439. The wear volumes were 0.001, 0.0015, and 0.002 mm3. The wear mechanisms included adhesive, abrasive, and oxidation wear mechanisms. The results verified that the WC coating with a small particle size possessed the best microhardness and tribological properties.

Microstructure, hardness, and tribological properties of CoCrFeNiX (X = Mo, Ti, W) high entropy alloy coating by red-blue composite laser cladding on copper alloy

In this study, the problem of high reflectivity of copper alloy surface to traditional infrared laser beam was overcome by red-blue composite laser cladding technology. The problem of cracks and other defects caused by the large difference in thermal expansion coefficient between copper substrate and high entropy alloy coating was overcome by electroplating Ni intermediate layer on the surface of copper alloy. A high-entropy alloy coating with tight bonding and no obvious defects was successfully prepared on the surface of copper alloy. The phase composition, microstructure evolution, hardness and tribological properties of high-entropy alloy coatings after adding different elements were studied. The experimental results show that all the CoCrFeNi coatings are FCC phase. After the addition of Mo, Ti and W elements, σ phase rich in Mo and Cr, TiCo2-type Laves phase and Fe7W6-type μ phase appeared in the high entropy alloy coating, respectively. The average microhardness of CoCrFeNiX (X = Mo, Ti, W) high entropy alloy coatings reached 730 HV0.2, 1090 HV0.2 and 378 HV0.2, respectively. The wear rates of CoCrFeNiMo, CoCrFeNiTi and CoCrFeNiW high-entropy alloy coatings were 47.17 %, 90.56 % and 22.64 % lower than those of CoCrFeNi coating, respectively. The wear scars were analyzed by SEM and EDS, and the friction and wear behavior mechanism of CoCrFeNiX (X = Mo, Ti, W) high-entropy alloy coating was investigated. It is mainly composed of abrasive wear, adhesive wear and oxidation wear. The research results provide practical guidance for the preparation of high-entropy alloy coatings on copper surface, and lay a theoretical foundation for laser cladding such high-entropy alloy materials and substrate materials.

Microstructure and mechanical property regulation of plasma-sprayed high-entropy (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 thick coatings

The effect of critical plasma spraying parameters (CPSPs) on phase composition, microstructure and mechanical property of (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 thick coatings was investigated. After coating deposition, the phase structure of (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 was transformed from pyrochlore to fluorite in the coating. When the CPSP value increased from 0.83kW/Lpm to 1.17kW/Lpm, the porosity of as-deposited coating was decreased from (16.46 ± 0.65)% to (6.94 ± 0.44)%. As a result, the elastic modulus of the coating was improved from (59.34 ± 2.39) GPa to (79.19 ± 4.78) GPa, and the corresponding micro-hardness was also increased from (2.59 ± 0.30) GPa to (3.39 ± 0.37) GPa. Consequently, the fracture toughness of as-deposited coating was decreased with the increasing CPSP value, while the corresponding residual stress was obtained to be compressive stress and it increased from -(43.00 ± 1.96) MPa to -(70.42 ± 3.89) MPa, indicating that the lower CPSP value was beneficial to reducing the residual compressive stress, which might be in favor of enhancing thermal shock resistance of coating.

In-situ synthesis and oxidation behaviors of Ti-xAl coatings by high-frequency induction heated combustion

