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.

Tribological Behaviors of Electroless Nickel-Boron Coating on Titanium Alloy Surface

Titanium alloys are excellent structural materials in engineering fields,but their poor tribological properties limit their further applications.Electroless plating is an effective method to enhance the tribological performance of alloys,but it is difficult to efficiently apply to titanium alloys,due to titanium alloy’s strong chemical activity.In this work,the electroless Nickel-Boron(Ni-B)coating was successfully deposited on the surface of titanium alloy(Ti-6AL-4V)via a new pre-treatment process.Then,linearly reciprocating sliding wear tests were performed to evaluate the tribological behaviors of titanium alloy and its electroless Ni-B coatings.It was found that the Ni-B coatings can decrease the wear rate of the titanium alloy from 19.89×10^(−3)mm^(3)to 0.41×10^(−3)mm^(3),which attributes to the much higher hardness of Ni-B coatings.After heat treatment,the hardness of Ni-B coating further increases corresponding to coating crystallization and hard phase formation.However,heat treatment does not improve the tribological performance of Ni-B coating,due to the fact that higher brittleness and more severe oxidative wear exacerbate the damage of heat-treated coatings.Furthermore,the Ni-B coatings heat-treated both in air and nitrogen almost present the same tribological performance.The finding of this work on electroless coating would further extend the practical applications of titanium alloys in the engineering fields.

Quality of Electroless Ni-P (Nickel-Phosphorus) Coatings Applied in Oil Production Equipment with Salinity

The corrosion resistance of nickel-phosphorus (Ni-P) coatings and their mechanical properties in seawater have led inestigations into the development of new technologies and the replacement of some special alloys in equipment used in oil production, such as valves, tubing, sucker rod joints, pumps, riser, manifolds and subsea Christmas trees. These studies began with Brenner and Riddel who developed, in the 1940s, formulations for Ni-P deposition on carbon steel without using an electric current. Joint deposition of nickel and phosphorus on a metallic surface (carbon steel) without applying an external current is accomplished using cathodic reduction with hydrogen (H) from a reducing agent (sodium hypophosphite) and nickel salts. To assure good performance of a Ni-P coating, the deposit quality must be inspected and evaluated during the chemical deposition process or in the end product. The recommended test parameters are: thickness, layer uniformity, hardness, adhesion, porosity, corrosion resistance and chemical composition of the nickel-phosphorus coating. The purpose of this paper was to investigate the Ni-P coating process, to evaluate the b?haviour of Ni-P in a saline environment using aqueous brine (3.5% - 30% sodium chloride by mass) and to present possible defects that could compromise the coating.

Effect of wear conditions on tribological properties of electrolessly-deposited Ni-P-Gr-SiC hybrid composite coating

The friction and wear properties of the electrolessly-deposited Ni-P-Gr-SiC composites were investigated. The effects of graphite content, load and rotation speed on the friction coefficient and wear resistance of the composite coatings were mainly investigated. The worn surface and cross section of the coatings were characterized by scanning electron microscopy and energy-dispersive X-ray analysis. The results show that the composite coatings reveal good antifriction and wear resistance due to the synergic effect of graphite and SiC particles. The formation of graphite-rich mechanically mixed layer （GRMML） on the surface of Ni-P-Gr-SiC coating contributes to the good tribological behavior of the wear counterparts and SiC particles play a load bearing role in protecting GRMML from shearing easily.

Characteristics of microstructure and performance of laser-treated electroless Ni-P/Ni-W-P duplex coatings

Characteristics of microstructures of electroless Ni-P/Ni-W-P duplex coatings were investigated using SEM/EDX and XRD analysis techniques. Microhardness and wear behaviour of the coatings before and after laser crystallization were evaluated by measurements of hardnesses of coating surface and cross-section, and by unlubricated friction and wear experiments. The results indicate that it is possible to prepare electroless Ni-P/Ni-W-P duplex coatings by sequential immersion in two different plating baths. After laser crystallization, the microstructures of electroless Ni-P/Ni-W-P duplex coatings present the characteristics of higher degree of crystallization and larger grain size for outer layer Ni-W-P than inner Ni-P, but outer layer has a higher hardness. The wear resistance of laser-treated duplex coatings in a given process parameter conditions is superior to the as-plated ones. Laser treatment was performed directly in air without argon protection, which provides the possibility for application of industrialized production.

