Fe-based Alloy Coatings Research Articles

Progress in Microstructure Design and Control of High-Hardness Fe-Based Alloy Coatings via Laser Cladding

Progress in Microstructure Design and Control of High-Hardness Fe-Based Alloy Coatings via Laser Cladding

Multi-layer formation by oxidation and solid-state crystallization of cold sprayed amorphous coatings during dry sliding wear

Amorphous alloy coatings, known for the exceptional wear resistance, have emerged as a key solution for enhancing the wear performance of magnesium alloys under harsh environments. In this study, Fe-based amorphous alloy coatings were deposited on magnesium alloy by cold spraying technology, and the influence of microstructural evolution on the wear performance of coatings under dry sliding wear conditions was discussed. The results showed that a dense adherent oxide layer with a thickness of ∼700 nm comprising nanograins of less than 8 nm was formed at the outmost surface, which played a role of self-lubricating. Underneath, a 1 μm thick nanocrystalline-amorphous layer with nanograins of ∼20 nm dispersed in the amorphous alloy matrix was formed through in-situ crystallization induced by flash temperature. This composite structure prevented the formation of shear bands in amorphous alloys and enhanced the durability. Therefore, the transition from abrasive wear to adhesive wear was a consequence of the microstructural evolution from a dual-phase composite layer to a self-lubricating oxide layer.

Comparative analysis of microstructure and corrosion resistance in laser-clad austenitic and martensitic stainless-steel coatings

Post-casting austenite often possesses better corrosion resistance than martensite. In order to compare the difference of corrosion resistance between austenitic stainless steel coating (ASSC) and martensitic stainless steel coating (MSSC) in the powder metallurgical state, two stainless steel Fe-based alloy coatings of the same process parameter were prepared on the surface of 40Cr steel by using laser cladding technology. Through SEM, EBSD, XRD and electrochemical tests, the microstructure, phase and cross-section metallurgical bonding condition of the coating were studied, and the difference in corrosion resistance between the two was comprehensively analyzed. The results showed that the main phase structure of ASSC was the FCC phase, and the main phase structure of MSSC was the BCC phase. The average self-corrosion current (9.92 × 10−8 A/cm2) and average self-corrosion rate (1.04 × 10−3 g/m2·h) of MSSC were 4.77 % and 5.62 % of ASSC, respectively. In addition, the polarization resistance, impedance value, and passivation film density of MSSC are higher than ASSC, MSSC has less damage from corrosion. The combination of factors, such as fabric refinement and passivation film density, makes the corrosion resistance of MSSC better than ASSC.

Research on Exposure to Salt Water Environment of Fe-based Amorphous Alloy Coating Fabricated by Twin Wire Arc Spray

Research on Exposure to Salt Water Environment of Fe-based Amorphous Alloy Coating Fabricated by Twin Wire Arc Spray

Effect of chromic acid anodization on the corrosion resistance of laser cladding austenitic stainless steel coatings based on orthogonal tests

In this paper, Ni transition layer and Fe-based alloy coatings were prepared on HT250 by laser cladding technology, and the corrosion resistance of the coatings was further enhanced by the chromic acid anodization (CAA) surface treatment process. The effects of time (t), current intensity (I), and temperature (T) on the microstructure and corrosion resistance of the coating after CAA were explored based on the three-factor and three-level orthogonal test method. The results show that after CAA, the intergranular morphology of the coating is corroded, the intragranular organization is exposed and protrudes, and the micro-morphology shows a multi-layer "skeleton" overlapping structure. The main phases were transformed from γ-Fe (FCC) to CrNi (FCC) and FeNi (BCC). The corrosion residue of the original coating is a lamellar metal-carbide weave, whereas the CAA coating is fibrous. The order of influence of CAA process parameters on corrosion depth and maximum impedance value is I >t >T. I on the degree of densification of the passivated film is 1.03 and 1.81 times higher than T and t, respectively. The best corrosion resistance of the sample was obtained at t = 30 min, I = 0.1 A, and T = 40 ℃, and its corrosion rate (2.83 × 10−3 g/m2·h) was 29.88 % lower than the original coating (4.03 × 10–3 g/m2·h).

Study on the Effect of Laser Remelting Energy Density on the Microstructure and Wear Resistance of Fe-Based Alloy Coatings Fabricated by Laser Cladding

Study on the Effect of Laser Remelting Energy Density on the Microstructure and Wear Resistance of Fe-Based Alloy Coatings Fabricated by Laser Cladding

Effect of laser remelting scanning speed on microstructure and abrasion resistance of laser cladded Fe-based alloy coatings

In this work, Fe-based alloy coatings were prepared on ductile iron substrates by laser cladding and laser remelting was used to further improve the abrasion resistance of the coatings. The result shows that increasing the remelting speed can gradually refine the microstructure and fully releases the residual stresses, and the inter-dendritic mesh structure becomes finer and denser. Compared with the original coating, remelted coatings have a significant increase in hardness and hardness uniformity. At the higher remelting speed of 40 mm/s, the coating had the highest hardness and abrasion resistance, 113.08 % and 157.55 % of the original coating, respectively.

