Fe-based Amorphous Coatings Research Articles

Pitting mechanism in a stainless steel-reinforced Fe-based amorphous coating

There is keen interest in developing Fe-based amorphous composite coatings with superior bonding strength and mechanical properties for load-bearing applications. However, the interfaces between the added second phase and the amorphous matrix always suffer from pitting corrosion in harsh Cl− solutions, leading to the degradation of performance of these composite coatings. The underlying pitting mechanism has remained elusive. In this study, the pits initiation behaviour of a Fe-based amorphous coating reinforced with stainless steel powders is systematically investigated in a 3.5% NaCl solution through polarization, electrochemical noise, scanning Kelvin probe and ‘in-situ observation’ measurements, as well as high-resolution transmission electron microscopy. The pitting resistance was found to be deteriorated obviously when stainless steel phase was added to the amorphous coating. The results indicated that pitting at the interfaces was not caused, as generally believed, by microgalvanic corrosion between the stainless steel phase and the amorphous matrix, but caused by the formation of Fe3O4 oxide at the interfaces due to the strong tendency towards oxidation of stainless steel particles in thermal spraying processes. This oxide is unstable in a Cl−-containing environment and acts as reactive sites for pits initiation. The present work emphasizes the effect of oxidation of the reinforcement on the pitting resistance of amorphous coatings and provides an alternative recommendation to the design of amorphous composite coatings for corrosion and load-bearing applications.

Wear resistance of Fe-based amorphous coatings prepared by AC-HVAF and HVOF

Fe63Cr8Mo3.5Ni5P10B4C4Si2.5 amorphous coatings have been prepared by the activated combustion high velocity air fuel (AC-HVAF) and high velocity oxygen fuel (HVOF) processes. The microstructure and wear resistance of the amorphous coatings are comparatively studied. The wear volume loss of the AC-HVAF coating is approximately seven times less than that of the HVOF coating, indicating that the AC-HVAF coating exhibits better wear resistance. Detailed analysis on the worn surface indicates that the enhanced wear resistance of the AC-HVAF coating is mainly attributed to the formation of a more stable oxide tribolayer and smoother worn surface, which result from the dense and complete amorphous microstructure of the AC-HVAF coating. The wear mechanism of the amorphous coatings is dominated by oxidation wear.

Effect of Mo Content on the Corrosion Resistance of Fe-Based Amorphous Composite Coating

A Fe-based amorphous composite coating doped by molybdenum was fabricated by the pulse laser cladding technology. The substrate was a low carbon steel plate. The nominal composition of the powder in the range from 100 to 200 meshes was (wt.%) Cr:14.95, Mo:25.7, B:1.24, C:3.45, Y:3.40, Fe:51.29, which was selected for the laser cladding process. The microstructure, phase composition, hardness and corrosion resistance of the coatings were characterized by means of SEM, EDS, XRD , DSC and potentiodynamic polarization test. The results show that the coating which was composed of amorphous and nanocrystal phases had the dense structure and metallurgical bonding with the substrate, meanwhile with low porosity and cracks. The addition of molybdenum played an important role in improving the corrosion resistance of the coatings. With the increasing content of molybdenum, the hardness had no significant change, while the corrosion resistance of the coatings significantly increased. From the results of polarization curves, the corrosion current density of the coating added 0 wt.% Mo is higher than that of the coatings added 2 wt.% Mo and 10 wt.% Mo. The molybdenum has a superior effect on the corrosion resistance in Fe-based amorphous composite coating.

Microstructure and Properties of Fe-Based Amorphous Composite Coating Prepared by Pulse Laser

The Fe-based amorphous composite coatings were prepared by pulse laser cladding method. The amorphous powder with the size ranging from 100 to 200 meshes was cladded on the low carbon steel plate,and the nominal composition of the powder was (wt.%) Cr:14.95, Mo:25.7, B:1.24, C:3.45, Y:3.40, Fe:51.29. The microstructure, phase composition and hardness were characterized by XRD, SEM, DSC and semi-automatic Vickers hardness tester in this study, respectively. The results show that the coating which is composed of amorphous and nanocrystal phases has the dense structure and metallurgical bonding with the substrate. The hardness of coatings was about 5 times higher than that of the substrate. With the increase of cladding layer, the average hardness of coating showed an increasing trend, and the intrinsic mechanism was discussed.