Mechanical assisted electroless barrel-plating Ni-P coatings on magnesium alloy

A mechanically assisted electroless barrel-plating Ni-P was carried out in a rolling drum containing Mg alloy specimens and ceramic balls, which was submerged in a bath containing electroless plating solution deposited by this novel technique have a It is demonstrated that the Ni-P coatings crystallized Ni-P solid solution structure, showing fine-grains, higher hardness, and higher corrosion resistance compared with the conventional electroless plated amorphous Ni-P coatings. After heat treatment at 400 ℃ for 1 h, the structure of such Ni-P coatings were transformed to a structure with Ni-Ni3P double phases, and cracks in these coatings could not be observed, whereas cracks appeared seriously in the conventional electroless plated Ni-P coating after same heat treatment. Therefore, both hardness and corrosion resistance of these Ni-P coatings can be improved further by heat treatment. All of these beneficial effects can be attributed to the role of mechanical attrition during the mechanically assisted electroless barrel-plating process.

Amorphous Co-B/Al nanocomposites prepared by electroless coating technique and their excellent catalytic activity

To improve the catalytic activity of amorphous Co-B alloys, Co-B coated aluminum （Co-B/M） nanocomposites were prepared by electroless coating technique and evaluated as additives for the catalytic performance of ammonium perchlorate （AP） and AP-based solid state propellants. X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, inductive coupled plasma emission spectrometry （ICP）, differential scanning calorimetry （DSC） as well as strand burner method were employed to characterize the crystal phase, morphologies, chemical composition, and catalytic activity of the as-synthesized material. The results show that a continuous layer of about 100 nm amorphous Co72.6B27.4 covers the surfaces of M particles. Addition of the as-synthesized Co-B/A1 nanocomposites as catalysts promotes AP decomposition, enhances the burning rate, and lowers the pressure exponent of the AP-based propellants considerably.

Preparation and Tribological Properties of Ni-P Electroless Composite Coating Containing Potassium Titanate Whisker

Nickel-phosphorus （Ni-P） composite coatings containing potassium titanate （K2Ti6O13） whiskers （PTWs） were prepared by electroless plating. The surface morphology and component of coatings were investigated by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDX）, respectively before and after wear test. The tribological performance was evaluated using a pin-on-disk wear tester under dry conditions. It is found that the Ni-P-PTWs composite coatings exhibit higher wear resistance than Ni-P and Ni-P-SiC electroless coatings. The favorable effects of PTWs on the tribological properties of the composite coatings are attributed to the super-strong mechanical properties and the specific tunneling structures of PTWs. The PTWs greatly reinforce the structure of the Ni-P-based composite coatings and thereby greatly reduce the adhesive and plough wear of Ni-P-PTWs composite coatings.

Comparative study of microstructure and corrosion resistance of electroless Ni-W-P coatings treated by laser and furnace-annealing

A comparative study of amorphous electroless Ni-W-P coatings on mild steel substrate treated by a high power diode laser and furnace annealing was presented.Effects of different laser operating parameters and furnace-annealing conditions on microstructures,in terms of crystallisation,pores formation and grain growth,were investigated using SEM/EDX and XRD. Corrosion behaviours of these coatings before and after various treatments were evaluated with anodic polarisation in 0.5 mol/L H2SO4 solution.The results show that the furnace-annealing produces either a mixture of nanocrystallined Ni and amorphous phases or precipitated Ni3P phase distributed in nanocrystallined Ni-based matrix,depending on annealing temperatures,whilst the laser treatment under the operating conditions only produces nanocrystallined Ni-based matrix with Ni3P precipitates.Corrosion performance of the coatings treated by both the laser and the furnace-annealing is dependent on the annealing temperature and laser operating conditions.Corrosion mechanisms of various treated-coatings were discussed in the consideration of phase constitutes and proportion,grain sizes of both Ni and Ni3P phases,pores formation and residual stresses.

