Formation mechanism of electroless plating nickel-based composite coating on highly active rare earth magnesium alloys and its corrosion resistance and adhesion performance

The process of preparing anodic oxide film containing active sites and electroless nickel plating on highly active rare earth magnesium alloy was developed.The formation mechanism of electroless nickel plating on active anodic oxide film and the structure and properties of the composite coating were studied by several surface and electrochemical techniques.The results showed that Ag nanograins with an average size of 10 nm were embedded into the anodic oxide film with pores of 0.1−2μm.Ag nanoparticles provided a catalytic site for the deposition of Ni-B alloy,and the Ni crystal nucleus was first grown in horizontal mode and then in cylindrical mode.The corrosion potential of the composite coating increased by 1.37 V and the corrosion current reduced two orders of magnitude due to the subsequent deposition of Ni-P alloy.The high corrosion resistance was attributed to the misaligning of these micro defects in the three different layers and the amorphous structure of the Ni-P alloy in the outer layer.These findings provide a new idea for electroless nickel plating on anodic oxide film.

High corrosion and wear resistant electroless Ni–P gradient coatings on aviation aluminum alloy parts

A Ni–P alloy gradient coating consisting of multiple electroless Ni–P layers with various phosphorus contents was prepared on the aviation aluminum alloy. Several characterization and electrochemical techniques were used to characterize the different Ni–P coatings’ morphologies, phase structures, elemental compositions, and corrosion protection. The gradient coating showed good adhesion and high corrosion and wear resistance, enabling the application of aluminum alloy in harsh environments. The results showed that the double zinc immersion was vital in obtaining excellent adhesion (81.2 N). The optimal coating was not peeled and shredded even after bending tests with angles higher than 90°and was not corroded visually after 500 h of neutral salt spray test at 35℃. The high corrosion resistance was attributed to the misaligning of these micro defects in the three different nickel alloy layers and the amorphous structure of the high P content in the outer layer. These findings guide the exploration of functional gradient coatings that meet the high application requirement of aluminum alloy parts in complicated and harsh aviation environments.

Recent advances in hydrothermal modification of calcium phosphorus coating on magnesium alloy

Magnesium(Mg) and its alloys have emerged as a favored candidate for bio-regenerative medical implants due to their superior biocompatibility, biodegradability and the elastic modulus close to that of human bone. Unfortunately, the rapid and uncontrollable degradation rate of Mg alloys in chloride-rich body microenvironments limits their clinical orthopedic applications. Recently, Calcium Phosphate(Ca-P)biomaterials, especially Hydroxyapatite(HA), have been broadly applied in the surface functional modification of metal-based biomaterials attributed to their excellent bioactivity and biocompatibility. Hydrothermal modification of Ca-P coatings on Mg alloys has been extensively exploited by researchers for its significant superiorities in controlling coating structure and improving interfacial bonding strength for better osseointegration and corrosion resistance. This work focuses on the up-to-the-minute advances in Ca-P coatings on the surface of Mg and its alloys via hydrothermal methods, including the strategies and mechanisms of hydrothermal modification. Herein, we are inclined to share some feasible and attractive hydrothermal surface modification strategies. From the perspectives of hydrothermal manufacturing technique innovation and coating structure optimization, we evaluate how to foster the corrosion resistance, coating bonding strength, osseointegration and antibacterial properties of Mg alloys with Ca-P coatings synthesized by hydrothermal method. The challenges and future perspectives on the follow-up exploration of Mg alloys for orthopedic applications are also elaborately proposed.

Effect of Rare Earth Elements on Depositing Rate of Nickel Alloy Brush Plating Coatings

The effect of four kinds of rare earth elements on the depositing rate of Ni-based alloy brush plating coatings was investigated. The results indicate that all of the selected rare earth elements increase the depositing rate of Ni-based alloy coatings, and Sm increases the depositing rate most obviously. There is an optimum amount of rare earth addition in the plating solution. With the change of plating voltage to a certain extent, the results reveal no differences. The mechanism of the increase of the depositing rate was analyzed.

