Amorphous Coatings Research Articles

Effect of Laser Energy Density on Amorphous Phase Content and Properties of Fe-Based Amorphous Coatings

Effect of Laser Energy Density on Amorphous Phase Content and Properties of Fe-Based Amorphous Coatings

Corrosion behaviour of HVOF developed Mo-based high entropy alloy coating and selected hard coatings for high temperature geothermal applications

The corrosion behavior of High Entropy Alloy (HEA), wear-resistant cermets, self-fluxing Ni alloy, and Fe-based amorphous alloy coatings were investigated in simulated alkaline high-temperature geothermal environments with/without H2S and CO2 gases for geothermal applications. Phase density of the corrosive fluid (liquid/vapor) influenced the corrosion behavior in the test environments. The NiCrSiBFe self-fluxing coating formed a continuous corrosion surface film while the FeCrMoWMnBCSi amorphous coating was prone to localized corrosion in the liquid phase. The cermet coatings had pores and cracks that led to localized penetration while the CoCrFeNiMo0.85 HEA showed the highest corrosion resistance in all test environments with no localized corrosion damage.

Microstructural, mechanical and high-temperature tribological performance of Fe-based fully amorphous and amorphous/crystalline coatings

In this research, fully amorphous and amorphous/crystalline (A/C) Fe-based coatings were explored for high-temperature tribological applications. The commercially available gas atomized feedstocks were sprayed using high velocity oxygen fuel (HVOF) processes. The microstructural, mechanical and tribological behaviour of the coatings were investigated and compared. The fully amorphous Fe-based amorphous coating exhibited higher wear resistance at 600 °C than room temperature (RT) with high thermal stability and performed superior to A/C coatings at both temperature conditions. Detailed analysis of worn surfaces demonstrated that fully amorphous coatings were dominated by abrasive wear and oxidative wear at RT and oxidative and adhesive wear at 600 °C, whereas A/C coating suffered abrasive, surface fatigue wear and minor oxidation at both RT and 600 °C. A thick oxide glaze layer formed onto the worn surface of fully amorphous coatings, which enhanced the high-temperature mechanical properties and prevented severe wear loss. The Fe-based amorphous coating exhibited superior wear resistance and retained its phase structure, which established it as a potential high-temperature protective coating for tribological applications.

Microstructural evolution and properties of He-charged a-Si coatings prepared by magnetron sputtering

The introduction of porosity in nanomaterials via magnetron sputtering in helium atmospheres is an interesting strategy for the design of functional materials. Amorphous silicon coatings, with high concentration of He incorporated in the form of overpressurized nano-bubbles, present modified optical properties in comparison with dense coatings of similar composition.In this work, annealing process in He atmosphere from 300 °C up to 1200 °C is performed to evaluate stability after the release of He from the a-Si:He coatings (thickness ∼1700 nm) and to favor matrix crystallization and defect evolution. The work is focused on these effects on the silicon film and its properties. The composition and microstructural evolution of the coatings annealed to temperatures as high as 1200° were investigated by electron microscopy and X-Ray diffraction. Annealing effects on the optical properties and bandgap of the silicon coatings were evaluated by ellipsometry and UV–Vis spectrometry. Helium release from the coating, densification, defects evolution and ordering due to crystallization have a small effect on the refractive index, but cause a significant change in the material band gap from 1.37 eV to 1.80 eV.

The Effect of Ni Interlayer Formation Plating Bath on the Suppression of Oxidation of Ag-Coated Cu Flakes

