Long-term corrosion behavior of HVOF sprayed FeCrSiBMn amorphous/nanocrystalline coating

A FeCrSiBMn amorphous/nanocrystalline coating with 700 μm in thickness and 0.65% in porosity, was prepared by high velocity oxygen fuel(HVOF) spraying process. The long-term corrosion behavior of the FeCrSiBMn coating was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests in a 3.5% NaCl solution with a hard chromium coating as a reference. The FeCrSiBMn coating exhibited higher corrosion potential and lower corrosion current density than the hard chromium coating. The pore resistance(Rp) and charge transfer resistance(Rct) of FeCrSiBMn coating were higher than those of the hard chromium coating. In addition, after immersion in the Na Cl solution for 28 d, only small pores in the FeCrSiBMn coating were observed. All the results indicated that the FeCrSiBMn coating held superior corrosion resistance to the hard chromium coating. This could be attributed to the dense structure, low porosity and amorphous/nanocrystalline phases of the FeCrSiBMn coating.

Identifying the optimal HVOF spray parameters to attain minimum porosity and maximum hardness in iron based amorphous metallic coatings

Flow based Erosion e corrosion problems are very common in fluid handling equipments such as propellers, impellers, pumps in warships, submarine. Though there are many coating materials available to combat erosionecorrosion damage in the above components, iron based amorphous coatings are considered to be more effective to combat erosionecorrosion problems. High velocity oxy-fuel(HVOF)spray process is considered to be a better process to coat the iron based amorphous powders. In this investigation, iron based amorphous metallic coating was developed on 316 stainless steel substrate using HVOF spray technique. Empirical relationships were developed to predict the porosity and micro hardness of iron based amorphous coating incorporating HVOF spray parameters such as oxygen flow rate, fuel flow rate, powder feed rate, carrier gas flow rate, and spray distance. Response surface methodology(RSM) was used to identify the optimal HVOF spray parameters to attain coating with minimum porosity and maximum hardness.

Microstructure and corrosion resistance of Fe/Mo composite amorphous coatings prepared by air plasma spraying

Fe/Mo composite coatings were prepared by air plasma spraying （APS） using Fe-based and Mo-based amorphous and nanocrys- talline mixed powders. Microstructural studies show that the composite coatings present a layered structure with low porosity due to adding the self-bonded Mo-based alloy. Corrosion behaviors of the composite coatings, the Fe-based coatings and the Mo-based coatings were in- vestigated by electrochemical measurements and salt spray tests. Electrochemical results show that the composite coatings exhibit a lower polarization current density and higher corrosion potentials than the Fe-based coating when tested in 3.5wt% NaC1 solutions, indicating supe- rior corrosion resistance compared with the Fe-based coating. Also with the increase in addition of the Mo-based alloy, a raised corrosion re- sistance, inferred by an increase in corrosion potential and a decrease in polarization current density, can be found. The results of salt spray tests again show that the corrosion resistance is enhanced by adding the Mo-based alloy, which helps to reduce the porosity of the composite coatings and enhance the stability of the passive films.

PROPERTIES OF ELECTRODEPOSITED AMORPHOUS Ni-W-P-SiC COMPOSITE COATINGS

The Effects of heat treatment temperature on the hardness,wear resistance and structure of the amorphous Ni-W-P-SiC composite coatings have been investigated.The results show that Ni-W-P-SiC composite coatings are amorphous under 300℃, partially crystalline at 300-400℃,and crystalline when heat treatment temperature reaches 400℃,the crystals being fine Ni3P phase particles.The hardness,wear resistance and the crystallization temperature of the composite coatings increase when an additive is added into the bath.The hardness and wear resistance of the coatings increase with increasing heat treatment temperature,and they will reach their peak values when the heat treatment temperature reaches 400℃.Corrosion experiment indicates that the corrosion resistance of amorphous Ni-W-P-SiC composite coatings in various kinds of corrosive media except nitric acid is better than that of stainless steel 1Cr18Ni9Ti.Scanning electron microscopy observation shows that the additive has no effect on the surface appearance of the coatings,but the current density and the pH value have considerable effects on the surface appearance.