Microstructure and Performances of Nanocrystalline Zinc-nickel Alloy Coatings

Nanocrystalline zinc-nickel alloy coatings were deposited from an alkaline zincate bath contained an organic additive that can reduce polarization and a complexing agent. SEM and TEM observations and XRD analysis were performed to examine the microstructure and phase composition of the coatings. The nickel content in deposits is 12.0-14.7% and the coating is consisted of single nanocrystalline y-phase structure (Ni5Zn2i), with grain average grain size about 15nm. The nanocrystalline zinc-nickel alloy coatings have better corrosion resistance, less bnttleness and higher microhardness than the conventional zinc coatings.

ELECTRODEPOSITION OF AMORPHOUS Ni-P ALLOY COATINGS

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Nickel and nickel-phosphorous matrix composite electrocoatings

Nickel and nickel-phosphorous matrix composite coatings reinforced by TiO2,SiC and WC particles were produced under direct and pulse current conditions from an additive-free Watts' type bath.The influence of the variable electrolysis parameters(type of current,frequency of current pulses and current density) and the reinforcing particles properties(type,size and concentration in the bath) on the surface morphology and the structure of the deposits was examined.It is demonstrated that the embedding of ceramic particles modifies in various ways the nickel electrocrystallisation process.On the other hand,Ni-P amorphous matrix is not affected by the occlusion of the particles.Overall,the imposition of pulse current conditions leads to composite coatings with increased embedded percentage and more homogenous distribution of particles in the matrix than coatings produced under direct current regime.

Interface characteristics of Al_2O_3－13%TiO_2 ceramic coatings prepared by laser cladding

Al2O3-13%TiO2 （mass fraction） coatings, prepared by laser cladding on nickel-based alloy, were heated using high frequency induction sources. The coating microstructure and the interface between bond coating and ceramic coating were characterized by SEM, XRD and EDS. The results show that two-layer substructure exists in the ceramic coating： one layer evolving from fully melted region where the sintered grains grow fully; another layer resembling the liquid-phase-sintered structure consisting of three-dimensional net where the melted Al2O3 particles are embedded in the TiO2-rich matrix. The mechanism of the two-layer substructure formation is also explained in terms of the melting and flattening behavior of the powders during laser cladding processing. The spinel compounds NiAl2O4 and acicular compounds Cr2O3 are discovered in the interface between bond coating and ceramic coating. It proves that the chemical reactions in the laser cladding process will significantly enhance the coating adhesion.

CRYSTALLISATION KINETICS AND PHASE TRANSFORMATION BEHAVIOUR OF ELECTROLESS NICKEL-PHOSPHORUS DEPOSIT WITH 6-9wt% PHOSPHORUS CONTENT

Crystallisation kinetic and phase transformation behaviour of the electroless nickel-phosphorus deposit with 6-9wt% phosphorus content were studied. The deposit was heated in the differential scanning calorimetry (DSC) apparatus to 300℃-800℃ at 20℃/min, followed by the X-ray diffraction (XRD) analysis. The sequence of crystallisation process was: mixture of amorphous and microcrystalline nickel phases → intermediate metastable, f. c. c. nickel and stable N13P phases → f. c. c. nickel and stable Ni3P phases. Preferred orientation of nickel {200} plane was developed after the heating processes. Activation energy of crystallisation process was determined from the DSC analyses at 5-50℃/min. Crystallisation temperatures were found increased with increasing heating rate.

Oxidation and hot corrosion behaviors of HVAF-sprayed conventional and nanostructured NiCrC coatings

The oxidation and hot corrosion behaviors of HVAF-sprayed conventional and nanostructured NiCrC coatings were studied.The oxidation experiment was conducted in air,and the hot corrosion was conducted in the Na2SO4-30%K2SO4 environment, in the temperature range of 550-750℃for periods up to 160 h.The corrosion kinetics was tested with the thermogravimetric method. The corrosion products were characterized by scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDX)and X-ray diffractometry(XRD).As indicated by the results,both types of coatings possess high corrosion resistance,especially the nanostructured NiCrC coating.The enhanced grain boundary diffusion in the nanostructured coating not only promotes the formation of a denser Cr2O3 scale with a higher rate,but also helps to mitigate the Cr depletion at the metal/scale interface.The less porosity of the nanostructured coating is also thought to be beneficial to the anti-corrosion properties.