To suppress Ag dewetting from around 200 oC in Ag-coated Cu (Cu@Ag) flakes, Ag and Ni-coated Cu (Cu@Ni@Ag) flakes were fabricated by successive Ni and Ag electroless plating. The Ni bath type was an important consideration to induce differences in the Ag dewetting and resultant Cu oxidation. An acid Ni bath contained succinic acid as a complexing agent and sodium hypophosphite as a reductant, and an alkaline Ni bath contained sodium citrate as a complexing agent and sodium hydroxide as a pH adjuster as well as sodium hypophosphite. A hydrazine-based Ni bath contained sodium citrate, sodium hydroxide, and hydrazine hydrate as a reductant. The acid Ni bath provided amorphous coatings with a P content of approximately 10 wt%. The Cu@Ni@Ag flakes started the Ag dewetting and Cu oxidation at 350 oC, together with the formation of the Ni3P phase. Meanwhile, the alkaline Ni bath created Ni-5 wt% P amorphous Ni coatings, which transformed into a crystalline phase after heating at 350 oC. The Ag shell was dewetted at 450 oC, which caused oxidation of the flakes. Finally, the hydrazine-based Ni bath formed crystalline coatings without P, which induced rapid mixing with the core Cu. The Ag shells on the mixed Cu-Ni alloy showed repressed dewetting behavior, and thus the dewetting and oxidation temperature was the highest, such as 500 oC. Enhancing the high oxidation resistance at approximately 300 oC will enable the use of Cu@Ni@Ag flakes as a low-cost filler material in conductive pastes, especially for long-time or high-temperature curing.

Superhydrophobic Fe-based amorphous alloy coatings with excellent anti-fouling and anti-corrosion properties by picosecond laser texturing

Producing superhydrophobic surfaces on the amorphous alloy coatings with excellent anti-corrosion and anti-fouling properties offers a promising strategy to broaden the applications of amorphous alloys in marine fields. In this work, the superhydrophobic surfaces on the Fe-based amorphous alloy coatings with micro-nano hierarchical structures were fabricated using picosecond pulsed laser texturing (LT) and surface chemical modification. The fabricated superhydrophobic coating surfaces have achieved a maximum contact angle of 166.5°and a minimum sliding angle of 3.6°. Additionally, these produced coatings also demonstrate outstanding self-cleaning and anti-fouling properties for preventing surface contamination. The superhydrophobicity originated from the formation of micro-nano hierarchical structures and the grafting of organic compounds with low surface free energy on the LT fabricated surfaces. The changes in wettability were attributed to the differences in the solid–liquid interfacial area fractions. The electrochemistry tests revealed that the corrosion resistance of the produced coatings with superhydrophobic surfaces had improved considerably compared with the as-sprayed amorphous alloy coatings, which could broaden the functional applications of the Fe-based amorphous alloy coatings.

Room temperature nanoindentation creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings prepared by HVAF

The present study aimed to explore the creep behavior of CoNiCrMo-based high entropy amorphous alloy coatings at room temperature using nanoindentation creep experiments. The coatings were subjected to different loading rates to assess their performance. The findings indicate that the high entropy effect of the (Co0.33Ni0.33Cr0.23Mo0.1)80-xNbx(B0.7Si0.3)20 (x = 0, 2 and 4 at. %) high entropy amorphous alloy coatings has a notable impact on the creep resistance and facilitates a uniform plastic deformation during creep. The shear transition zone (STZ) size and the free volume content during creep deformation exhibit an increase in response to the concentration of Nb. This phenomenon can be attributed to the elevated atomic packing density and the hindered movement of atoms resulting from the incorporation of Nb. Nb content has a favorable impact on the creep stress index, increasing creep stress. Also, the high concentration of Nb is found to mitigate the propensity of the stress exponent to drop with increasing loading rates. The high entropy effect of the as-sprayed coatings promotes high creep resistance and homogenous creep deformation.

Osteogenic activity of a micro/nano hierarchical nano-hydroxyapatite coating on zirconium alloy

Micro/nano hierarchical structures and nano-sized hydroxyapatite (nHA) have been proven to play a critical role in promoting osseointegration. However, still, it is a challenge to prepare tightly adherent nHA coatings with micro/nano hierarchical structure, and the correlation between the physicochemical properties of hydroxyapatite (HA) and osteoblasts (OBs) activity at different stages is unclear yet. In this study, the grain refinement of large-sized HA generated by traditional microarc oxidation-hydrothermal treatment was achieved through a simple method of adding Ca/P (Ca2+ and PO43−) to hydrothermal reaction, and micro/nano hierarchical nHA coatings with different crystallinities and grain sizes were prepared on Zr16Nb12Ti alloy. Further, the OBs responses on these coatings were investigated in proliferation and differentiation stages, respectively. It was found that small-sized HA particles provide more integrin-binding sites, which are important for the adhesion and proliferation stages of OBs. The high ion release resulting from the low crystallinity of HA is a crucial condition for promoting OBs differentiation. However, amorphous HA coatings with excessively low crystallinity exhibit poor osteogenic activity due to their inferior cell adhesion activity. Finally, a micro/nano hierarchical nHA coating with appropriate crystallinity was prepared through a simple method, demonstrating excellent osteogenic activity, and providing new strategies for biomimetic coatings research.