Preparation and characterization of molybdenum powders with copper coating by the electroless plating technique

Molybdenum powders with a diameter of approximately 3 μn were coated with copper using the electroless plating technique in the pH 12.5-13 and temperature range of 55-75℃. The optimization of the electroless copper bath was evaluated through the combination of process parameters like pH and temperature. The optimized values ofpH and temperature were found to be 12.5 and 60℃, respectively, which attributes to the bright maroon color of the coating with an increase in weight of 46%. The uncoated and coated powders were subjected to microstructural studies using scanning electron microscope （SEM） and the phases were analyzed using X-my diffrction （XRD）. An attempt was made to understand the growth mechanism of the coating. The diffusion-shrinkage autocatalytic model was suggested for copper growth on the molybdenum surface.

Wear and Corrosion Resistance of Electroless Plating Ni-P Coating on P110 Steel

In order to improve the surface performance and increase the lifetime of P 110 oil casing tube steel during operation, electroless plating was conducted to form Ni-P coating onto its surface. The surface morphology/element distribution and phase constitution of the Ni-P coating were analyzed using scanning electron microscope （SEM） equipped with energy dispersive spectrometry （EDS） and X-ray diffraction （XRD）. Tribological and electrochemical measurement tests were applied to investigate the wear and corrosion resistance of P110 steel and the Ni-P coating. The results showed that a uniform and compact, high phosphorous Ni-P coating was formed. The obtained Ni-P coating indicated certain friction-reduction effect and lower mass loss during friction-wear tests. The Ni-P coating also exhibited higher corrosion resistance in comparison with bared P 110 steel. The obtained N i-P coating has significantly improved the surface performance of P110 steel.

PROCESS AND PROPERTIES OF ELECTROLESS PLATING RE-Ni-B-SiC COMPOSITE COATINGS

Technology and properties of electroless composite RE-Ni-B-SiC coatings have been investigated.Results show that stabilizer plys a decisive role in electroless composite Ni-B-SiC,the addition of appropriate quantity of RE(rare earth) into the Ni-B-SiC bath not only increases SiC content in composite coatings,their hardness and wear resistance but also improves crystalline fineness,Wear resistance increases with the increase of SiC.Hardness and wear resistance of composite coatings reach peak values a fter heat treatment at 4OO and 500℃ for 1h respectively.

Microstructure and electrical conductivity of electroless copper plating layer on magnesium alloy micro-arc oxidation coating

In order to impart electrical conductivity to the magnesium alloy micro-arc oxidation(MAO)coating,the electroless copper plating was performed.Effects of plating temperature and complexing agent concentration on the properties of the electroless copper plating layers were studied by measuring their microstructure,corrosion resistance and electrical conductivity.It was found that the optimized plating temperature was 60°C,and the most suitable value of the complexing agent concentration was 30 g/L.Under this condition,a complete and dense plating layer could be obtained.The formation mechanism of the plating layer on magnesium alloy MAO coating was analyzed.A three-stage model of the plating process was proposed.The square resistance of the plated specimen was finally reduced to 0.03Ω/□after the third stage.Through electroless copper plating,the MAO coated sample obtained excellent electrical conductivity without significantly reducing its corrosion resistance.

Evaluation of residual stress and corrosion behaviour of electroless plated Ni-P/Ni-Mo-P coatings

Single Ni-P and Ni-Mo-P coatings as well as duplex Ni-P/Ni-Mo-P coatings with the same compositions were prepared by electroless plating.The residual stresses of the coatings on the surface and cross sections were measured by nanoindentation and AFM analysis,and the corrosion behaviour of the coatings in10%HCl solution was evaluated by electrochemical methods,to establish the correlation between the residual stresses and corrosion behaviour of the coatings.The results showed that the single Ni-P and duplex Ni-P/Ni-Mo-P coatings presented residual compressive stresses of241and206MPa respectively,while the single Ni-Mo-P coating exhibited a residual tensile stress of257MPa.The residual compressive stress impeded the growth of the pre-existing porosity in the coatings,protecting the integrity of the coating.The duplex Ni-P/Ni-Mo-P coatings had better corrosion resistance than their respective single coating.In addition,the stress states affect the corrosive form of coatings.

Preparation of Core-shell Cu-Ag Bimetallic Powder via Electroless Coating

A novel method of electroless silver coating on copper powders was reported, in which hydrazine was used as the reducing agent, and had some advantages such was used as inhibiting the substitution reaction and reducing consumption of copper powders. In the processes of sensitization and activation, AgNO3 replaces the conventional PdCl2, which solves the impurity of bath. Oxide film on the surface of copper powders was tested by chemical analysis. Ag element tested by XRD and XRF is in the form of Ago and exists on the surface of copper powders, which acts as catalyzer in reduction reaction. Morphology and composition of the coating were characterized by SEM and XRD respectively.

