As-plated Condition Research Articles

Improved fatigue strength of Cr-electroplated 7075-T6 Al alloy by micro-shot peening

The effects of micro-shot peening (MSP) on the rotating bending fatigue resistance of Cr-electroplated AA 7075-T6 Al alloy were investigated. Fe-based amorphous particles with sizes of 50–80 μm were used as the shot balls and peened under 100 % surface coverage. The shot-peen intensity, determined by the height of the N-type Almen specimen, was 0.110 mm. The Cr-electroplated layer consisted of a network of microcracks in the as-plated condition. Without the necessity of micro-crack initiation, the Cr-electroplated substrate had the shortest fatigue life and lowest fatigue strength among the tested samples. MSP significantly increased the fatigue strength/life of 7075-T6 Al alloy with or without Cr-plating. The introduction of high residual compressive stress combined with the formation of a nanograined structure in the MSP zone was responsible for the high resistance to fatigue crack growth of the MSP sample.

A comparative study on morphological, mechanical and tribological properties of electroless NiP, NiB and NiBP coatings

The aim of this paper is to fabricate the NiBP polyalloys coatings by electroless coating technique on the aluminum substrate. A comparative investigation of morphological and hardness properties between NiP, NiB and NiBP coatings is employed. Also, the effect of heat treatment process on the nanoindentation behaviors of the electroless nickel-based alloys is studied. The highest hardness of 8.76 GPa and Young's modulus of 180.36 GPa were obtained electroless NiBP coatings in the case of as-plated conditions. After heat treatment process at 400°C in an inert atmosphere, electroless NiB coatings showed the highest hardness value of 10.02 GPa and Young's modulus of 207.48 GPa when compared with NiP and NiBP coatings. Although electroless NiB coatings exhibited the highest Young's modulus and harness value, electroless NiBP coatings showed the best protection against wear in all loads of 1, 2 and 3N and all sliding velocities of 100, 200 and 400 mm/s due to showing H/E ratio of NiBP coatings comparing with NiB and NiP coatings.

Optimizing Heat Treatment for Electroplated NiP and NiP/SiC Coatings

NiP (P > 10 wt.%) coatings are amorphous coatings whose structure can be transformed by heat treatment into a crystalline structure and hardened by precipitation of Ni3P. In this study, NiP coatings and composite ones with SiC nanoparticles were produced by electrodeposition, and their structural transformation by heat treatment was studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The microhardness and the scratch and corrosion resistance of the coatings were evaluated and compared before and after different heat treatments. The results showed that in as-plated condition, the addition of SiC particles in the coatings did not modify the microstructure, microhardness, or electrochemical behavior. However, the SiC particles’ role was disclosed in combination with heat treatment. Composite coatings that were heat treated at 300 °C had higher microhardness and scratch resistance than the pure NiP one. In addition, composite coatings maintained their scratch resistance up to 400 °C, while in the case of the NiP ones, there was a reduction in scratch resistance by heating at 400 °C. It was also concluded that heating temperature has the main role in hardness and corrosion resistance of NiP and composite coatings, rather than heating time. The optimum heat-treatment protocol was found to be heating at 360 °C for 2 h, which resulted in a maximum microhardness of about 1500 HV0.02 for NiP and its composite coating without sacrificing the corrosion resistance.

Tribological evaluation of electroless Ni–B coating on metal-working tool steel

The aim of this research is to evaluate the tribological characteristics of the electroless Ni–B film under extreme pressure conditions, with coating thickness of 3 μm, 6 μm, and 12 μm in the as-plated condition and with incorporation of heat treatment (HT) (200 °C by 90 min). An electroless method is employed for Ni–B coating deposition on D2 tool steel specimens. A synthetic fluid was used as a lubricant, with a water–oil ratio of 10:1. Tribological evaluations were performed on a block-on-ring configuration according to ITEePib Polish method for testing lubricants under conditions of scuffing. Results indicate that electroless technology improved the coefficient of friction (COF) of the tool steel, ranging from 15 to 30%, with 3 μm to 12 μm of coating, respectively. This enhancement was increased by applying a heat treatment to the coated components, showing improvements of 24–38% with 3 mm to 12 mm, respectively. It is also observed that wear of the evaluated coupons also showed improvements ranging from 35 to 60%. These results demonstrate the potential of an electroless technique on materials suitable for metal-forming tooling and components, while decreasing friction and wear of mechanical components.