Formation and corrosion behavior of Fe-based amorphous metallic coatings prepared by detonation gun spraying

Amorphous metallic coatings with a composition of Fe48Cr15Mo14C15B6Y2 were prepared by detonation gun spraying process. Microstructural studies show that the coatings present a densely layered structure typical of thermally sprayed deposits with the porosity below 2%. Both crystallization and oxidation occurred obviously during spraying process, so that the amorphous fraction of the coatings decreased to 54% compared with fully amorphous alloy ribbons of the same component. Corrosion behavior of the amorphous coatings was investigated by electrochemical measurement. The results show that the coatings exhibit extremely wide passive region and low passive current density in 3.5% NaCl (mass fraction) and 1 mol/L HCl solutions, which illustrates excellent ability to resist localized corrosion.

Microstructure of Cu-based Amorphous Composite Coatings on AZ91D Magnesium Alloy by Laser Cladding

To improve the sliding wear resistance of AZ91D magnesium alloy, Cu-based amorphous composite coatings made of CuaTTi34Zr11Nis and Cu47Ti34Zr11Ni8＋20 wt pct SiC powders were fabricated on AZ91D magnesium alloy by laser cladding, respectively. SEM （scanning electron microscopy）, EDS （energy dispersive X-ray spectroscopy）, XRD （X-ray diffraction） and TEM （transmission electron microscopy） techniques were employed to study the phases of the coatings. The results show that the coatings mainly consist of amorphous phase and different intermetallic compounds. The reason of formation of amorphous phase and the function of SiC particles were explained in details.

ELECTRODEPOSITION OF AMORPHOUS Ni-P ALLOY COATINGS

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Fabrication and microstructure of Fe-based amorphous composite coatings by laser cladding

Fe-based amorphous composite coatings were fabricated on AISI 1045 steel by laser cladding. The results of the X- ray diffraction and transmission electron microscopy analyses .show the coating is composed of an amorphous phase in majority and a nanocrystaUine phuse in m,inority. Phase composition of the coating changes along the depth of the coating. The reasonable scanning speed for fabricating an amorphous composite coating is 3 500 mm/min when the laser power is 4 800 W and the laser beam diameter is 2 mm. If the scanning speed is lower than 3 500 mm/min, the intensity of the two main diffraction peaks in X-ray diffraction patterns of the coatings decreases with the scanning speeds increasing. At the same time, a broad halo peak emerges and enlarges. High laser power and fast scanning speed are the essential conditions of amorphization. The coating exhibits high microhardness.

Molybdenum based amorphous and nanocrystalline coatings prepared by high velocity oxy-fuel spraying

The high velocity oxy-fuel(HVOF) based thermal spray process has developed as a potential advantageous approach for fabricating various kinds of functional coatings.In this article,the coatings of Mo-based alloy were synthesized using the HVOF process.The microstructure and the mechanical properties of the HVOF-processed coatings were investigated using SEM,TEM,XRD,and hardness and wear tests.Annealing treatment was applied to the as-sprayed coatings to develop the microstructure and its effect on the microstructure and mechanical properties of the coatings was examined.It is found that the HVOF-processed Mo-based alloy coatings are comprised of an amorphous splat matrix embedded with nano-sized crystalline particles.Annealing at temperatures over 950 ℃ results into crystallization of the amorphous matrix.The mechanical properties of the as-sprayed coatings are enhanced with annealing temperature up to 750 ℃ and from 950 to 1050 ℃,keeps constant between 750 and 950 ℃,and reduce over 1050 ℃.The change of the mechanical property with the microstructure was illustrated in the study.

Friction and Wear Properties of Amorphous Carbon Nitride Coatings in Water Lubrication

The friction and wear properties of amorphous carbon nitride(a-CN x)coatings in water lubrication were reviewed.The influences of mating materials and tribological variables such as normal load(W)and sliding speed(V)on the friction and wear properties of the a-CN x coatings were analyzed.It was indicated that the specific wear rate of the a-CN x coatings was related to the hydration reaction of mating materials with water.If the mating materials were easily hydrated,the specific wear rate of a-CN x coatings was low.The water-lubricated properties of the a-CN x coatings were better in comparison to the a-C coatings.The a-CN x/Si-based non-oxide ceramics tribo-pairs exhibited the lowest friction coefficient and wear rate.To describe their friction and wear properties at the normal loads of 3—15Nand the sliding speeds of 0.05—0.5m/s,the wear-mechanism maps for the a-CN x/SiC(Si3N4)tribo-pairs in water were developed.