High-speed impact behavior of cold-sprayed Fe-based amorphous particle on Mg alloy substrate

Amorphous coatings offer substantial enhancements to the surface properties of Mg alloys, particularly concerning wear and corrosion resistance. Cold spray, as a high-speed impact process conducted at low temperatures, demonstrates excellent solid-state forming capabilities for preparing amorphous coatings. However, the excellent properties exhibited by amorphous coatings require comprehensive research on the microstructure evolution of the particle-substrate interface. The results revealed varying degrees of crystallization in the amorphous particle, characterized by obvious crystallization near the particle-substrate interface, where the temperature rise exceeded the crystallization temperature, in contrast to relatively lower crystallization occurring inside the particle. Meanwhile, the high-speed impact led to the formation of a grain-refined layer in the substrate, exhibiting an approximate width of 500 nm, and featuring localized regions of amorphisation. An atomic bonding was achieved in the interfacial area of the particle-substrate where the mixed zone had a width of 40 nm.

CoxCrFeNiTi High-Entropy Alloys Prepared via Mechanical Alloying and Spark Plasma Sintering for Magnetron Sputtering Coatings.

The main objective of this study was to develop a high-entropy alloy (HEA) derived from the CoxCrFeNiTi HEA system (x = 0.5, 1) for protective coatings using the magnetron sputtering method. In order to produce the high-entropy alloy targets required for the magnetron sputtering process, mechanically alloyed metallic powders were consolidated via spark plasma sintering (SPS). The microstructural analysis results of the HEA mixture presented morphology changes after 30 h of alloying, with the particles presenting uniform polygonal shapes and dimensions. Subsequently, 316L stainless steel (SS) specimens were coated via magnetron sputtering, comparing their composition with that of the sputtering targets used for deposition to establish stoichiometry. Microstructural analyses of the SPSed HEAs revealed no defects and indicated a uniform elemental distribution across the surface. Furthermore, the CoCrFeNiTi equiatomic alloy exhibited a nearly stoichiometric composition, both in the coating and the sputtering target. The XRD analysis results indicated that amorphous coatings were obtained for both Co0.5CrFeNiTi and the CoCrFeNiTi HEA, and nanoindentation tests indicated that the CoCrFeNiTi HEA coating presented a hardness of 596 ± 22 HV, compared to the 570 ± 19 HV measured for Co0.5CrFeNiTi, suggesting an improved wear resistance.

High Hardness, Excellent Hydrophobicity, and Favorable Corrosion Resistance of Plasma-Sprayed FeCrMoSi Amorphous Coatings on 304 Stainless Steel.

The FeCrMoSi amorphous coatings were fabricated on the surface of a 304 stainless steel (SS) base material using atmospheric plasma spraying. A comprehensive investigation was carried out to evaluate the structure, morphology, adhesion to base material, hardness, hydrophobicity, interfacial contact resistance, and corrosion resistance of the coatings. The results show a remarkable hardness of 1180.1 HV, a strong bond strength of up to 64.3 N/mm2, and excellent hydrophobicity with a water contact angle reaching 141.2°. Additionally, in an acidic environment with fluoride ions (0.5 M H2SO4 + 2 ppm HF, 80 °C), the FeCrMoSi amorphous coating demonstrated superior corrosion resistance compared with 304 SS while maintaining similar electroconductibility. Detailed analysis of the structural characteristics and corrosion resistance of FeCrMoSi amorphous coatings provided valuable insights into their mechanics. These promising results signify a bright future for FeCrMoSi amorphous coatings in various industrial sectors, including transportation, petroleum, and electric power industries.

