Preparation of electroless Ni–P composite coatings containing nano-scattered alumina in presence of polymeric surfactant

Ni–P electroless coating was applied on low carbon steel with the incorporation of different amounts of nano Al2O3 powder (ranging from 3 g/l to 30 g/l) in electroless bath. Corrosion properties and microstructures of the coating were studied. The dispersion stability of alumina colloidal particles stabilized by polymeric (non-ionic) surfactants in an electroless bath was also investigated. The surface morphology and the relevant structure were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Corrosion behavior of the coated steel was evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques. The results showed that increasing alumina concentration not only changed the surface morphology, but also promoted the corrosion resistance. Addition of surfactants has an indirect effect on the amount of the incorporated particles. Meanwhile, in the presence of surfactant, corrosion resistance of Ni–P coating containing even a small quantity of alumina was improved since a stabilized bath was obtained.     

Corrosion behavior of Ni–P/nano-TiC composite coating prepared in electroless baths containing different types of surfactant

In current research, in order to enhance the incorporation of nano-sized TiC particles into electroless Ni–P (EN) coating, different types of surfactant (cationic, anionic, and polymeric) were added to the plating bath. The effects of addition of the surfactants on surface morphology, deposition rate, TiC and P contents of the prepared coatings were investigated. The surface morphology was evaluated by scanning electron microscopy (SEM). It was demonstrated that in the presence of the anionic, polymeric and somehow cationic surfactants, TiC nano-particles were embedded in the matrix which influenced the surface morphology. The effect of surfactant types on the corrosion properties of Ni–P/TiC coated steel was also studied. Corrosion behavior of the coated steel was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) which affected by the incorporation of TiC particles into the Ni–P matrix. The level of corrosion resistance improvement depended largely on the phosphorous and TiC concentration of the applied coating.     

Corrosion behaviors of zinc and Zn-Ni alloy compositionally modulated multilayer coatings

Zinc and Zn-Ni alloy compositionally modulated multilayer (CMM) coatings were electrodeposited from dual baths. The coated samples were evaluated in terms of surface appearance, surface and cross-sectional morphologies, as well as corrosion resistance. The results obtained from the salt spray test show that the zinc and Zn-Ni alloy CMM coatings are more corrosion-resistant than the monolithic coatings of zinc or Zn-Ni alloy alone with a similar thickness. The corrosion potential measurement and anodic polarisation tests were undertaken to examine the probable corrosion mechanisms of zinc and Zn-Ni alloy CMM coatings. Analysis on the micrographic features of zinc and Zn-Ni alloy CMM coatings after the corrosion test explains the probable reasons why the Zn-Ni/Zn CMM coatings have a better protective performance. Surface morphologies and compositional analysis of the remaining coating material of Zn-Ni alloy deposit after the corrosion test confirms the dezincification mechanism of the Zn-Ni alloy deposit during the corrosion process.     

Preparation and High Temperature Oxidation Properties of Micro-crystalline MGH754 ODS Alloy Coatings

A special coating technique, electro-spark deposition (ESD), was developed to produce micro-crystalline ODS MGH754 alloy coatings on a commercial 1Cr18Ni9Ti stainless steel and a cast Ni20Cr alloy substrates. The coatings have a very fine grain structure and metallurgical bonding with the substrates. The isothermal oxidation tests at 1000 ℃ in air showed that the micro-crystalline ODS alloy coatings had a much reduced oxidation rate and improved scale spallation resistance compared with the uncoated alloys. The selective oxidation of Cr was greatly promoted to form protective and continuous Cr₂O₃ scales on the alloy surface. Micro-crystallization and oxide dispersions have synergistic effects on the improvement of oxidation resistance. The beneficial effects were discussed based on the experimental results.     

