Effect of Salt Spray Corrosion on Tribological Properties of HVOF Sprayed NiCr-Cr3C2 Coating with Intermediate Layer

The objective of the present work was to determine the influence of the neutral salt spray corrosion on the wear resistance of HVOF sprayed NiCr-Cr3C2 coating with intermediate layer. Ni-Zn-Al2O3 coatings as interlayers were prepared by low pressure cold spray（LPCS） between NiCr-Cr3C2 cermet coatings to form a sandwich structure to enhance the corrosion resistance properties. The tribological properties were examined using the UMT-3 fricition and wear tester by line-contact reciprocating sliding under dry and salt spray one week corrosion. The morphology, element distribution, and phase compositions of the coating and worn sufaces were analyzed by using scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction respectively. The corrosion behavior of the coating was studied by the open-circuit potential, the electrochemical impedance spectroscopy, potentiodynamic polarization, and salt spray corrosion methods. It is found that the sandwich structured coating has better corrosion resistance than the single layer coating. The results show that under dry wear conditions, the wear mechanism is abrasive and adhesive wear, whereas under salt spray corrosion conditions it becomes corrosion wear. The friction coefficient of the sandwich structured coating after salt spray corrosion is slightly lower than the dry friction coefficient, but the weight of the wear loss is lower than that under dry condition.

Enhancement of Active Anticorrosion via Ce-doped Zn-Al Layered Double Hydroxides Embedded in Sol-Gel Coatings on Aluminum Alloy

Ce-doped Zn-Al layered double hydroxide（LDH） nanocontainer was synthesized by a co-precipitation method. X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FT-IR）, scanning electron microscopy（SEM） and transmission electron microscopy（TEM） methods were used for the characterization of the LDH nanocontainer. The anticorrosion activity of the LDH powders embedded in a hybrid sol-gel coating on aluminum alloy 2024 was investigated by electrochemical impendence spectroscopy（EIS）. The results showed that Ce（III） ions were successfully incorporated into LDHs layers. The sol-gel coating modified with Ce-doped Zn-Al LDHs exhibited higher anticorrosion behavior compared with both unmodified and Ce-undoped LDHs containing coatings, which proved the applicability of Ce-doped LDHs in delaying coating degradation and their potential application as nanocontainers of corrosion inhibitors in self-healing coatings.

Effect of Sputtered TiAlCr Coatings on Oxidation and Hot Corrosion Resistance of Ti-24Al-14Nb-3V

The effect of sputtered Ti-50Al-10Cr and Ti-50A1-20Cr coatings on both isothermal and cyclic oxidation resistance at 800-900℃ and hot corrosion resistance at 850℃ of Ti-24Al-14Nb-3V was investigated. Results indicated that Ti-24Al-14Nb-3V alloys exhibited poor oxidation resistance due to the formation of Al2O3+TiO2+AlNbO4 mixed scales in air at 800-900℃ and poor hot corrosion resistance due to the spoliation of scales formed in Na2SO4+K2SO4 melts at 850℃. Both Ti-50Al-10Cr and Ti-50Al-20Cr coatings remarkably improved the oxidation and hot corrosion resistance of Ti-24Al-14Nb-3V alloy.

Influences of substrate temperature on microstructure and corrosion behavior of APS Ni_(50)Ti_(25)Al_(25) inter-metallic coating

In the present investigation, Ni_（50）Ti_（25）Al_（25）（at.%） mechanically alloyed powder is deposited on carbon steel substrate.Before the coating process, the substrate is heated to temperature ranging from room temperature to 400℃. The microstructure, porosity, microhardness, adhesion strength, and corrosion behavior of the coating are investigated at different substrate temperatures. Results show that coating porosity is lower on high temperature surface. Microhardness and adhesion strength of the deposition layer on the substrate without preheating have lower values than with preheating. The polarization test result shows that corrosion performance of the coating is dependent on micro cracks and porosities and the increasing of substrate temperature can improve the quality of coating and corrosion performance.