Laser Brazing Research on Carbon Steel and Stainless Steel Applying Fe-Based Amorphous Coating

The Fe-based amorphous ribbons were prepared by the copper roller melt spinning method, and then the laser brazing was carried out using the amorphous ribbons as the brazing filler metal. Subsequently, laser was used to melt and brazed the plain steel and stainless steel whose surfaces had been pre-coated with the Fe-based amorphous brazing. The micro Vickers hardness tester, metallographic microscope, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the hardness, morphology, microstructure and composition distribution of the welded joints, respectively. The results showed that the prepared amorphous ribbons were of fully amorphous structure. The ordinary steel and stainless steel were well-connected, and mutual dissolution and diffusion had occurred between the solder and the base metal, which achieved the metallurgical bonding. The Fe-based amorphous ribbons were used to solder heterogeneous sheet metals that were difficult to be welded directly. New attempts were made in the hard-connected metal plate field, and the paper could provide concrete references for soldering metals with low invasion, which is of great significance in promoting the development and application of amorphous brazing.

Wear behaviors of Fe-based amorphous composite coatings reinforced by Al2O3 particles in air and in NaCl solution

Abstract In this paper, the influence of the addition of Al2O3 particles on the microstructure and wear properties of Fe-based amorphous coatings prepared by high velocity oxygen fuel (HVOF) has been studied. The wear behaviors of the composite coatings were evaluated against Si3N4 in a pin-on-disk mode in air and in 3.5 wt.% NaCl solution. It was found that the Al2O3 particles were homogenously distributed in the amorphous matrix and the composite coatings exhibited improved wear resistance and reduced coefficient of friction (COF) in both air and wet conditions as compared to the monolithic amorphous coating. The composite coating reinforced with 20 wt.% Al2O3 particles exhibit the best wear performance, which, for example, has extremely low COF (

Microstructure and Wear Behavior of Laser Clad Multi-layered Fe-based Amorphous Coatings on Steel Substrates

Single and multi-layered (with two and three layers) coatings of Fe48Cr15Mo14Y2C15B6 amorphous alloy were applied to AISI 1018 steel substrates via laser cladding. XRD analysis indicated partial retention of the amorphous phase along with the formation of oxide and carbide phases. Cross-sectional SEM micrographs revealed relatively sound coatings laser clad with single layer of amorphous alloy; however, cracks and voids were observed in the two and three layered amorphous coatings. The specimens with single and two layered amorphous coatings exhibited surface hardness of about 650 VHN while the hardness of the specimens with three layered amorphous coatings (~1100 VHN) nearly equaled the hardness of previously reported sintered amorphous alloys of similar compositions. The ball-on-disc wear analysis demonstrated a reverse trend wherein the single and two layered amorphous coatings exhibited lower weight loss during the wear test cycle due to superior surface soundness while the three layered amorphous coatings showed aggravated wear due to internal voids and cracks.

Effect of laser remelting on the microstructure and corrosion resistance of plasma sprayed Fe-based coating

Fe-based amorphous and nanocrystalline coatings were fabricated by air plasma spraying. The coatings were further treated by laser remelting process to improve their microstructure and properties. The corrosion resistance of the as-sprayed and laser-remelted coatings in 3.5wt% NaCl and 1 mol/L HCl solutions was evaluated by electrochemical polarization analysis. It was found that laser-remelted coating appeared much denser than the as-sprayed coating. However, laser-remelted coating contains much more nanocrystalline grains than the as-sprayed coatings, resulting from the lower cooling rate in laser remelting process compared with plasma spraying process. Electrochemical polarization results indicated that the laser-remelted coating has great corrosion resistance than the as-sprayed coating because of its dense structure.

Corrosion and erosion–corrosion behaviour of activated combustion high-velocity air fuel sprayed Fe-based amorphous coatings in chloride-containing solutions

Corrosion and erosion–corrosion (E–C) behaviour of the AC-HVAF sprayed FeCrMoMnWBCSi amorphous metallic coating (AMC) were investigated. Compared with the HVOF AMC, the AC-HVAF AMC presents relatively denser structure with lower porosity and almost nonexistent oxides, which holds higher ability to resist uniform corrosion and pitting owing to the impact structure and the low donor density in the passive film. The enhanced E–C resistance of AC-HVAF AMC could be related to the high hardness and compact structure resulting in the low erosion and synergy weight loss.