High corrosion resistance of a novel armored super-hydrophobic Fe-Mn-Si-Cr-Ni coating

In this work, ultrasonic-assisted laser cladding technology was employed to fabricate shape memory alloy (SMA) coatings composed of Fe-Mn-Si-Cr-Ni on the surface of 304 stainless steel. Both experimental and simulated results unequivocally demonstrate a substantial improvement in both microhardness and wear resistance of the metal surface. Subsequently, a superhydrophobic coating with an “armor-like” structure was comprehensively prepared by integrating femtosecond laser (FSL) and nano SiO2 spray-coating techniques. The creation of this microstructure on the coating surface efficiently facilitated the high-efficiency embedding of nano SiO2 particles. Notably, the modified SMA coating exhibited stable superhydrophobic properties and exceptional corrosion resistance. This research not only provides novel approaches and methods for the preparation and modification of Fe-based memory alloy coatings but also highlights potential applications in the corrosion-resistant field. The work offers valuable insights for researchers in the field of materials science, emphasizing the synergistic effects of ultrasound-assisted laser cladding technology, femtosecond laser, and nano SiO2 spraying techniques. It provides robust support for the development of new functional coatings.

Study on the Performance of Fe-Based Alloy Coating on 40Cr Substrate Surface

Study on the Performance of Fe-Based Alloy Coating on 40Cr Substrate Surface

Microstructure and Properties of FeAlC-x(WC-Co) Composite Coating Prepared through Plasma Transfer Arc Cladding

Tungsten carbide (WC) is widely used in wear-resistant parts due to its excellent wear resistance. Iron-based alloys are used in the repair and remanufacturing of engine components due to their good compatibility with iron-based workpieces. In order to enhance the wear resistance of engine components in service under abrasive conditions, composite coatings have been prepared for cast iron engine components by adding WC-Co to iron-based powders. This study investigates the microstructure and wear properties of composite coatings of iron-based alloys reinforced with different contents of WC particles. The composite coatings mainly contained γ-Fe, α-Fe, WC and Fe3W3C. With the addition of the WC-Co strengthening phase, the average hardness of the FeAlC-x(WC-Co) composite coatings increases from 524 HV0.2 to 814 HV0.2. Wear test results showed that when the WC addition was 20%, it had the lowest frictional coefficient of 0.5 and the lowest wear mass loss of 1.3 mg. Compared to the original Fe-based alloy coatings, the WC particle-reinforced FeAlC composite coatings display improved wear resistance on a reduced friction basis, mainly benefiting from the high wear resistance of the graphite solid lubrication phase and carbides in the cladding.

Effect of ultrasonic high-frequency micro-forging on the wear resistance of a Fe-base alloy coating deposited by high-speed laser cladding process

In this study, Fe-based alloy coatings were prepared on 27SiMn substrates by laser cladding. To eliminate defects such as insufficient coating precision and excessive residual stress, the effects of ultrasonic high-frequency micro-forging (UH-FM) on coating microstructure and wear resistance were investigated. The experimental results show that the coating's surface roughness and residual stress are significantly reduced after UH-FM. The surface microstructure was broken and refined, and a gradient structure appeared. A part of the fcc phase was transformed into the bcc phase, which increased the resistance of dislocation movement, and the hardness of the coating increased. The width and depth of the abrasion marks and the wear weight loss of the treated coatings were reduced, and the compact oxide layer was distributed more uniformly, indicating that the UH-FM-treated coatings obtained better wear resistance.

Microstructure and Mechanical Properties of Fe-Based Alloy Coatings Fabricated by Laser Cladding

The Fe-based alloy coating was prepared on the surface of 25Cr2Ni4MoV steel substrate by laser cladding. The microstructure, microhardness, shear strength, friction and wear properties of the laser cladding coating were systematically studied. The results show that a good metallurgical bond has been formed between Fe-based alloy coating and substrate. The laser cladding layer is a typical dendritic crystal, which is composed of light gray and dark gray phases. The shear strength displacement curve shows the typical characteristics of brittle fracture, with an average shear strength of 280.83 MPa. The average dry friction coefficient, wear track depth and average wear volume of laser cladding Fe-based alloy coatings are (0.45 ± 0.01), (26 ± 3) μm and 0.066615 m3, respectively. The average dry friction coefficient, wear track depth and average wear volume of 25Cr2Ni4MoV substrate are (0.60 ± 0.01), (39 ± 3) μm and 0.13085 m3, respectively. The laser cladded Fe-based alloy coating exhibits much better wear resistance than the steel substrate, and the shear strength of the coating displays its potential for the application in the service environment of shear stress.

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.

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.

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.

Effect of chromic acid anodization on the corrosion resistance of Fe-based alloy coatings by high-speed laser cladding

Fe-based alloy coatings were coated on surface of ductile cast iron by high-speed laser cladding, and the effects of chromic acid anodization on corrosion resistance of coatings were analyzed. The results show that as chromic acid anodization time increases, corrosion rate falls and then rises. After 20 min, the coating had Cr and Fe oxide passivation film, maximum impedance value (5.40 × 105 Ω·cm2) and polarization resistance (50.6 kΩ·cm2), and minimum self-corrosion current (0.77 μA/cm2). Its corrosion resistance had improved significantly.