Properties of Al/Conductive Coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 Composite Anode for Zinc Electrowinning

The properties of Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 composite anode for zinc electrowinning were investigated. The electrochemical performance was studied by Tafel polarization curves（Tafel）, electrochemical impedance spectroscopy（EIS） and corrosion rate obtained in an acidic zinc sulfate electrolyte solution. Scanning electron microscopy（SEM）, X-ray diffraction（XRD）, and energy dispersive X-ray spectroscopy（EDXS） were used to observe the microstructural features of coating. Anodes of Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2, Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC, Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-ZrO2, and Pb-1%Ag anodes were also researched. The results indicated that the Al/conductive coating/α-PbO2-CeO2-TiO2/β-PbO2-WC-ZrO2 showed the best catalytic activity and corrosion resistant performance; the intensity of diffraction peak exhibited the highest value as well as a new PbWO4 phase; the content of WC and ZrO2 in coating showed the highest value as well as the finest grain size.

Corrosion Resistance of Graphene-Reinforced Waterborne Epoxy Coatings

Graphene （G） was dispersed uniformly in water and used as an inhibitor in waterborne epoxy coatings. The effect of dispersed G on anticorrosion performance of epoxy coatings was evaluated. The composite coatings displayed outstanding barrier properties against H20 molecule compared to the neat epoxy coating. Open circuit potential （OCP）, Tafel and electrochemical impedance spectroscopy （EIS） analysis confirmed that the corrosion rate exhibited by composite coatings with 0.5 wt% G was an order of magnitude lower than that of neat epoxy coating. Salt spray test results revealed superior corrosion resistance offered by the composite coating.

Corrosion resistance of a superhydrophobic micro-arc oxidation coating on Mg-4Li-1Ca alloy

A micro-arc oxidation（MAO）/zinc stearate（ZnSA） composite coating was fabricated via MAO processing and subsequent sealing with electrodeposition of a superhydrophobic ZnSA. The surface morphologies,chemical composition and corrosion resistance of the coatings were investigated using field-emission scanning electron microscopy, Fourier transform infrared, X-ray diffraction and electrochemical and hydrogen evolution measurements. Results indicated that the MAO coating was efficiently sealed by the following superhydrophobic ZnSA coating. The MAO/ZnSA composite coating significantly enhanced the corrosion resistance of Mg alloy Mg-4 Li-1 Ca due to its superhydrophobic function. Additionally, corrosion mechanism was suggested and discussed for the composite coating.

Corrosion Resistance of Ti_3Al/BN Abradable Seal Coating

Ti–Al mixed powder（Ti：Al = 3：1 in atomic ratio） and Ti3 Al intermetallic alloy powder mechanically clad hexagonal BN to fabricate Ti Al/BN and Ti3Al/BN composite powders. The corresponding porous abradable seal coatings（named as TAC-1 and TAC-2, respectively） were deposited using vacuum plasma spray（VPS） technology, and their corrosion behavior was studied via salt spray corrosion and electrochemical tests. Phase compositions and microstructures of these coatings before and after corrosion were characterized by X-ray diffraction（XRD） and scanning electron microscopy（SEM） facilitated with energy dispersive X-ray spectrometer（EDS）. The results showed that spontaneous passivation of TAC-1 and TAC-2 granted the coatings excellent corrosion resistance than that of commercial Al/BN coating. Additionally, TAC-2 exhibited higher corrosion potential（Ecorr） and breakdown potential（Ebp） but a lower corrosion current density（icorr） than TAC-1. A small quantity of the corrosion product（Al（OH）3and Al O） could be detected on the surface of TAC-1, while no corrosion product appeared in TAC-2. The non-uniform elements distribution in the metal matrix of TAC-1 resulted in localized corrosion and relatively poor corrosion resistance compared to TAC-2.

Double-layer Modifi cation of Water-based Aluminum with SiO2 and Polyacrylic Acid by Solgel Process and in situ Polymerization

A double-layer aluminum consisting of an aluminum core and a shellof SiO2 and polyacrylic acid was synthesized.This modified aluminum was used to improve the corrosion resistance and dispersive property of aluminum in waterborne media.TEM,FTIR,XPS,and EDX determination showed that PAA and SiO2 were coated on the surface of aluminum.Evolved hydrogen detection showed that the corrosion resistance of composite particle had been markedly improved.Maximum corrosion inhibition efficiency of SiO2 coated aluminum（SiO2@Al）was 95.1% while that of double-layer coated aluminum（PAA/SiO2@Al）was 98.8%.Meanwhile,polyacrylic acid layer improved the agglomeration of aluminum significantly.According to the dispersibility test,the particle size of 50% volume fraction [d（0.5）] of aluminum,SiO2@Aland PAA/SiO2@Alwere 42,53,and 34 μm,respectively.