Ti-xAl coatings (x=25, 33.3, 50, 66.7, and 75 at%) were fabricated in situ using high-frequency induction heating synthesis (HFIHCS). The process parameters for preparing Ti-Al coatings via HFIHCS were orthogonally optimized employing the finite element method. The effect of the aluminum content on the microstructures and phase compositions of Ti-Al coatings fabricated by HFIHCS, as well as their oxidation behaviors at 900℃ for 100 h was investigated. The results showed that the distribution of interfacial temperature difference was influenced by induced current (62.11%), relative density of compact (9.86%), and indenter material (28.03%). The minimum interfacial temperature difference was achieved with an induced current of 300 A, a graphite indenter material, and a compact density of 82.9%. The Ti-xAl coatings exhibited a core (Ti)-shell (TixAly) ring structure. The rise in aluminum content in the Ti-xAl coatings led to a gradual reduction in the titanium-rich phase, accompanied by a progressive increase in the aluminum-rich phase and the interface thickness of zones Ⅰ and Ⅱ. The porosities of Ti-xAl coatings containing over 50 at% aluminum exhibited an order of magnitude higher than those of Ti-xAl coatings with 50% aluminum or lower. The mechanisms of reaction, pore-forming, and interfacial diffusion for Ti-xAl coatings were predominantly controlled by dissolution-precipitation, thermal expansion of intrinsic pores within the cold-pressed compact and voids formed after molten aluminum flow, and liquid-solid co-diffusion, respectively. The increase in aluminum content in the Ti-xAl coatings led to in a gradual decrease in its oxidative weight gain, a shift in the oxidation kinetics from a linear-parabolic to a parabolic law, and an enhancement in preservation of internal core-shell characteristics and the likelihood of forming a protective layer of thin Al2O3. The oxidation behaviors of Ti-xAl coatings with a core-shell structure were co-controlled by the aluminum content and the porosity affected by the aluminum content.

Effect of laser remelting on the microstructure and corrosion behavior of high-velocity arc-sprayed FeNiCrBSiNbW amorphous coating

Fe-based amorphous coating was produced using high-velocity arc-spraying (HVAS), and then laser remelting (LR) technology was used to treat the as-sprayed coatings (ASC) to prepare the laser remelted coatings (LRC). The morphology, phase composition, microhardness, porosity, and corrosion property of the Fe-based amorphous coatings before and after LR were investigated. The outcomes demonstrated that the internal defects of the ASC were eliminated and the porosity was significantly reduced after LR, which was significant in dramatically enhancing corrosion resistance. After the LR procedure, the ASC's free corrosion potential (Ecorr) in 3.5 wt% NaCl solution increased, and the corrosion current density (Icorr) almost reduced by a factor of ten. Therefore, LR helped to strengthen the corrosion characteristics of Fe-based amorphous coating and improve its microstructure.

The Structure of Boride Diffusion Coatings Produced on Selected Grades of Structural Steels

In the article the microstructure and phase composition of boride coatings deposited on selected structural steels were investigated. The boride coatings were produced using pack cementation method using commercial EKABOR-2 mixture containing of 50 wt. % of new and 50 wt. % of used powder. Boride coatings were deposited on alloyed structural steels grades (PN/EN 10084 standard): 16MnCr5, 18CrNiMo7-6, 41CrAlMo7 42CrMo4. Cylindrical samples with a diameter of 30 mm and a height of 30 mm were boronized in powder at 1000°C for 2, 4 and 6 hours in an argon atmosphere. The process was carried out in an industrial CVD Bernex BPX 325S device. The microstructure was analyzed using scanning electron microscope Phenom XL equipped with EDS spectrometer. The XRD phase analysis was conducted using XTRa diffractometer (ARL). The thickness as well as phase composition was analyzed on coatings formed on each grades of steels. The most of obtained boride coatings were characterized by single-phase structure (Fe2B). The formation of brittle FeB phase was detected only on 16MnCr5 steel grades steels.

Influence of spraying power on microstructure, phase composition and nanomechanical properties of plasma-sprayed nanostructured Yb-silicate environmental barrier coatings

Currently, achieving high stability for environmental barrier coatings (EBCs) in service at higher operational temperatures (>1400 °C) remains a challenging issue. In our previous work, a nanostructured Yb-silicate coating was successfully fabricated, which could be a promising EBC candidate for CMC (Ceramics Matrix Composites) components protection at higher temperatures. However, there have been limited reports on the relationship between mechanical properties and spraying power for producing a nanostructured Yb-silicate coating. Therefore, this study delves into the microstructure, phase composition, and nanomechanical properties of nanostructured Yb-silicate coatings before and after heat treatment at different spraying powers. The results indicate that, due to the intricate interplay of microstructural and phase composition evolution, noticeable disparities in nanomechanical properties were observed in nanostructured Yb-silicate coatings before and after heat treatment. It is noted that the as-sprayed coating at 36 kW exhibits comparable nanomechanical properties to 45.5 kW, whereas the heat-treated coating demonstrates higher nanohardness and elastic modulus at 36 kW but greater damage tolerance at 45.5 kW. These findings offer a preliminary guidance for optimizing process parameters in nanostructured Yb-silicate coating's preparation, and laying the foundation for further researches.