Corrosion behavior of NiCrBSi coatings deposited by HVOF spraying

The corrosion resistance of NiCrBSi coating deposited on steel substrate by HVOF was examined using electrochemical tests and immersion tests so as to offer an experimental basis to expand a promising applied field of HVOF in aqueous medium, comparing with those of coatings deposited by oxyacetylene flame spraying and flame cladding. The results show that the general corrosion rate of HVOF sprayed coatings is quite bigger than that of clad coatings, but it is less sensitive to local corrosion. There is less and smaller porosity in the coatings deposited by HVOF than that in flame sprayed coatings. The effects of porosity on the corrosion current density was indistinctive, but the existence of large amount of defects in the coatings damaged the cohesion of the coatings, causing the metallic particles drop off from the coatings under the influence of corrosive medium. Improving the quality and reducing the porosity of coatings is the key to get the coatings with high corrosion resistance.

Coupling a titanium dioxide based heterostructure photoanode with electroless-deposited nickel-phosphorus alloy coating on magnesium alloy for enhanced corrosion protection

The utilization of photoelectrochemical cathodic protection(PECCP)enables an indirect corrosion pro-tection of metals with low self-corrosion potential by introducing a metallic nickel interlayer.However,the ability to enhance the PECCP efficiency remains challenging because of the inherent property of the semiconductor.Herein,this ability is demonstrated by coupling a covalent organic framework(TpBD)dec-orated TiO 2 photoanode(TiO 2/TpBD)with nickel coating on magnesium alloy for an effective corrosion protection.The composite photoanode showed direct PECCP for the nickel interlayer and indirect corro-sion protection of the magnesium alloy.The composite structure of the nanotube array and the covalent organic framework for the photoanode were confirmed by field emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS).The en-hanced photoelectrochemical conversion capability and PECCP performance of the nickel-coated Mg alloy were evidenced by the results from electrochemical and photoelectrochemical measurements including Mott-Schottky curves,photoinduced potential variations,and electrochemical impedance spectroscopy(EIS).Lastly,a corrosion protection mechanism is proposed,where the enhanced PECCP efficiency is at-tributed to the formation of a direct Z-scheme heterojunction,which is substantiated by the results from valence band(VB)XPS and electron spin resonance characterizations.

Experimental Study on Machining Shape Hole of Ni-based Super-heat-resistant Alloy

Inconel 718 and Waspaloy, Nickel-based super-heat-resistant alloy, are high-strength, thermal-resistant and corrosion-resistant alloy that are widely used in parts of gas turbines and airplane engines. Due to their extremely tough and thermal-resistant nature, they are well known as materials that are difficult to cut. Shape holes on a disc of an aircraft engine, made of Ni-based super-heat-resistant alloy, are required with good surface integrity and geometric accuracy. This kind of shape hole is produced by EDM (Electro-discharge machining) currently. It is necessary to investigate an alternative machining process to reduce the process time and improve the surface quality. This paper presents an experimental study on the machining methods for the shape hole of Ni-base super-heat-resistant alloy Inconel 718 and Waspaloy. The feasibility using milling or/and grinding as an alternative for currently EDM process to machine shape holes is assessed by observing the wear and breakage of the cutting tools and grinder and analyzing the hole surface integrity and geometric accuracy. The results show that the milling process of Inconel 718 and Waspaloy can produce shape holes with acceptable surface roughness and geometric accuracy efficiently. The machined Waspaloy shape holes reveal a slight decrease tendency in section dimension from the top of the its bottom. There is a larger deviation from the nominal profile at the segment with smaller radius. A thin softened surface layer with thickness smaller than 60 μm occurs on the machined Waspaloy shape holes. The softening and work hardening become remarkable with the progress of tool wear.