Wear and corrosion resistance of laser-cladded Fe-based composite coatings on AISI 4130 steel

The wear and corrosion resistance of Fe_72.2Cr_16.8Ni_7.3Mo_1.6Mn_0.7C_0.2Si_1.2 and Fe_77.3Cr_15.8Ni_3.9Mo_1.1Mn_0.5C_0.2Si_1.2 coatings laser-cladded on AISI 4130 steel were studied. The coatings possess excellent wear and corrosion resistance despite the absence of expensive yttrium, tungsten, and cobalt and very little molybdenum. The microstructure mainly consists of dendrites and eutectic phases, such as duplex (γ+α)-Fe and the Fe–Cr (Ni) solid solution, confirmed via energy dispersive spectrometry and X-ray diffraction. The cladded Fe-based coatings have lower coefficients of friction, and narrower and shallower wear tracks than the substrate without the cladding, and the main wear mechanism is mild abrasive wear. Electrochemical test results suggest that the soft Fe_72.2Cr_16.8Ni_7.3Mo_1.6Mn_0.7C_0.2Si_1.2 coating with high Cr and Ni concentrations has high passivation resistance, low corrosion current, and positive corrosion potential, providing a better protective barrier layer to the AISI 4130 steel against corrosion.     

Effect of pickling processes on the microstructure and properties of electroless Ni–P coating on Mg–7.5Li–2Zn–1Y alloy

The electroless plating Ni–P is prepared on the surface of Mg–7.5Li–2Zn–1Y alloys with different pickling processes.The microstructure and properties of Ni–P coating are investigated.The results show that the Ni–P coatings deposited using the different pickling processes have a different high phosphorus content amorphous Ni–P solid solution structure,and the Ni–P coatings exhibit higher hardness.There is higher phosphorus content of Ni–P amorphous coating using 125 g/L Cr O3and 110 ml/L HNO3(w68%)than using 180 g/L Cr O3and 1 g/L KF during pre-treatment,and the coating structure is more compact,and the Ni–P coatings exhibit more excellent adhesion with substrate(Fcup to22 N).The corrosion potential of Ni–P coating is improved and exhibits good corrosion resistance.As a result,Mg-7.5Li-2Zn-1Y alloy is remarkably protected by the Ni–P coating.     

Hot-corrosion behavior of Cr2O3-CNT-coated ASTM-SA213-T22 steel in a molten salt environment at 700℃

The present work investigates the hot-corrosion behavior of carbon nanotube (CNT)-reinforced chromium oxide coatings on boiler steel in a molten salt (Na₂SO₄-60wt%V₂O₅) environment at 700℃ under cyclic conditions. The coatings were deposited via the high-velocity oxygen fuel process. The uncoated and coated steel samples were subjected to hot corrosion in a silicon tube furnace at 700℃ for 50 cycles. The kinetics of the corrosion behavior was analyzed through mass-gain measurements after each cycle. The corrosion products were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis techniques. The results revealed that uncoated steel suffered spallation of scale because of the formation of nonprotective Fe₂O₃ scale. The coated steel samples exhibited lower mass gains with better adhesiveness of oxide scale with the steel alloy until the end of exposure. The CNT-reinforced coatings were concluded to provide better corrosion resistance in the hot-corrosion environment because of the uniform dispersion of CNTs in the coating matrix and the formation of protective chromium oxides in the scale.     

Hot-corrosion behavior of Cr_2O_3–CNT-coated ASTM-SA213-T22 steel in a molten salt environment at 700°C

The present work investigates the hot-corrosion behavior of carbon nanotube(CNT)-reinforced chromium oxide coatings on boiler steel in a molten salt(Na_2SO_4–60 wt%V_2O_5) environment at 700°C under cyclic conditions. The coatings were deposited via the high-velocity oxygen fuel process. The uncoated and coated steel samples were subjected to hot corrosion in a silicon tube furnace at 700°C for 50 cycles. The kinetics of the corrosion behavior was analyzed through mass-gain measurements after each cycle. The corrosion products were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis techniques. The results revealed that uncoated steel suffered spallation of scale because of the formation of nonprotective Fe_2O_3 scale. The coated steel samples exhibited lower mass gains with better adhesiveness of oxide scale with the steel alloy until the end of exposure. The CNT-reinforced coatings were concluded to provide better corrosion resistance in the hot-corrosion environment because of the uniform dispersion of CNTs in the coating matrix and the formation of protective chromium oxides in the scale.     