Effect of TiC addition on the microstructure and wear resistance of induction brazed nickel-based coating in air

The nickel-based coating with different TiC addition was fabricated onto 45 steel substrate by using induction brazed technology in air.The effect of TiC addition on the microstructure and wear resistance of induction brazing coating was studied.The results show that the microstructure of brazing coating is strengthened and refined by adding TiC.With the increase of the amount of TiC added,the amount of TiC in the Ni-based matrix is increased,and the matrix structure is obviously refined.This is because the high melting point TiC particles can be used as heterogeneous nucleation cores,thus refining the Ni based matrix structure.Moreover,the wear resistance of brazing coating is improved due to the addition of TiC.

Influence of Heat Treatment on Microstructure and Mechanical Properties of Plasma Sprayed FeCrMoCBY Amorphous Coatings

The changes of the microstructure and the mechanical properties of FeCrMoCBY amorphous coatings prepared by plasma spraying after heat treatment were investigated.300,400,500 and 600℃were selected as the heat treatment temperature,and the crystallization phenomenon occurred after the heat treatment at 600℃.The crystallization products of the coating heat-treated at 600℃were a-Fe and Fe23(C,B)6.Heat treatment was beneficial to the microhardness and the bonding strength of the coatings.The microhardness of the coating heat-treated at 600℃increased obviously,and the strongest bonding strength occurred in the coating heat-treated at 500℃.The improvement of the wear resistance of the coatings could attribute to heat treatment as well,and the wear resistance of the coating heat-treated at 600℃was the optimum,compared with the coating heat-treated at 500℃.

Fe-based amorphous coating prepared using high-velocity oxygen fuel and its corrosion behavior in static lead-bismuth eutectic alloy

The Fe_(949.7)Cr_(18)Mn_(1.9)Mo_(7.4)W_(1.6)B_(15.2)C_(3.8)Si_(2) amorphous coating was deposited on T91 steel substrate by using the high-velocity oxygen fuel(HVOF)spray technique to enhance the corrosion resistance of T91 stainless steel in liquid lead-bismuth eutectic(LBE).The corrosion behavior of the T91 steel and coating exposed to oxygen-saturated LBE at 400℃ for 500 h was investigated.Results showed that the T91 substrate was severely corroded and covered by a homogeneously distributed dual-layer oxide on the interface contacted to LBE,consisting of an outer magnetite layer and an inner Fe-Cr spinel layer.Meanwhile,the amorphous coating with a high glass transition temperature(Tg=550℃)and crystallization temperature(T_(x)=600℃)exhibited dramatically enhanced thermal stability and corrosion resistance.No visible LBE penetration was observed,although small amounts of Fe_(3)O_(4),Cr_(2)O_(3),and PbO were found on the coating surface.In addition,the amorphicity and interface bonding of the coating layer remained unchanged after the LBE corrosion.The Fe-based amorphous coating can act as a stable barrier layer in liquid LBE and have great application potential for long-term service in LBE-cooled fast reactors.

Amorphous coatings deposited on aluminum alloy by plasma electrolytic oxidation

Amorphous [Al-Si-O] coatings were deposited on aluminum alloy by plasma electrolytic oxidation (PEO). The process parameters, composition, micrograph, and mechanical property of PEO amorphous coatings were investigated. It is found that the growth rate of PEO coatings reaches 4.44 μm/min if the current density is 0.9 mA/mm2. XRD results show that the PEO coatings are amorphous in the current density range of 0.3 - 0.9mA/mm2. EDS results show that the coatings are composed of O, Si and Al elements. SEM results show that the coatings are porous. Nano indentation results show that the hardness of the coatings is about 3 - 4 times of that of the substrate, while the elastic modulus is about the same with the substrate. Furthermore, a formation mechanism of amorphous PEO coatings was proposed.

PREPARATION AND PROPERTIES OF HYDROGEN STORAGE MATERIAL TiFe WITH AMORPHOUS Si COATING

An evident improvement on activation properties of hydrogen storage was made by sput- tering an amorphous coating of commercial Si on TiFe alloy.SEM observation revealed an obvious difference between the morphologies before and after hydrogen storage for TiFe alloy with or without amorphous Si coating.It is believed that this may be quite a developable hydrogen storage material.