Microstructure and Mechanical Properties of TiC/WC-Reinforced AlCoCrFeNi High-Entropy Alloys Prepared by Laser Cladding

By employing the technology of laser cladding, AlCoCrFeNi–TiC20−x/WCx high-entropy alloy coatings (where x = 0, 5, 10, 15, and 20 is the mass fraction) were fabricated on 316L stainless steel (316Lss). The effects of changes in different mass fractions on the morphology, phase composition, microstructure, microhardness, and corrosion resistance of the composite coatings were studied. This demonstrates that the addition of TiC and WC powder produces an FCC phase in the original BCC phase, the morphology and size of the coatings from top to bottom undergo some changes with x, and the grain size evolution follows a cooling rate law. The evolution of microhardness and corrosion resistance of the coatings exhibit a trend of increasing first and then decreasing with an increase in x. The coatings exhibited their best microhardness and corrosion resistance when x = 15, and their corrosion resistance and microhardness were much better than those of the substrate.

Effect of WC on the microstructure and mechanical properties of laser-clad AlCoCrFeNi2.1 eutectic high-entropy alloy composite coatings

AlCoCrFeNi2.1/WC eutectic high-entropy alloy composite coatings were prepared on a 316 L stainless steel substrate via the laser cladding method. The effects of the WC content on the phase composition, microstructure, and mechanical properties of the composite coatings were investigated. The results revealed that the laser-clad AlCoCrFeNi2.1/WC eutectic high-entropy alloy composite coating mainly consisted of FCC and BCC phases. As the WC content increased from 0 wt% to 30 % wt%, the Cr7C3 and Cr21W2C6 phases were gradually precipitated from the composite coating. Consequently, the microhardness of the composite coating increased from 318.6 to 572.3 HV1.0. The strengthening mechanism of composite coatings mainly comprised solid solution strengthening, second-phase strengthening, and fine-grain strengthening. Additionally, the high dislocation density, caused by rapid condensation during the laser cladding process, contributed to the improvement in the coating hardness. Wear experiments revealed a significant improvement in the wear resistance of the composite coating with increasing WC content. The composite coating with 30 wt% WC exhibited the highest hardness and wear resistance with an average friction coefficient of 0.535, as well as a wear rate and wear volume loss of 4.4 × 10−7 mm3N−1 mm−1 and 5.44 mm3, respectively.

Improving abrasion resistance of low temperature enamel (LTE) coating by alumina addition

Low temperature enamel (LTE) coating has advantages in material durability, hardness, corrosion resistance, and high-temperature tolerance, but shows unsatisfying abrasion resistance due to its brittle nature. Here, alumina was added to the LTE coating with contents of 0, 5, and 10 wt%. The thermal stability of alumina in the LTE matrix and the microstructure, phase composition, microhardness, impact resistance, adhesion strength, abrasion resistance, and corrosion protection properties of different LTE coatings were investigated. Results indicated that alumina had high thermal and chemical stabilities in the LTE matrix without affecting the pore structure of the coating. As an abrasion-resistant filler, alumina increased the hardness and impact resistance of LTE coatings while reducing adhesion strength. In the abrasion test, alumina showed an advantage in delaying the formation and expansion of cracks, and the alumina-enhanced LTE coating demonstrated a 70 % reduction in mass and thickness losses when compared to pure LTE coating. In particular, all LTE coatings survived 8000 cycles of abrasion without significant degradation in corrosion protection. The findings of this study confirmed the feasibility of alumina as an abrasion-resistant filler and provided a modified LTE coating for coupled corrosion and abrasion conditions.