Electrochemical behavior of 304 stainless steel with electrodeposited niobium as PEMFC bipolar plates

In order to enhance the corrosion resistance of 304 stainless steel, niobium was electrodeposited on its surface in air- and water-stable ionic liquids. The electrochemical behaviors of bare and niobium-coated 304 stainless steel were evaluated by electrochemical tests in a simulated proton exchange membrane fuel cell (PEMFC) environment. The results showed that niobium could be electrodeposited on the surface of 304 stainless steel from ionic liquids, and a smooth and strong chemical inert compound film was obtained on the surface of 304 stainless steel, which was mainly composed of NbO and Nb₂O₅. The thin composite film acted as a barrier and remarkably improved the corrosion resistance of 304 stainless steel in the PEMFC environment.     

Corrosion properties of bio-oil and its emulsions with diesel

Bio-oil is a new liquid fuel but very acidic. In this study, bio-oil pyrolyzed from rice husk and two bio-oil/diesel emulsions with bio-oil concentrations of 10 wt% and 30 wt% were prepared. Tests were carried out to determine their corrosion properties to four metals of aluminum, brass, mild steel and stainless steel at different temperatures. Weight loss of the metals immersed in the oil samples was recorded. The chemical states of the elements on metal surface were analyzed by X-ray photoelectron spectroscopy （XPS）. The results indicated that mild steel was the least resistant to corrosion, followed by aluminum, while brass exhibited slight weight loss. The weight loss rates would be greatly enhanced at elevated temperatures. Stainless steel was not affected under any conditions. After corrosion, in- creased organic deposits were formed on aluminum and brass, but not on stainless steel. Mild steel was covered with many loosely attached corrosion materials which were easy to be removed by washing and wiping. Significant metal loss was detected on surface of aluminum and mild steel. Zinc was etched away from brass surface, while metallic copper was oxidized to Cu20. Increased Cr203 and NiO were presented on surface of stainless steel to form a compact passive protection film. The two emulsions were less corrosive than the bio-oU. This was due to the protection effect of diesel. Diesel was the continuous phase in the emulsions and thus could limit the contact area between bio-oil and metals.     

HOVF喷涂Ni–22Cr–10Al–1Y 和Ni–22Cr–10Al–1Y–SiC (N)涂层对ASTM-SA213-T22钢组织和热腐蚀行为的影响

The present paper deals with the investigation of microstructure and high-temperature hot corrosion behavior of high-velocity oxy fuel (HVOF)-produced coatings. Two powder coating compositions, namely, Ni22Cr10Al1Y alloy powder and Ni22Cr10Al1Y (80wt%; micro-sized)–silicon carbide (SiC) (20wt%; nano (N)) powder, were deposited on a T-22 boiler tube steel. The hot corrosion behavior of bare and coated steels was tested at 900°C for 50 cycles in Na₂SO₄–60wt%V₂O₅ molten-salt environment. The kinetics of corrosion was established with weight change measurements after each cycle. The microporosity and microhardness of the as-coated samples have been reported. The X-ray diffraction, field emission-scanning electron microscopy/energy dispersive spectroscopy, and X-ray mapping characterization techniques have been utilized for structural analysis of the as-coated and hot-corroded samples. The results showed that both coatings were deposited with a porosity less than 2%. Both coated samples revealed the development of harder surfaces than the substrate. During hot corrosion testing, the bare T22 steel showed an accelerated corrosion in comparison with its coated counterparts. The HVOF-sprayed coatings were befitted effectively by maintaining their adherence during testing. The Ni22Cr10Al1Y–20wt%SiC (N) composite coating was more effective than the Ni–22Cr–10Al–1Y coating against corrosion in the high-temperature fluxing process.     

Surface modification of Ti-49.8at%Ni alloy by Ti ion implantation: phase transformation,corrosion, and cell behavior

The Ti-49.8at%Ni alloy was modified by Ti ion implantation to improve its corrosion resistance and biocompatibility. The chemical composition and morphologies of the Ti Ni alloy surface were determined using atomic force microscopy(AFM), auger electron spectroscopy(AES), and X-ray photoelectron spectroscopy(XPS). The results revealed that Ti ion implantation caused the reduction of Ni concentration and the formation of a Ti O2 nano-film on the Ti Ni alloy. The phase transformation temperatures of the Ti–Ti Ni alloy remained almost invariable after Ti ion implantation. Electrochemical tests indicated that the corrosion resistance of Ti Ni increased after Ti ion implantation. Moreover, the Ni ion release rate in 0.9% Na Cl solution for the Ti Ni alloy remarkably decreased due to the barrier effect of the Ti O2 nano-film. The cell proliferation behavior on Ti-implanted Ti Ni was better than that on the untreated Ti Ni after cell culture for 1 d and 3 d.     