Microstructure characteristics of coating with amorphous phases prepared from Fe-based alloy powders by plasma spray

In this paper, alloy powders mixed with a molar ratio of Fe ： P ： C of 80 ： 13 ： 7 were sprayed on Q235 steel by plasma spray method to prepare coating with amorphous phases. The phase composition of the mixed alloy powders and prepared coating were characterized by X-ray diffraction （ XRD ）. The morphology and the composition cf the coating were analyzed by scanning eleetron microscopy （SEM） nnd energy dispersive apectroscopy （ EDS ）. In addition, the thermal stability ef the coating with amorphous phases was characterized by differential thermal analyzer （ DTA ）. Tile results showed that, usirtg mixed alloy powders with a molar ratio of Fe： P： C of 80：13：7, the coating containing certain amount of amorphous alloys was suceessathlly prepared through atmospheric plasma spray technique. In the coating, the main phases were determined to be Fe, FeP aad Fe2P. The crystallization of the coating started from about 461°. Tile coating was mechanically adhered to the substrate.

Fabrication of Ni34.1Fe27.9B18Si18Nb2 amorphous matrix coating on mild steel by laser processing

Ni34.1 Fe27.9B18 Si18 Nb2 coating was deposited on mild steel substrate using high power laser cladding followed by laser remelting process. The laser processing was conducted by the powder feeding method using low purity materials without shielding box. To learn the surface amorphous matrix coating forming mechanism, the coating without remelting process was also studied. The phases and microstructures were analyzed by X-ray diffraction （XRD）, scanning- and transmission-electron microscopy（ SEM, TEM）. The microhardness and corrosion resistance property of the coating were also measured. The results of SEM, XRD and TEM analysis show that the remelted coating has an amorphous matrix layer embedded with some crystals due to high cooling rate during remelting process. The crystals phases are identified as Fe2 B phase, γ （Fe, Ni ） phase and α- Fe phase. No oxidation phases are found in the coating surface. Hardness profiles reveal microhardness more than 1 100 HVo.5 over the full depth of the amorphous matrix layer, while the unremtled coating and the substrate show relatively lower hardness than the remelted layer. Corrosion resistance tests exhibit that the remelted coating is nobler than the unremelted coating and the substrate material.

Process-structure-property relationship for plasma-sprayed iron-based amorphous/crystalline composite coatings

This study explores the fabrication of Fe-based amorphous/crystalline coating by air plasma spraying and its dependency on the coating parameters(plasma power,primary gas flow rate,powder feed rate,and stand-off distance).X-ray diffraction of the coatings deposited at optimized spray parameters showed the presence of amorphous/crystalline phase.Coatings deposited at a lower plasma power and highest gas flow rate exhibited better density,hardness,and wear resistance.All coatings demonstrated equally good resistance against the corrosive environment(3.5wt%NaCl solution).Mechanical,wear,and tribological studies indicated that a single process parameter optimization cannot provide good coating performance;instead,all process parameters have a unique role in defining better properties for the coating by con-trolling the in-flight particle temperature and velocity profile,followed by the cooling pattern of molten droplet before impingement on the substrate.

Effect of Kerosene Flowing Rate on Microstructure and Wearing Properties for Fe-based Amorphous Coatings

The effects of kerosene flow rate on the microstructure and wearing properties were investigated for Fe-based amorphous coatings sprayed by High Velocity Oxygen Fuel (HVOF).The microstructures and wearing properties of the Fe-based amorphous coatings were analyzed with scanning electron microscope (SEM),X-ray diffraction analyzer (XRD),and ball-on-disc tribometer (CFT-1),respectively.The experimental results show that the well interfacial bonding can be observed between the amorphous coating layer and the substrate,and the porosity in amorphous coating layer is less to 1%.Only some crystalline a-Fe and FeO phases can be detected by XRD in the amorphous coatings,while the amorphous content is up to 99.4%.The wearing coefficient is near to 0.15,which is superior to SUS316 of 0.28.As the increasing of wearing loads,the failure mode is changed from oxidation wear to the composite of oxidation and abrasive wear.

Na_2SO_4- and NaCl- Induced Hot Corrosion Behaviors of a Nickel-Base Superalloy with Aluminide Diffusion Coating

Hot-corrosion behaviors of nickel-base superalloy and aluminide diffusion coating have been investigated in conditions of contents of Na2SO4 and NaCI molten salts at 900℃ by means of XRD and SEM. Hot-corrosion scale of the superalloy and aluminide diffusion coating were analyzed and their surface morphologies were observed. The results demonstrate that both coated and uncoated specimens are not susceptible to various contents of NaCI. That may be resulted from the AI2O3 scale formation. Growth stress was characterized by the formation of convoluted scales.