Effect of heat treatment on the structure, cavitation erosion and erosion–corrosion behavior of Fe-based amorphous coatings

In this study, high-velocity oxygen-fuel sprayed amorphous coatings have been heat treated at various temperatures to form microstructures with crystalline phases. The structure, micro-hardness, cavitation erosion resistance and erosion–corrosion resistance of these coatings are compared. Crystalline phases are discovered in the coatings after heat treatments at 650°C and 750°C. The coating heat treated at 750°C exhibits the poorest cavitation erosion resistance in 3.5wt% NaCl solution among all coatings due to the degraded corrosion resistance. However, the hardness of the crystallized coating can reach 1000Hv and the erosion–corrosion resistance of the heat treated coating is better than the untreated one.

Fabrication and characterization of Fe-based amorphous coatings prepared by high-velocity arc spraying

Abstract Fe-based coatings with a high amorphous content were firstly developed by the traditional twin wires arc spray technology. In consideration of empirical rules, including the multi-component system, an optimal concentration of small atoms, negative heat of mixing and an appropriate atom size mismatch among the main components, the cored wires were designed to contain eight elements, which have an optimized atomic volume strain criterion λ n , in range of 0.14–0.21, to render the coatings a high glass forming ability. Then the coatings were prepared using the above-designed cored wires through a rapid arc spray melting and solidification process. Crystalline phases could not be identified from the XRD patterns within the XRD resolution limits, suggesting that the as-sprayed coatings were approximately comprised of fully amorphous phases. With a dense structure and a low porosity of only 2%, the amorphous Fe-based coatings exhibited an attractive combination of high hardness (900–1100 HV 0.3 ) and superior bonding strength (44.9–54.8 MPa). The coating at λ n = 0.21 had the lowest Gibbs free energy difference Δ G , exhibited the largest super-cooled liquid region Δ T x , Lu’s criterion factor γ value and the heat of crystallization (Δ H ) values, which indicating the highest GFA.

Enhancement of oxidation and wear resistance of Fe-based amorphous coatings by surface modification of feedstock powders

Abstract Surface oxidation of the in-flight powders during the preparation of amorphous coatings in high velocity oxygen fuel process causes the formation of oxygen-rich intersplat regions. These regions are brittle in nature and can dramatically deteriorate the mechanical performance of the coatings. To solve this problem, the starting FeCrMoCBY amorphous feedstock powders were modified by electroless plating a thin layer of Ni–W–P amorphous phase. It was found that the covering of the Ni–W–P layer can significantly reduce the oxygen content in the resultant Fe-based amorphous coatings. The wear resistance of the coatings with and without the modification of Ni–W–P thin layer was comparatively studied by ball-on-disk wear tests against Si3N4 counterpart in air. It revealed that the wear of two types of coatings follows the same oxidation wear mechanism but the modified coating exhibits much better wear resistance due to the improved oxidation resistance.

Fe-Based Amorphous Composite Coating Prepared by Plasma Remelting

Fe-based amorphous composite coating was deposited on the carbon steel substrate by arc spraying and then remelted by a plasma remelting system, in order to improve the mechanical properties of the coatings. The composition, microstructure, and properties of the composite coating were analyzed by means of the metallographic microscope, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and microhardness tester. The results showed that the amorphous composite coatings had more homogeneous and finer microstructure after the plasma remelting. The coating is metallurgically bonded with the substrate, and the hardness of the Fe-based amorphous composite coating is up to 1220 HV. The internal relationship between microhardness and microstructure has been discussed.

新型Fe 基非晶复合涂层的制备及性能研究

新型Fe 基非晶复合涂层的制备及性能研究

Influence of Spray Parameters on Sliding Wear Properties of HVOF Sprayed Fe-Based Amorphous Coatings

Amorphous powders of Fe-10.7%W-4.5%Cr-4.1%B-3.6%Ni-3.5%Si-2.1%Mo-1.2%C-0.7%Mn were sprayed under six sets of spraying parameters using high velocity oxy-fuel spraying. Phase structure of coatings as well as microstructure is found to be strongly affected by spraying parameters. Sliding wear resistance of amorphous coatings benefits significantly from less porosity and oxides. In addition, evidence correlation is found between amorphous content and wear resistance of coatings. Coating with the best wear resistance exhibits the wear rate of only 2.84×10-6 mm3/(N·m), equals 1.70% and 217% of cast 316L stainless and HVOF-sprayed Cr3C2-NiCr coating respectively.

Influence of Cold Gas Spray process conditions on the microstructure of Fe-based amorphous coatings

Fe-based amorphous metallic coatings were prepared by Cold Gas Spray process. Through this study, the effects of the process conditions such as spraying distance, gas pressure and temperature on the microstructure of as-sprayed coatings are evaluated. Microstructural studies show that the coatings can present a densely layered structure with porosity below 0.5% and thickness around 800μm depending on the process conditions. Precipitation of nanocrystals in as-sprayed coatings is observed and present results show its dependence on the thermal and kinetic energy implicated in the process. In general, when gas temperature and pressure decreased, in the studied range, coatings displayed a dense and amorphous structure.