Pitting corrosion resistance of a novel duplex alloy steel in alkali-activated slag extract in the presence of chloride ions

In this study, two types of reinforcing steels (conventional low-carbon steel and a novel duplex alloy steel with Cr and Mo) were exposed to chloride-contaminated extract solutions (ordinary Portland cement (OPC) extract and alkali-activated slag (AAS) extract) to investigate their pitting corrosion resistance. The results confirm that the pitting corrosion resistance of the alloy steel is much higher than that of the low-carbon steel in both extract solutions with various NaCl concentrations. Moreover, for each type of steel, the AAS extract contributes to a higher pitting corrosion resistance compared with the OPC extract in the presence of chloride ions, likely because of the formation of flocculent precipitates on the steel surface.     

Surface modification of Ti-49.8at%Ni alloy by Ti ion implantation：phase transformation,corrosion, and cell behavior

The Ti?49.8at%Ni alloy was modified by Ti ion implantation to improve its corrosion resistance and biocompatibility. The chemical composition and morphologies of the TiNi alloy surface were determined using atomic force microscopy (AFM), auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The results revealed that Ti ion implantation caused the reduction of Ni concentration and the formation of a TiO2 nano-film on the TiNi alloy. The phase transformation temperatures of the Ti–TiNi alloy remained almost invariable after Ti ion implantation. Electrochemical tests indicated that the corrosion resistance of TiNi increased after Ti ion im-plantation. Moreover, the Ni ion release rate in 0.9% NaCl solution for the TiNi alloy remarkably decreased due to the barrier effect of the TiO2 nano-film. The cell proliferation behavior on Ti-implanted TiNi was better than that on the untreated TiNi after cell culture for 1 d and 3 d.     

Surface Metallurgy of Nickle Base Superalloy

The Double Glow Plasma Surface Alloying Technique, the Xu-Tee Process, is a new method to produce high quality alloying layer on the surface of less expensive materials. By using thes technique, the surface alloying layer similar to superalloy Inconel 625 has been obtained on the surface of three kinds of melallic materials (low carbon steel, industrial pure iron, stainless steel Cr18Ni9). The results of the composition and microstructure analyzed by Scanning Electron Microscopy (SEM) and X-Ray Uffrachon (XRD) show that the alloying layer consistS of y matrix and several precipitates (Laves intermetallic phase and carbide etc.). The electrochemical corrosion results show that the surface alloying layer formed on the surface of stainless steel and industrial pure iron have better corrosion resistance than that of nickel base alloy inconel 625 and stainless steel Cr18Ni9 in 3.5%NaCl solution. The exper iments indicate that it is an effective way to obtain the gradient surface alloying layer on the surfaces of steels by using Double Glow Plasma Surface Alloying Technique.     

Corrosion behavior and mechanism of the automotive hot-dip galvanized steel with alkaline mud adhesion

The corrosion behavior and mechanism of hot-dip galvanized steel and interstitial-free (IF) substrate with alkaline mud adhesion were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and linear polarization. The results show that non-uniform corrosion occurs on the galvanized steel and IF substrate during 250 h with the mud adhesion. The corrosion products on the galvanized steel are very loose and porous, which are mainly ZnO, Zn₅(OH)₈C₁₂·H₂O and Zn(OH)₂, and Fe-Zn alloy layer with a lower corrosion rate is exposed on the galvanized steel surface; however, the corrosion products on IF substrate are considerably harder and denser, whose compositions of rust are mainly FeOOH and Fe₃O₄, and several pits appear on their surface. The results of continuous EIS and linear polarization measurements exhibit a corrosion mechanism, that is, under activation control, the charge transfer resistances present different tendencies between the galvanized steel and IF substrate; in addition, the evolution of linear polarization resistances is similar to that of charge transfer resistances. The higher contents of dissolved oxygen and Cl- ions in the mud play an important role in accelerating the corrosion.     