Effect of Sn on corrosion resistance of Ti-Cu-Ni amorphous coating

Ti50Cu35-XNi15SnX (X = 5,6,7, wt%) Ti-based amorphous composite coatings were prepared on TA1 by atmospheric plasma spraying. The phase and microstructure were analysed by X-ray diffractometerand scanning electron microscope. The obtained cross-section image of the titanium-based amorphous composite coating confirmed the successful preparation of the amorphous coating. The phase analysis results indicated that an increase in Sn content resulted in a decrease in the amorphous content of the coating. The electrochemical results revealed a significant improvement in the corrosion resistance of the coating compared to the TA1 substrate, consequently enhancing the service life of the electronic material. When the Sn content was 5 wt%, the minimum current density of the coating reached 8.62 × 10-6 A/cm2, and the corrosion rate was 16 times lower than that of the TA1 substrate. As the Sn content increased, the current density of the coating increased from 8.62 × 10-6 A/cm2 to 5.08 × 10-5 A/cm2. Overall, the corrosion resistance of the coating exhibited a downward trend. This observation could be attributed to the decrease in amorphous content caused by the higher Sn content, resulting in a reduction in the corrosion resistance of the coating.

Histological and mechanical properties of laser-melted carbon nanotube-toughened Fe-based amorphous coatings

Abstract Laser melting technology is a new surface fabrication technique, and using laser beams to improve the mechanical properties of iron-based amorphous prepared by laser melting has become a hot topic in current materials research. Firstly, nickel-plated carbon nanotubes were used to improve the toughness of iron-based amorphous coatings, and nickel-plated carbon nanotubes were used to prepare iron-based amorphous composite fusion cladding layers. Then, the iron-based amorphous has good strength, strong wear resistance and corrosion resistance and is a good surface modification material. Finally, considering that the preparation of iron-based amorphous coating by laser melting technology can meet the preparation requirements of fast cooling of iron-based amorphous, the organization and mechanical properties of the iron-based amorphous coating are studied and analyzed by using laser melting technology. The results show that the toughness of the amorphous-1.00 wt% nickel-plated carbon nanotube composite clad layer is 7.67 MPa-m which is 33.4% higher than the amorphous clad layer. The composite clad layer with the addition of carbon nanotubes showed a significant increase in toughness without a significant decrease in hardness, and the prepared nickel-plated carbon nanotube/amorphous composite clad layer had better overall mechanical properties. This study improves the mechanical properties of iron-based amorphous coatings, which is important to improve the problems of decreasing service life and stability of equipment and components caused by corrosion and wear.

Adding high entropy alloys to improve microstructure and properties of laser cladding Fe-based amorphous coatings

In this study, the A-H coatings (abbreviation for Fe-based amorphous and high-entropy alloy), which is consist of Fe-based amorphous powders and adding trace high-entropy alloy (HEA) powders, were prepared via laser cladding technique. The microstructure and properties of the A-H coatings and the Fe-based amorphous coatings were investigated in detail using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). It is found that the number of pores, cracks and dendrites of the A-H coatings is reduced due to the formation of Fe3Ni embedded in amorphous phase compared with Fe-based amorphous coatings. The average microhardness of the A-H coatings is about 1519.2±35.7 HV0.2, which is improved by 38.7%. The wear rate of the A-H coatings is found to decrease by 45.8%. Furthermore, A-H coatings exhibited exceptional corrosion resistance, with a polarization resistance that increased by 31.7%. The addition of HEA is a potential strategy to improve microstructure and properties of Fe-based amorphous coatings.

One-step fabrication of amorphous/ITO-CNTs coating by plasma electrolytic oxidation with particle addition for excellent wear resistance