Properties of Fe-based Amorphous Alloy Coatings with Al2O3-13% TiO2 Deposited by Plasma Spraying

An amorphous alloy composite coatings containing Fe71Cr5B4Si4Ni3Mo3W10 (wt%) and different mass fractions of Al2O3-13%TiO2 ceramic particles were successfully deposited onto plain carbon steel by atmospheric plasma spraying. The microstructure, the micro-hardness and the corrosion resistance properties of the coatings were investigated. The mutual diffusion among Fe, Ti, W, Al and O elements was found at the interface of ceramic particles and Fe-based amorphous matrix. The micro-area metallurgical combination could reduce the porosity generated by the addition of the second phase and enhance the bonding strength between the two phases. The micro-hardness of the composite coating increased by 20% when the addition amount of Al2O3-13%TiO2 was more than 16 wt%. The corrosion resistance ability of the composite coatings was better than that of 1Cr18Ni9Ti stainless steel in10 wt% NaOH solution.

The effect of high-velocity oxy-fuel spraying parameters on microstructure, corrosion and wear resistance of Fe-based metallic glass coatings

Fe-based amorphous coatings were deposited on 1Cr18Ni9Ti stainless steel substrates by high velocity oxy-fuel spraying (HVOF) at different spraying parameters. It has been found that the amorphous phase content of the as-sprayed coatings rises initially and declines later with the increase of spraying power, which is due to the competition between melting and oxidation degree of the feedstock powder and the thermal radiation effect of the flame. Besides, the microhardness and wear resistance of the as-sprayed coatings increase with increasing spraying power, which is attributed to the enhancement of splat-to-splat binding force at elevated spraying power. Moreover, the three kinds of Fe-based amorphous coatings obtained under different spraying parameters all exhibit better corrosion resistance than 316L stainless steel. Particularly, the Fe-based amorphous coating deposited at an intermediate spraying power exhibits dense structure as well as the highest amorphous phase content, the best corrosion resistance, and very good wear resistance, showing promising potential as a candidate for surface protective and anticorrosion coatings for the stainless steel.

Microstructure and Mechanical Properties of Fe-based Amorphous Composite Coatings Reinforced by Stainless Steel Powders

In this study, a few Fe-based amorphous matrix composite coatings reinforced with various portions (4, 8 and 16 vol.%) of 316L stainless steel powders have been successfully produced through high velocity oxy-fuel (HVOF) spraying. The microstructure of the composite coatings was systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The main structure of composite coatings remained amorphous while 316L stainless steel splats were distributed homogeneously in the amorphous matrix and well connected with surrounding amorphous phase. Bonding strength of coatings to the substrate was determined by “pull-off” tensile tests. The results revealed that the 316L stainless steel phase effectively improved the bonding strength of amorphous coatings, which is mainly contributed by the strong metallurgical bonding between stainless steel and amorphous splats. The addition of 316L stainless steel also enhanced the ductility and fracture resistance of the coatings due to the ductile stainless steel phases, which can arrest crack propagation and increase energy dissipation.

Effect of feedstock particle sizes on wear resistance of plasma sprayed Fe-based amorphous coatings

Fe-based amorphous coatings were fabricated by plasma spray technology using Fe43Cr16Mo16C10B5P10 powders with different particle sizes (median size of 33μm, 66μm and 84μm, respectively). XRD results indicated that all of the coatings exhibited a large fraction of amorphous phase. The effect of the feedstock particle sizes on the morphology and microstructure of as-sprayed coatings was investigated by SEM and TEM observations. It was found that the smaller the particle size, the denser the structure with the lower porosity and lesser cracks the coating exhibited. The feedstock particle sizes had a significant effect on the wear resistance of coatings. With a decrease in the particle sizes, the porosity decreased and the cohesion at the intersplat regions and the hardness of the coating improved. Hence, the wear resistance of coating was enhanced. Moreover, the sliding velocity also had different influences on the wear resistance of coatings. Raising the sliding velocity could aggravate the oxidation of the coating and lead to a decrease in the wear resistance. The analysis of the worn surfaces of coatings indicated that the dominating wear mechanism of Fe-based amorphous coatings was fatigue wear accompanied with oxidative wear.