WIDE-BAND LASER CLADDING: WEAR AND CORROSION RESISTANCE OF A Ni-BASED ALLOY

A novel wide-band laser cladding system, with high rate of cladding, has been developed in the present work. The system mainly consisted of a 5kW CO2 laser, an automatic powder feeder and a wide-band scanning rotative polygon mirror which can produce a linear or rectangular focused laser beam. Using this system, a Ni-Cr-Si-B alloy powder was cladded on the surface of type 321 austenitic stainless steel in order to improve its wear and corrosion resistance. The pitting corrosion, high temperature oxidation and wear tests were conducted in order to evaluate the properties of the laser cladded layer. The results demonstrated that the cladded layer can significantly improve the adhesive wear and pitting corrosion resistance of the substrate. Moreover, the cladded layer exhibited good oxidation resistance, which is almost the same as that of GMR-235D Ni-based superalloy.

Facile fabrication of novel cobalt-based carbonaceous coatings on nickel-titanium alloy fiber substrate for selective solid-phase microextraction

Fabrication of selective adsorption coatings plays a crucial role in solid-phase microextraction(SPME).Herein,new strategies were developed for the in-situ fabrication of novel cobalt-based carbonaceous coatings on the nickel-titanium alloy(Ni Ti)fiber substrate using ZIF-67 as a precursor and template through the chemical reaction of ZIF-67 with glucose,dopamine(DA)and melamine,respectively.The adsorption performance of the resulting coatings was evaluated using representative aromatic compounds coupled to high-performance liquid chromatography(HPLC)with ultraviolet detection(HPLC-UV).The results clearly demonstrated that the adsorption selectivity was subject to the surface elemental composition of the fiber coatings.The cobalt and nitrogen co-doped carbonaceous coating showed better adsorption selectivity for ultraviolet filters.In contrast,the cobalt-doped carbonaceous coating exhibited higher adsorption selectivity for polycyclic aromatic hydrocarbons.The fabricated fibers present higher mechanical stability and higher adsorption capability for model analytes than the commercial polydimethylsiloxane and polyacrylate fibers.These new strategies will continue to expand the Ni Ti fibers as versatile fiber substrates for metal-organic frameworks(MOFs)-derived coating materials with controllable nanostructures and tunable properties.

Mechanistic Investigation into the Role of Aluminum Diffusion in the Oxidation Behavior of Cryomilled NiCrAlY Bond Coat

High temperature oxidation behavior of the bond coat layer is a critical factor that controls the failure mechanism of thermal barrier coatings（TBCs）.Previous work reveald that TBCs with cryomilled NiCrAlY bond coats exhibited an improved oxidation behavior compared to equivalent TBCs with conventional bond coats.The cryomilled NiCrAlY bond coats contributed to a slower growth rate of thermally grown oxides（TGO） with a final thinner thickness and enhanced homogeneity in TGO composition.To better understand the improved oxidation behavior,a mechanistic investigation based on diffusion theory and quantum mechanics is performed to elucidate the role of aluminum diffusion in the oxidation behavior and how the microstructural features of the cryomilled NiCrAlY bond coats,i e,the creation of a thermally stable,uniform distribution of ultrafine Al-rich oxide dispersoids,affect the diffusion kinetics of Al and the migration of free electrons.It is revealed that these Al-rich oxide dispersoids result in a uniform diffusion of Al and slow migration of free electrons within the NiCrAlY bond coat,consequently leading to the improved oxidation behavior.