Dry wear behaviors of wear resistant composite coatings produced by laser cladding

Using different proportional mixtures of Ni-coated MoS₂, TiC and pure Ni powders, new typical wear resistant and selflubricant coatings were formed on low carbon steel by laser cladding process. The microstructures and phase composition of the composite coatings were studied by SEM and XRD. The typical microstructure of the composite coating is composed of multisulfide phases including binary element sulfide and ternary element sulfide, γ-Ni, TiC and Mo₂C. Wear tests were carried out using an FALEX-6 type pin-on-disc machine. The friction coefficient and mass loss of three kinds of MoS₂/TiC/Ni laser clad coatings are lower than those of quenched 45 steel, and the worn surfaces of the laser cladding coatings are very smooth. Because of high hardness combined with low friction, the laser cladding composite coating with a mixture of 70% Ni-coated MoS₂, 20%TiC and 10%pure Ni powder presents better wear behaviors than the composite coating with other powder blends. The composition analysis of the worn surface of GCr15 bearing steel shows that the transferred film from the laser cladding coating to the opposite surface of GCr15 beating steel contains an amount of sulfide, which can change the micro-friction mechanism and lead to a reduced friction coefficient.     

Microstructure characterization of early corrosion behavior of AM60B magnesium alloys

The microstructures and corrosion behavior of AM60B magnesium alloys, produced by both high-pressure die casting (HPDC) and super vacuum die casting (SVDC) processes, were investigated by a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), and slow positron beam technique. XRD confirmed that calcium carbonate (CaCO3) deposited on the surface of alloys during the early stages of corrosion, and the deposition rate of CaCO3 for SVDC with corrosion time was slower than that of HPDC. SEM observation found that the -phases in the skin surface of SVDC alloy had a greater volume fraction and more continuous distribution than that of HPDC alloy, leading to lower volume fraction of CaCO3 deposited on surface of SVDC alloy for the same corrosion time. The slow positron beam Doppler broadening measurement revealed that the thickness of surface corrosion layer increased with corrosion time. Compared with HPDC alloy, the increase rate of thickness for SVDC alloy is slower, which implied that SVDC alloy exhibited a better corrosion resistance than HPDC alloy.     

Microstructural analysis and hot corrosion behavior of HVOF-sprayed Ni–22Cr–10Al–1Y and Ni–22Cr–10Al–1Y–SiC(N) coatings on ASTM-SA213-T22 steel

The present paper deals with the investigation of microstructure and high-temperature hot corrosion behavior of high-velocity oxy fuel(HVOF)-produced coatings. Two powder coating compositions, namely, Ni22Cr10Al1Y alloy powder and Ni22Cr10Al1Y(80 wt%; microsized)–silicon carbide(SiC)(20 wt%; nano(N)) powder, were deposited on a T-22 boiler tube steel. The hot corrosion behavior of bare and coated steels was tested at 900°C for 50 cycles in Na_2SO_4–60 wt%V_2O_5 molten-salt environment. The kinetics of corrosion was established with weight change measurements after each cycle. The microporosity and microhardness of the as-coated samples have been reported. The X-ray diffraction,field emission-scanning electron microscopy/energy dispersive spectroscopy, and X-ray mapping characterization techniques have been utilized for structural analysis of the as-coated and hot-corroded samples. The results showed that both coatings were deposited with a porosity less than2%. Both coated samples revealed the development of harder surfaces than the substrate. During hot corrosion testing, the bare T22 steel showed an accelerated corrosion in comparison with its coated counterparts. The HVOF-sprayed coatings were befitted effectively by maintaining their adherence during testing. The Ni22Cr10Al1Y–20 wt%SiC(N) composite coating was more effective than the Ni–22Cr–10Al–1Y coating against corrosion in the high-temperature fluxing process.     

Effect of nano-SiC particles on the corrosion resistance of NiP-SiC composite coatings

NiP-SiC (≈1 1wt% P) composite coatings were electroplated in a Brenner type plating bath. The coatings had amorphous nano-phase composite structure. Direct current and alternating current electrochemical tests were carried out on such coatings in a 3.5wt% solution of NaCl to evaluate their corrosion resistance. The potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) tests, and exposure experiments all show that the corrosion resistance of NiP-SiC coatings first increases and then decreases when the SiC content increases, but the corrosion resistance of NiP-SiC composite coating is better than that of amorphous NiP coatings.