As moving machine parts, aluminum alloys suffer from poor wear resistance, however, the combination of amorphous materials and anti-friction lubricant phases has rarely been investigated to improve tribological performance. The amorphous coatings were fabricated by one-step plasma electrolytic oxidation (PEO) with ITO and CNTs addition, of which CNTs were used as lubricant additives to enhance the anti-friction properties of aluminum alloy. It is found that the amorphous phases in the coatings increase with ITO concentration in the electrolyte. As well as, when the concentration of ITO in the electrolyte reaches 40 g/L, XRD cannot detect Al2O3 phase, but only ITO and amorphous phase. The formation of the amorphous coating is due to the fact that In3+ can be used as a network modifier to improve the glass-forming ability of molten oxides and the rapid cooling after discharge. Further, the amorphous coating exhibits a higher hardness (1472 HV0.5) compared to single Al2O3 coatings (267 HV0.5) and its main wear mechanism is adhesive wear with a high friction coefficient (∼0.68). In contrast, with the incorporation of CNTs, the amorphous coating exhibits slight abrasive wear after 6000 sliding cycles under dry friction conditions, with a stable frictional coefficient of around 0.14. Of which, the amorphous coating (1704 HV0.5) serves as a load-bearing and CNT acts as a lubricant phase during friction and wear. Hence, through the synergistic effect of the CNTs additive and the amorphous coating, the tribological properties of aluminum alloy are significantly improved, with a low friction coefficient and shallow wear trace.

Chemical Etching, Thermally Driven Combination Strategy to Fabricate Superhydrophobic Fe-Based Amorphous Coatings with Excellent Anticorrosion Property: Based on Hydroxylation Effect.

Fe-based amorphous coatings are ideal materials for surface protection due to their outstanding mechanical properties and corrosion resistance. However, coating defects are inevitably formed during the preparation of coatings by thermal spray technology, which seriously affects the corrosion performance. Inspired by bionics, conceiving superhydrophobic surfaces with liquid barrier properties has become a new idea for the corrosion protection of metal surfaces. In this work, based on surface hydroxylation, we designed a superhydrophobic Fe-based amorphous coating with corrosion resistance by chemical etching combined with a thermally driven preparation strategy. The obtained superhydrophobic coatings exhibit liquid repellency (contact angle >150°) and excellent corrosion resistance (corrosion current density and passive current density reduced by 3 orders of magnitude). The results revealed that the superhydrophobic behavior stems from the construction of hydroxyl-induced surface micro-/nanomultilevel aggregates (cluster structures). The hydrophobic agent layer deposited on the surface of cluster aggregates and the nanoparticle elements that constitute the clusters dominate the corrosion resistance of the coating. This work provides an effective guide to the design of high-corrosion-resistant Fe-based amorphous alloy coatings and promotes their engineering applications.

Photoactive TiO2-V2O5-WO3 film composites immobilized in titanium phosphate matrix by plasma electrolytic oxidation

V-, W-containing oxide-phosphate layers on titanium were obtained by plasma electrolytic oxidation (PEO) for 5 min at anode current density i = 0.08 A/cm2 in electrolytes containing 0.05 mol/L Na6P6O18 and 0.1 mol/L (Na2WO4 + NaVO3). The effect of replacing vanadate with tungstate (NaVO3:Na2WO4 = 0:1, 1:3, 1:1, 3:1, and 1:0) was studied on voltage–time responses, PEO coatings surface morphology, composition, optical and photocatalytic properties. The coatings were investigated by X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray microanalysis, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. Under experimental conditions, amorphous coatings with a thickness of 18–27 μm and a surface porosity of 1.5–3.6% were formed. Results show that vanadium (up to 10.5 at. %) and tungsten (up to 5.2 at. %) are incorporated into surface layers in proportion to their concentrations in electrolyte. The main mechanism for the incorporation of V and W into coatings is assumed to be thermolysis of vanadungstophosphate heteropolyoxoanions, while high concentrations of polyphosphate species contribute to the amorphization of coatings and the formation of a titanium phosphate matrix. The band gap of V-containing composites decreases from 2.22 to 1.97 eV as tungsten replaces vanadium. For W-containing composites (V-free ones), the band gap is 3.19 eV. All formed coatings exhibit photocatalytic activity in the degradation of methyl orange (10 mg/LMO, 10 mmol/L H2O2) in a neutral medium (pH 6.8) under visible and UV irradiation. The gradual substitution of vanadium for tungsten in the coatings leads to a decrease in MO degradation (from 87 to 50% and from 32 to 9% under 3-h UV and visible irradiation) with a simultaneous increase in their durability due to a decrease in vanadium leaching. An electrolyte with Na2WO4:NaVO3 = 1:3 is optimal for the formation of photoactive and stable composites. When using composites obtained in this electrolyte, MO conversions are 83 and 31% under UV and visible irradiation, respectively. The mechanism of the photocatalytic action of WO3-V2O5-TiO2 composites is considered, and the role of hydrogen peroxide is discussed.