碳钢表面电镀锌镍/有机富铝复合涂层的制备与性能

为提高碳钢表面电镀锌镍的防护性能和应用限制,采用电镀锌镍层作为底层,有机富铝涂层作为顶层,设计出一种复合涂层防护体系。采用扫描电镜(SEM)、能谱(EDS)、中性盐雾试验、电化学测试等手段对电镀锌镍/有机富铝复合涂层的表面/截面形貌及耐蚀性进行表征与分析。结果表明:电镀锌镍/有机富铝复合涂层表面光滑平整,无明显缺陷,复合涂层体系界面结合良好,无分层现象,经1500 h中性盐雾试验后复合涂层无红锈。复合涂层较单独的电镀锌镍合金层腐蚀电流密度降低了2个数量级,表现出受控的牺牲阳级作用,并实现了在海洋防护领域的应用。复合涂层有效提升了电镀锌镍层的耐腐蚀性能,拓宽了电镀锌镍层在腐蚀防护领域的应用范围。

Low-temperature Formation of Aluminide Coatings on Ni-base Superalloys by Pack Cementation Process

This article investigates the low-temperature formation of aluminide coatings on a Ni-base superalloy by pack cementation process. The pack cemented coatings characteristic of high density and homogeneity possess a two-layer structure. The top layer mainly consists of Al3Ni2 and Al3Ni,while the bottom layer of Al3Ni2. Great efforts are made to elucidate the effects of different experimental parameters on the microstructure and the constituent distribution of the coatings. The results show that all the parameters exclusive of the pack activator （NH4Cl） content produce effect on the coating thickness,but do not on the microstructure and the constituent distribution. The pack activator （NH4Cl） content affects neither the coating thickness nor structure and constituent distribution. The parabolic relationship between the coating thickness and the deposition time suggests that the process is diffusion-controlled. Furthermore,the article demonstrates a linear relationship between the coating thickness and the re-ciprocal deposition temperature.

压延铜箔的无氰电镀镍铜黑化处理工艺

为了研究出相较于电镀纯镍黑化工艺成本更低的电镀镍铜黑化工艺,以NiSO_(4)·6H_(2)O、CuSO_(4)·5H_(2)O、H_(3)BO_(3)、(NH_(4))_(2)S_(2)O_(8)和C_(6)H_(15)NO_(3)为镀液基本成分,通过加入添加剂,使金属在铜箔表面沉积形成光陷阱结构,从而实现电镀镍铜使铜箔黑化的目的。研究了镀液成分及工艺参数对黑化箔镀层亮度的影响,对黑化箔镀层的成分进行了测试,并对黑化箔镀层结构进行了观察分析。研究结果表明:电镀镍铜的黑化箔镀层中Cu代替Ni形成镀层,黑化箔镀层成分为NiCu;通过加入添加剂可以使电镀时使用的电流密度降低,达到了降低成本的目的。

Cr30钢表面镍包WC增强铁基合金涂层的微观组织和耐磨耐蚀性能研究

为改善Cr30钢表面的耐冲蚀磨损性能以及耐硫酸、盐酸腐蚀性能,以铁合金粉和镍包WC颗粒的混合物为原料,采用激光熔覆技术在Cr30钢表面制备含镍包WC铁基合金涂层,研究了原料中镍包WC质量分数(10%~30%)对铁基合金涂层的显微组织、物相组成、显微硬度、耐冲蚀磨损性能、耐硫酸和盐酸腐蚀性能的影响。结果表明:不含镍包WC的铁基合金涂层物相为FeCr固溶体和Cr_(23)C_(6);含10%和20%镍包WC的铁基合金涂层物相为FeCr固溶体、Cr_(23)C_(6)和Fe3W3C;随着镍包WC含量增至30%,铁基合金涂层中析出了新的碳化物Fe_(6)W_(6)C,含30%镍包WC的铁基合金涂层物相为FeCr固溶体、Cr_(23)C_(6)、F_(e)3W_(3)C和Fe_(6)W_(6)C。随着镍包WC含量的增加,铁基合金涂层的显微硬度、耐冲蚀磨损和耐硫酸、盐酸腐蚀性能提高,当镍包WC质量分数为30%时,铁基合金涂层的组织致密、细化效果最明显,涂层的硬度最高,达到786 HV_(0.5);30%镍包WC的铁基合金涂层的耐冲蚀磨损、耐硫酸和盐酸腐蚀性能最佳。