Zinc–rich inorganic silicate anticorrosive coating incorporating muscovite for steel bars in sand–based autoclaved aerated concrete

Corrosion is a thorny problem when steel reinforcement in sand–based autoclaved aerated concrete (SAAC) is in use. In this study, potassium silicate was used as the base material and muscovite and zinc powder were added as fillers to improve the coating properties. In addition to physical and mechanical properties, electrochemical tests including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were performed on the coatings. The phase composition, chemical composition and morphological differences of different coatings were also characterized. The results showed that zinc powder increased the density of the muscovite–potassium silicate coating and significantly improved the corrosion resistance and mechanical properties of the coatings. The prepared coatings exhibited stable qualities with no heat absorption and release before 365 °C. The adhesive strength and impact resistance of the coatings were as high as 2.43 MPa and 50 kg cm, respectively. The electrochemical test results showed that the coating resistance (Rc), charge-transfer resistance (Rct), and polarization resistance (Rp) of the C-5.5–55–40 coating were 23578, 3.542 × 105, and 2.911 × 105 Ω cm2, respectively, which exhibited the optimal corrosion resistance.

Microstructure, phase composition and wear properties of iron-based gradient coatings by laser cladding on 65Mn steel

Iron-based coatings with high wear resistance were prepared on a 65Mn substrate using a laser cladding technique. The coatings were characterized and compared with the substrate in terms of microstructure, phase composition, hardness distribution and friction-wear properties. The coatings had a gradient microstructure consisting of a working layer and a transition layer with different compositions. The working layer contained (Cr, Fe)7C3 carbides as the hard phase, which improved the hardness and wear resistance of the coatings. The transition layer had a higher soft phase amount due to the higher Ni content, which enhanced the bonding strength between the coating and the substrate. The coatings showed a uniform and dense surface morphology, free of cracks and pores, and a fine and uniform grain size. The average hardness of the coatings was 721 HV1, which is more than three times that of the substrate. The friction coefficient and wear loss of the coatings were 0.42 and 0.0018 mg/m, respectively, lower than those of the substrate (0.48 and 0.036 mg/m). The coatings demonstrated excellent wear resistance and durability in soil tank tests, exhibiting an 81.15 % reduction in mass loss when utilized on rotary tiller blades. The results present an effective method for surface modification of agricultural machinery components and provide valuable insights for the further development of unique gradient coatings.

Mechanistic analysis of improving the corrosion performance of MAO coatings on Ti-6Al-4V alloys by annealing

Titanium and its alloys find extensive application within the realms of dentistry and orthopedics due to their remarkable chemical stability. Nevertheless, they are still susceptible to corrosion in harsh environments. Micro-arc oxidation (MAO) emerges as a potent methodology for enhancing the corrosion resistance of titanium and its alloys, achieved through the generation of a ceramic stratum atop the material's surface. The corrosion resistance of MAO coatings in clinical applications is closely related to their microstructure. This manuscript systematically explores the effect of annealing temperature on the phase composition and microstructure of MAO coatings. Furthermore, the evolution of the surface properties and the crystal structure of coatings is meticulously discussed and illustrated. The results show that the corrosion resistance of coatings exhibits an ascending trajectory followed by a subsequent decline, coinciding with the augmentation of the annealing temperature. This behavior can be attributed to the structural evolution of coatings caused by the gradual increase of the annealing temperature. At the optimum temperature (400 °C), the annealing treatment leads to the crystallization of the coating as well as to a decrease in the surface porosity, resulting in the formation of a compact and continuous multilayer microstructure. The decrease in porosity can be attributed to the diffusion-reaction of oxygen from the air with titanium from the discharge channel (titanium oxide), resulting in the formation of TiO2 particles that effectively fill the pores. The decrease in corrosion resistance of the coatings after annealing at 800 °C is due to the phase transition of TiO2 which leads to the expansion of cracks inherent in the oxide layer to form A-H cracks. Therefore, this study shows that the microstructure of MAO coatings can be adjusted by post annealing treatment (400 °C) to obtain a desirable oxide layer with appropriate porosity, crystallinity and chemical composition, thus improving its corrosion resistance.

Photoactive TiO2 ceramic coatings obtained by laser-assisted plasma electrolytic oxidation on commercial pure titanium