MICROSTRUCTURE AND HIGH-TEMPERATURE WEAR BEHAVIOR OF FE-BASED AMORPHOUS COATINGS BY LASER CLADDING

FeCrMoCB amorphous coatings were prepared on 316 stainless steel via an amorphous powder. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were used to analyze the microstructure, composition, and phase structure of the coatings. Hardness and friction wear testers were applied to investigate the microhardness and wear behavior of the coatings. Results show that the Cr23C6, Cr15Fe7C6 and Fe3Mo crystal phases appeared after laser cladding relative to the complete amorphous powder, and the amorphous phase fraction of the coating was calculated up to 68.4 % using the Verdon method. The coating exhibited a dominating adhesive wear mechanism under room temperature (RT) and transformed to a fatigue wear mechanism as wear test temperature increased to 600 °C. As the temperature was elevated from RT to 600 °C, the wear rate increased from 26 × 10–6 mm3/N·m to 79 × 10–6 mm3/N·m. The laser-cladded Fe-based amorphous coating exhibited much stronger wear performance than the 316 stainless steel, even the wear rate reached one third of that of steel.

Corrosion and Erosion Wear Behaviors of HVOF-Sprayed Fe-Based Amorphous Coatings on Dissolvable Mg-RE Alloy Substrates.

To suppress the corrosion and erosion wear of dissolvable magnesium alloy ball seats in wellbores, Fe-based amorphous coatings were deposited on dissolvable Mg-RE alloy substrates, and their microstructure, corrosion behavior, and erosion wear behavior were studied. The thickness of Fe-based amorphous coatings on dissolvable Mg-RE alloy substrates can reach 1000 μm without any cracks, and their porosity and amorphous contents are 0.79% and 86.8%, respectively. Although chloride ions will damage the compactness and protective efficacy of passive films, Fe-based amorphous coatings still maintain low corrosion current density (3.31 μA/cm2) and high pitting potential (1 VSCE) in 20 wt% KCl solution. Due to their higher hardness, the erosion wear resistance of Fe-based amorphous coatings is about 4.16 times higher than that of dissolvable Mg-RE alloy substrates when the impact angle is 30°. Moreover, the erosion rates of Fe-based amorphous coatings exhibit a nonlinear relationship with the impact angle, and the erosion rate reaches the highest value when the impact angle is 60°. The erosion wear mechanisms of Fe-based AMCs vary with the impact angles, including cutting, delamination, splat fracture, and deformation wear. This work can provide effective guidance for the corrosion and wear protection of plugging tools made from dissolvable magnesium alloy.

The Corrosion Behavior of Al/Al2O3 Composite Films with Ultra-Dense Structure Exposed to Lead-Bismuth Eutectic at 450 to 650 °C

Al2O3 coatings are the most promising candidate material for mitigating (lead-bismuth eutectic) LBE corrosion at elevated temperatures, but preventing inward diffusion of Pb, Bi, and O for the ceramic coating remains a critical challenge. Here, we have fabricated an amorphous Al2O3 coating with an ultra-dense structure by continuous high-power magnetron sputtering (C-HPMS). After LBE corrosion at 550 °C for 2000 h, nanocavities induced by the phase transformation from amorphous to γ-Al2O3 provide the diffusion path for Fe, O, Pb, and Bi in which the corrosion products, such as Fe3O4, PbO2, or their mixed oxides, form. Furthermore, the diffusion of Pb to the substrate and Cr segregation at the interface between the coating and substrate are observed for the sample exposed to LBE at 550 °C for 4000 h. Additionally, the hardness and interface bonding strength are enhanced after LBE corrosion. Moreover, pit corrosion was found to be the main failure mode of coating, and pits that merged with each other induced large area failure at a temperature of 650 °C. The corrosion mechanism of Al2O3 includes element diffusion, phase transformation, and chemical reaction. This work not only provides a deep understanding of the corrosion mechanism of amorphous Al2O3 coatings, but also shows the optimization method on the corrosion resistance of Al2O3 coating.