Hot Corrosion Behavior of a Cr-Modified Aluminide Coating on a Ni-Based Superalloy

A Cr-modified aluminide coating is prepared on a Ni-based superalloy using arc ion plating and subsequent pack cementation aluminizing.Hot corrosion behavior of the Cr-modified aluminide coating exposed to molten Na2SO4/K2SO4（3：1） or Na2SO4/NaCl（3：1） salts at 900 °C in static air are evaluated as well as the aluminide coating.The results indicate that compared with the aluminide coating,the anti-corrosion properties of the Cr-modified aluminide coating in the both salts are improved,which should be attributed to the beneficial effect of the Cr in the coating.The corrosion mechanism of the Cr-modified aluminide coating,especially the role of Cr in the mixture salt corrosion,is discussed.

Influence of Zn and Mg Alloying on the Corrosion Resistance Properties of Al Coating Applied by Arc Thermal Spray Process in Simulated Weather Solution

In this study,Al–Zn and Al–Mg coatings were deposited on steel substrates by an arc thermal spray process.X-ray diffraction and scanning electron microscopy were used to characterize the deposited coatings and corrosion products.Open circuit potential（OCP）,electrochemical impedance spectroscopy,and potentiodynamic studies were used to assess the corrosion characteristics of these coatings after exposure according to the Society of Automotive Engineers（SAE）J2334 solution of varying durations.This solution simulates an industrial environment and contains chloride and carbonate ions that induce corrosion of the deposited coatings.However,the Al–Mg alloy coating maintained an OCP of approximately-0.911 V versus Ag/Ag Cl in the SAE J2334 solution even after 792 h of exposure.This indicates that it protects the steel sacrificially,whereas the Al–Zn coating provides only barrier-type protection through the deposition of corrosion products.The Al–Mg coating acts as a self-healing coating and provides protection by forming Mg_6Al_2（OH）_（16）CO_3（Al–Mg layered double hydroxides）.Mg_6Al_2（OH）_（16）CO_3has interlocking characteristics with a morphology of plate-like nanostructures and an ion-exchange ability that can improve the corrosion resistance properties of the coating.The presence of Zn in the corrosion products of the Al–Zn coating allows dissolution,but,at the same time,Zn_5（OH）_6（CO_3）_2and Zn_6Al_2（OH）_（16）CO_3are formed and act to reduce the corrosion rate.

Preparation and Hot Corrosion Behavior of a NiCrAlY+AlNiY Composite Coating

In this study, a NiCrAIY ＋ AINiY composite coating was prepared by arc ion plating technique and sub- sequent annealing treatment. Cyclic hot corrosion tests of the composite coating and a reference NiCrAIY coating coated with mixed salts of Na2SO4 ＋ K2SO4 and Na2SO4 ＋ NaC1 were carried out at 700 ℃. The results indicated that the composite coating performed better against the corrosion due to the gradient element distribution in Al-enriched outer layer and Cr-enriched inner layer. The corrosion mechanisms for the two coatings were also discussed.

A PASSIVATION STUDY OF Ti-MODIFIED Fe—BASE ALLOY SYNTHESIZED BY MAGNETRON SPUTTERING TECHNIQUE

A set of fracture device was designed on the basis of traditional scratching-electrode technology and used to study the passivation process of two magnetron-sputtered stainless sleel coatings (amorphous and crystalline struture). The results of fracture tests in 3.5 % NaCl aqueous solution show that the amorphous alloy has a high bare surface reactivity and a high passive rate in comparison with the crystalline alloy. The effect of structure on corrosion resistance is also discussed. The excellent corrosion resistance of amorphous alloy is considered to be partly attributed to its great passivation ability.