To address the challenges of controlling the morphology and crystalline phase composition of photoactive TiO2 ceramic coatings produced by existing plasma electrolytic oxidation (PEO) technology, a novel laser-assisted PEO method is proposed in this study. The analysis has revealed that the TiO2 coatings prepared by the laser-assisted PEO method had a more intricate 3D multi-porosity architecture. Furthermore, the ratio of TiO2 crystalline phases (anatase to rutile) in the coating can be controlled by adjusting the laser energy during the laser-assisted irradiation process. The fundamental reason for the change in the morphology and composition of the crystalline phases of the coatings is the induction and enhancement of the plasma discharge by laser-assisted irradiation. The photoelectrochemical behavior of the samples was evaluated by employing linear sweep voltammetry under continuous UV irradiation, and the photoresponse current density was measured under intermittent UV irradiation. The laser-assisted PEO coatings prepared with 80 W laser energy under laser-assisted irradiation exhibited the most favorable photoelectrochemical activity. Furthermore, further analysis showed that the enhanced photoelectrochemical activity of the photoactive titanium dioxide coatings was essentially due to a larger specific surface area, lower impedance, higher wettability, and a more suitable crystalline phase ratio.

Oxidation behaviors of electrodeposited MoSi2 coating in a wide temperature range from 773 K to 1673 K

In this study, a MoSi2 coating was prepared on the surface of a molybdenum (Mo) substrate using the molten salt electrodeposition method, and the oxidation behavior of the coating over a wide temperature range from 773 K to 1673 K was studied in detail. The phase composition, surface and cross-sectional morphologies of the MoSi2 coatings after oxidation at various temperatures were characterized, and the evolution of the phase and microstructure were analyzed to elucidate the oxidation mechanism. The experimental results showed that the MoSi2 coating exhibited excellent oxidation resistance at lower temperatures (773 K) and did not experience the pesting phenomenon. When exposed to medium and high temperatures, a continuous and dense SiO2 layer was formed on the surface of the MoSi2 coating, which effectively prevented further oxidation inside the coating, thereby protecting the Mo substrate. Meanwhile, at higher temperatures, especially at 1473 K and 1673 K, the solid-phase diffusion of Si towards the substrate gradually transformed the MoSi2 into Mo5Si3 with a lower Si content. Notably, the thickness of the Mo5Si3 layer that was distributed between the original MoSi2 coating and the Mo substrate increased with the oxidation time and temperature. At 1673 K, a Mo3Si layer with a low Si content was formed beneath the Mo5Si3 layer. Thus, the diffusion of Si was an important factor restricting the service life of MoSi2 coating.

Microstructure and properties analysis of AlCoCrFeNi high-entropy alloy/iron-based amorphous composite coatings prepared by laser cladding

AlCoCrFeNi HEA coatings with iron-based amorphous powder mass fractions of 0%, 3%, 6%, 9%, 12%, and 15% were fabricated on 316L stainless steel by laser cladding technique. The microstructure, phase composition, microhardness, and corrosion resistance of the composite coatings were analyzed by various characterization techniques. The results showed that the addition of iron-based amorphous powder has a significant influence on the crystal structure, phase, microhardness and corrosion resistance of the composite coatings, but the presence of excessively high of iron-based amorphous powder will disorder the crystal structure, which reduces the microhardness of the composite coatings.

Effect of electrochemical parameters on wear and tribocorrosion capabilities of the PEO coatings generated through pulsed waveforms on AZ91 magnesium alloy

In this study, PEO coatings were produced on AZ91 Mg alloy using pulsed waveforms at different electrical parameters such as type (unipolar and bipolar), cathodic duty cycle (20 and 40 %), and voltage amplitude (350 and 400 V) to assess wear and tribocorrosion resistance. The coating bath contained NaAl2O4 and NaF. The coating phase composition, microstructure, and chemical composition of the coatings were evaluated using GXRD, SEM, and EDS. Dry wear behavior was studied using the reciprocating ball-on-flat device, while tribocorrosion behavior was evaluated by immersing the coated specimens in 3.5 wt% NaCl solution and reading the OCP before, during, and after sliding. The worn area in both cases was also examined. The results showed that the bipolar waveform with the higher cathodic duty cycle (40 %) provided the best tribocorrosion and wear performance by forming MgF2 (as a corrosion-resistant phase) and MgAl2O4 (as a hard phase). At all three waveforms, the higher coating voltage (i.e. 400 V) enhanced the wear and tribocorrosion resistance by forming thicker coatings with higher amounts of MgF2 and MgAl2O4 phases.

Effect of Heat Treatment on the Phase Composition of Copper-Zinc Coating on Steels

Effect of Heat Treatment on the Phase Composition of Copper-Zinc Coating on Steels