Investigation of the Microstructure and Wear Properties of Conventional Laser Cladding and Ultra-High-Speed Laser Cladding Alloy Coatings for Wheel Materials

In this paper, Fe-based and Co-based alloy powders were chosen to perform laser cladding on wheel materials through conventional laser cladding (CLC) and ultra-high-speed laser cladding (UHSLC) processes, respectively. The microstructures, element distribution, phase composition and hardness of the Fe-based alloy and Co-based alloy coating layers using the CLC and UHSLC processes were compared and analysed. The results show that the CLC and UHSLC alloy coatings were dense and free of defects such as pores and cracks. Compared with the CLC alloy coating, the grain size of the UHSLC alloy coating was smaller, the coating composition was close to the powder design composition, and the distribution of Cr within and between the grains was more uniform. The Fe-based coating was mainly composed of (Fe, Ni) and Cr7C3, and the Co-based coating was mainly composed of γ-Co and Cr23C6. It was found that the cooling rate of the CLC alloy coating was smaller than that of the USHLC, and the hardness of the CLC alloy coating was less than that of the USHLC. The average hardness of the UHSLC Fe-based and Co-based alloy coatings was 709 HV and 525 HV, respectively. The average hardness of the CLC Fe-based and Co-based alloy coatings was 615 HV and 493 HV, respectively. The rolling friction and wear tests were carried out with the CLC-treated and UHSLC-treated wheel specimens on the GPM-30 rolling contact fatigue testing machine. The results showed that the wear rate of the UHSLC alloy coating on the wheel specimens was significantly lower than that of the CLC alloy coating on the wheel specimens. The wear rates of the UHSLC Fe-based and Co-based alloy coatings on the wheel specimens were reduced by 40.7% and 73.8%, respectively. It was demonstrated that the wear resistance of the USHLC alloy coatings was better than those of the CLC alloy coatings. The CLC alloy coating exhibited more severe fatigue damage with small cracks. Furthermore, the damage of the UHSLC alloy coating was relatively minor, with slight spalling. The Co-based alloy coating exhibited superior wear properties with the same laser cladding process.

Effect of high-temperature heat treatment on electrochemical corrosion behavior of laser cladding Fe-based alloy coating in H2SO4 solution

Double-layer Fe-based alloy coatings were fabricated on the surface of ductile cast iron using high-speed laser cladding. The electrochemical corrosion behavior of the coatings in 0.5 mol/L H2SO4 solution was analyzed after heat treatment (HT) at 950 ℃ for 1, 2, and 3 h. The results show that many fine and dispersed particles were precipitated in dendrites after 1 and 2 h HT. The precipitates in the dendrites of the 3 h heat-treated aggregated, nucleated, and grew up, forming the blocky. At the same time, the intergranular part of the long-chain structure began to dissolve and break. The corrosion rate decreased significantly with the increase in HT time. The specimen had the most-nobel self-corrosion potential (−0.15 V) and the best corrosion resistance after 3 h HT.

Effect of boron on the microstructural evolution and wear resistance of high-hardness Fe-based alloy coatings prepared by laser cladding

One of the primary failure modes of 45 steel is severe surface wear, which significantly raises its application cost. In order to improve the wear resistance, high-hardness Fe-based alloy coatings with varying boron contents were prepared on 45 steel substrates by preplaced-powder laser cladding in this study. The effect of boron content on the phase composition and microstructural evolution of the coatings were systematically studied. The proportion, morphology, and distribution characteristics of boride phases in the coatings were discussed in detail. The results demonstrated that the Fe-based alloy coatings with different boron contents were composed of α-Fe, Cr7C3, and Fe2B phases. The boron content had a significant influence on the morphology and proportion of the boride phases. With the increase of boron content, the proportion of boride phases gradually increased and the morphology transition was reticular → cluster-shape → long strip-shape → plate-shape. The composition analysis revealed that the boride was Cr-rich Fe2B phase and the content of Cr in the borides increased with the boron content of the coating. The addition of boron could effectively improve the hardness and wear resistance of the Fe-based coatings, which could be attributed to the boride hard phases in the microstructures. The coating with 6.0 wt% B exhibited the highest microhardness and least amount of wear loss. The wear mechanism of the coating with different boron contents was also discussed.

Effect of ultrasonic high-frequency percussion on the microstructure and corrosion resistance of Fe-based alloy coatings by high-speed laser cladding

Fe-based alloy coatings were prepared by high-speed laser cladding (HSLC) technology, and the surface was subjected to ultrasonic high-frequency percussion (UH-FP). The dendrites at the top of the coatings were smaller, and there was dendrite segregation. After UH-FP, the surface profile of the coatings was smoother, achieving the mirror effect. The roughness decreased from 2.643 μm to 0.913 μm and the residual stress of the coatings changed from 306.92 MPa to −92.18 MPa. The electrochemical corrosion behavior in a 3.5 % NaCl solution indicates that the UH-FP coatings exhibit higher corrosion resistance. Anti-corrosion mechanism was discussed based on residual stress and roughness.