Protective Composite Coatings Formed on Mg Alloy Surface by PEO Using Organofluorine Materials

The results of the surface modification of magnesium alloys by plasma electrolytic oxidation（PEO） and subsequent treatment in suspension of the superdispersed polytetrafluoroethylene（SPTFE） or telomeric solution of tetrafluoroethylene（TFE） are presented. Composite coatings have been obtained by dipping with subsequent heat treatment. Electrochemical, tribological properties and wettability of protective composite coatings have been investigated. Composite coatings formed on PEO-layer by fourfold treatment of samples in SPTFE suspension possess best protective properties. The obtained coatings decrease the corrosion current density（5.4 × 10^（-11） A cm^（-2）） and wear（7.6 × 10^（-7）mm^3（Nm）^（-1））, and increase the polarisation resistance（1.7 × 10~9 cm^2） and impedance modulus（1.9 × 10~9 cm^2） by orders of magnitude in comparison with unprotected magnesium alloy and base PEO-coating. The highest value of contact angle（CA） has been obtained for coatings with triple application in telomeric solution. CA for such composite coatings attains（171 ± 2）？, as the result of multimodal roughness of the composite coating＇s surface.

Microstructure and Electrochemical Properties of CoCrCuFeNiNb High-Entropy Alloys Coatings

The CoCrCuFeNiNb high-entropy alloys coatings were prepared by using plasma-transferred arc cladding process. The microstructure and electrochemical behaviors of the coating were investigated in detail. The experimental results indicated that the coating consists of a simple fcc solid solution phase and an order（Co Cr）Nb-type Laves phase. The polarization curves, obtained in 1 and 6 mol/L hydrochloric acid solutions, clearly indicated that the general corrosion resistance of the coating at ambient temperature was better than that of 304 stainless steel. The coating displayed a lower corrosion current and lower corrosion rate. Electrochemical impedance spectroscopy demonstrated that the impedance of the coating was significantly higher than that of the 304 stainless steel.

Plasma electrolytic oxidation of the magnesium alloy MA8 in electrolytes containing TiN nanoparticles

The formation of protective multifunctional coatings on magnesium alloy MA8 using plasma electrolyt- ic oxidation （PEO） in an electrolytic system containing nanosized particles of titanium nitride was investigated. Electrochemical and mechanical properties of the obtained layers were examined. It was established that microhardness of the coating with the nanoparticle concentration of 3 gl-1 increased twofold （4.2 ± 0.5 GPa）, while wear resistance decreased （4.97 × 10-6 mm3 N-1 m-1）, as compared to re- spective values for the PEO-coating formed in the electrolyte without nanoparticles （2.1 ± 0.3 GPa, 1.12 × 10.5 mm3 N-1 m-1）.

Electrochemical Characteristics in Seawater for Cold Thermal Spray-Coated Al-Mg Alloy Layer

For corrosion protection of carbon steel in a marine environment,cold arc thermal spray coating was applied to the surface with Al and Al-Mg alloy wires.The surface hardness of Al and Al-Mg thermal spray coatings increased with Mg content.And the various electrochemical experiments were carried out to evaluate corrosion damage characteristics of the thermal spray coating layers.The Al and Al-Mg thermal spray coating layers presented negative potentials compared to carbon steel in corrosion potential measurements.And an anodic polarization experiment revealed a tendency of activation polarization with no passivation.Furthermore,the corrosion damage of the thermal spray coating layer in galvanostatic experiment was observed mainly at the defect area,and the Al-3Mg thermal spray coating layer presented less surface damages than others.In addition,the Al-3Mg thermal spray coating layer showed the lowest corrosion rate while having a sufficient driving voltage for cathodic corrosion protection.Therefore,it is an optimal thermal spray material for sacrificial anode.

Recent progress of vanadium-based alloys for fusion application

Low-activation vanadium alloys,with the reference composition of V-4Cr-4Ti have been considered as one of the most promising candidate materials for structural components such as the blanket in future fusion reactors,thanks to their excellent neutron irradiation resistance,superior high-temperature mechanical properties,and high compatibility with liquid lithium blankets.The self-cooled liquid lithium blanket using structural materials of vanadium alloys is an attractive concept because of the high heat transfer and high tritium breeding capability.After more than 2 decades of research,technological progress has been made in reducing the number of critical issues for application of vanadium alloys to fusion reactors.In this paper,the recent research and development activities of vanadium alloys are summarized,including significant progress achieved on fabrication technology and composition optimization,coating and corrosion,improved understanding of irradiation effects upon microstructure and material properties,retention of hydrogen isotopes,as well as advancements in joining and weld-ing.In particular,the fact that recent products from China,Japan,US and France showed similar properties which meant the fabrication technology has been almost standardized.