Comparative study on the friction-wear property of As-plated, Nd-YAG laser treated, and heat treated electroless Nickel-Phosphorus/Crab shell particle composite coatings on mild steel

Nickel-Phosphorus/Crab shell particle (NiP/CSP) composite coatings were prepared with different weight dispersions of CSP (0.5 g/l, 1.0 g/l, 1.5 g/l, 2.0 g/l, 2.5 g/l and 3.0 g/l) on mild steel using electroless coating process. Fabricated coatings were post treated with heat treatment and Nd:YAG laser treatment process and followed by a comparative study on surface morphology, surface hardness, phase structure, and friction-wear property with as-plated NiP and NiP/CSP composite coatings. The result showed the relative changes in the surface morphology of NiP/CSP composite coatings after Nd:YAG laser treatment. Dendrite structure was observed for laser treated coatings and its formation was affected by the incorporation of CSP in the NiP matrix. FeNi2P phase was formed for laser treated coatings in addition to the Ni3P and Ni12P5 phases. Higher surface hardness of 966 Hv0.05 and 941 Hv0.05 was achieved for laser treated NiP and NiP/CSP composite coatings compared to the heat treatment process and as-plated condition. On comparison with various weight dispersions, higher surface hardness of 941 Hv0.05 was obtained for NiP/CSP (2.5 g/l) composite coatings as a result of the high diffusion of Fe element from substrate to the surface. Low friction coefficient was seen for the heat treatment process followed by the as-plated and laser treatment process. The formation of FeNi2P phase caused an increase in the friction coefficient for laser treated NiP and NiP/CSP composite coatings. However, there was an improvement in the wear resistance of laser treated coatings compared to the as-plated and heat treated coatings.

Effect of SiC particle size and heat-treatment on microhardness and corrosion resistance of NiP electrodeposited coatings

Electrodeposition of NiP composite coatings with nano and sub-micron sized SiC has been carried out to investigate the possibility of replacing hard chromium coatings. The composition and structure of the coatings were evaluated by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis, respectively. Microhardness was measured by Vickers indentation and polarization measurements were carried out to study the corrosion behavior of the coatings. The results showed that submicron particles can be codeposited with a higher content as compared to nano sized ones. However, even if a smaller amount of the nano-sized SiC particles are incorporated in the coating, the contribution to an increasing microhardness was comparable with the submicron sized particles, which can be related to the higher density of codeposited particles. SiC particles did not change the anodic polarization behavior of NiP coatings in a 3.5% NaCl solution. Finally, the effect of heat-treatment on the coatings properties at 400 °C for 1 h was studied to investigate the contribution of particles and heat-treatment on hardness and corrosion properties. It was found that the heat-treatment doubled the microhardness and changed the anodic polarization behavior of the coatings from passive to active with respect to the as-plated conditions.

Characterization of microstructure and properties of electroless duplex Ni-W-P/Ni-P nano-ZrO2 composite coating

In this study, we prepared the Ni-W-P/Ni-P nano-ZrO2 nanocomposite coating by electroless chemical deposition methods. The structures, morphologies, and corrosion behavior of the nanoparticle enhanced duplex coating were evaluated by X-ray diffraction, atomic force microscopy, scanning electron microscopy as well as the electrochemical methods, such as the potentiodynamic polarization curve and electrochemical impedance spectroscopy. The Ni-W-P/Ni-P nano-ZrO2 duplex coatings were amorphous under the as-plated condition and crystallized and produced nickel borides upon heat-treatment. The duplex coatings exhibit the higher microhardness after different heat treatments and also depict the better corrosion resistance than conventional Ni-P coating in the H2S/CO2-containing environment. This novel type of Ni-P coating possesses both excellent mechanical properties and good corrosion resistance, and it would expand their scope of applications in H2S/CO2-containing environment.