Effects of zincate treatment on adhesion of electroless Ni-P coating onto various aluminum alloys

The effects of alloying elements on zincate treatment and adhesion of electroless Ni-P coating onto various aluminum alloy substrates were examined.Surface morphology of zinc deposits in the 1st zincate treatment and its adhesion were changed depending on the alloying element.The zinc deposits in the 2nd zincate treatment became thinly uniform,and the adhesion between aluminum alloy substrate and Ni-P coating was improved irrespective of the alloying element.XPS analysis revealed the existence of zinc on the surface of each aluminum alloy substrate after the pickling in 5% nitric acid.This zinc on the surface should be an important factor influencing the morphology of zinc deposit at the 2nd zincate treatment and its adhesion.

Studies on electroless Ni-P-Cr_2O_3 and Ni-P-SiO_2 composite coatings

本文对化学镀镍及化学镀镍磷基质中SiO2与Cr2O3的共沉积进行了研究。微粒在不断生长的膜层中共沉积引起了新的化学复合镀层的出现,这些复合镀层许多都具有优异的耐磨及耐蚀性能。通过选取镀层合金/复合微粒/金属基体的组分可改进镀层,获得所需的性能,以满足特别的需求。在对这些复合镀层的应用需求正在迫近与增长的同时,其市场正在迅速扩张。本文开发出了一种合适的复合化学镀镍液,并通过维氏硬度法对化学复合镀镍层进行了表征。采用动电位极化及交流阻抗法测定了镀层的Taber耐磨性能及耐蚀性能。采用SEM及XRD对复合镀层的表面形貌进行了分析。

Erosion and Toughening Mechanisms of Electroless Ni-P-Nano-NiTi Composite Coatings on API X100 Steel under Single Particle Impact

The addition of superelastic NiTi to electroless Ni-P coating has been found to toughen the otherwise brittle coatings in static loading conditions, though its effect on erosion behaviour has not yet been explored. In the present study, spherical WC-Co erodent particles were used in single particle impact testing of Ni-P-nano-NiTi composite coatings on API X100 steel substrates at two average velocities—35 m/s and 52 m/s. Erosion tests were performed at impact angles of 30°, 45°, 60°, and 90°. The effect of NiTi concentration in the coating was also examined. Through examination of the impact craters and material response at various impact conditions, it was found that the presence of superelastic NiTi in the brittle Ni-P matrix hindered the propagation of cracks and provided a barrier to crack growth. The following toughening mechanisms were identified: crack bridging and deflection, micro-cracking, and transformation toughening.

Electroless plating Ni-P matrix composite coating reinforced by carbon nanotubes

Ni-P matrix composite coating reinforced by carbon nanotubes (CNTs) was deposit ed by electroless plating. The most important factors that influence the content of carbon nanotubes in deposits,such as agitation,surfactant and carbon nanot ubes concentration in the plating bath were investigated. The surface morphology,structure and properties of the Ni-P-CNTs coating were examined. It is found that the maximum content of carbon nanotubes in the deposits is independent of carbon nanotubes concentration in the plating bath when it is up to 5 mg/L. The test results show that the carbon nanotubes co-deposited do not change the str ucture of the Ni-P matrix of the composite coating,but greatly increase the ha rdness and wear resistance and decrease the friction coefficient of the Ni-P-C NTs composite coating with increasing content of carbon nanotubes in deposits.

Effect of Addition of Polytetrafluoroethylene (PTFE) and Silicon Carbide (SiC) on Properties of Electroless Nickel Alloy Coatings

Electroless nickel (copper)-phosphorus-silicon carbide (SiC)-polytetrafluoroethylene (PTFE) composite coatings were prepared by adding SiC and PTFE into electroless nickel (copper)-phosphorus alloy baths. The effects of addition of SiC and PTFE on depositing rate, microhardness, wear resistance and anti-friction of the resulted composite coatings were studied. The results indicated that electroless nickel (copper)-phosphorus alloy coatings were greatly improved in depositing rate, microhardness, wear resistance and antifriction by co-deposited proper amount of SiC and PTFE.