Influence of the Tungsten Content on Surface Properties of Electroless Ni-W-P Coatings

Ternary Ni-W-P films were produced by electroless deposition using baths with different tungsten concentrations. After deposition, the coated surfaces were annealed at 400°C for 1h. Surface morphology and film composition in the as-plated condition were assessed by SEM and EDS analyses, respectively. The crystalline phases after annealing were investigated by X-ray diffraction (XRD). Nanoindentation tests were performed to assess the mechanical properties of the deposited films. Surface roughness was determined by confocal laser scanning microscopy (CLSM). Friction coefficient was evaluated by reciprocating were tests in a nanotribometer. The corrosion behavior was evaluated by potentiodynamic polarization curves. The results showed that the surface morphology, crystallization behavior and corrosion resistance were affected by the tungsten content in the film. The best corrosion performance was obtained for the ternary films after annealing. Hardness, surface roughness and friction coefficient were dependent of the tungsten concentration in the film.

Effect of Operating Temperature on Tribological Behavior of As-Plated Ni-B Coating Deposited by Electroless Method

ABSTRACTThe present work investigates the tribological behavior of electroless Ni-B coating in its as-plated condition at elevated operating temperatures. Ni-B coating is deposited using an electroless method on AISI 1040 steel specimens. Coating characterization is done using scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction techniques. Vicker's microhardness and surface roughness are measured. Friction and wear tests are carried out on a pin-on-disc tribological test setup at room and elevated temperatures of 100, 300, and 500°C. The tribological behavior deteriorates at 100°C compared to room temperature. Electroless Ni-B coating shows excellent wear resistance at 300°C, which again degrades at 500°C due to severe oxidation and softening of the deposits. The worn surface of the coatings is analyzed using optical microscopy and scanning electron microscopy. Within the temperature range considered, the wear mechanism changes from adhesion to a combination of adhesion and abrasion as the temperature rises from ambient condition to 100°C, following which the wear mechanism is predominantly abrasive. The formation of a tribochemical oxide film also affects the tribological behavior of the coatings at high temperature.

Electroless Nickel Plating – A Review

The operating process, versatility and the increasing research interest in optimising the process and products technology in the electroless plating method of metal coating, particularly, the electroless nickel plating of metallic substrates such as mild steel, necessitates the writing of this review. It is also aimed at providing more literature information, both of the past and the present published research in this field. In this paper, electroless nickel plating is introduced. The various nickel plating solutions and baths’ operating parameters; main types of electroless nickel plating; the mechanism involved in the plating process; application of the nickel plating process to iron powders; advantages and disadvantages and the process’s other applications are reviewed. Electroless nickel plating produces an amorphous deposit in the as-plated condition. The deposit is not dependent on current distribution and hence it is almost uniform in thickness. Electroless nickel plating is far more difficult to remove chemically than conventional nickel deposits due to its superior corrosion resistance. The deposit has a good wettability and is generally hard. However, its bath control is more complex than with electroplating. The bath also has lower efficiency and higher operating costs, even without the use of electricity.

EFFECT OF ANNEALING TEMPERATURE ON HARDNESS AND WEAR RESISTANCE OF ELECTROLESSNi–B–MoCOATINGS

Formation of nickel–boron–molybdenum ( Ni – B – Mo ) coating on steel by electroless plating and evaluation of their morphology, hardness and tribological properties post heat treatment at different temperatures for 1 h is investigated. The 25 μm thick coating is uniform and adhesion between the substrate and coating is good. Ni – B – Mo coating was amorphous-like structure in their as-plated condition and by 400°C heat-treated coating, nickel fully crystallized and nickel borides and molybdenum carbide were formed. All coatings exhibited higher hardness than the substrate steel. Hardness values of all coatings up to 400°C did not change distinctively but decreased partly beyond 400°C. Friction coefficient reached lowest value post heat treatment at 300°C but later increased with increasing tempering temperature. Wear resistance was lowest in as-plated coating; however it reached the highest value at 300°C. Worn surface of the coatings showed the abrasive wear as the dominant wear mechanism. An additional adhesive wear mechanism was detected in coating tempered at 550°C. Moreover, our results confirmed that the molybdenum addition improved the thermal stability of the resulting coating. Therefore, Ni – B – Mo coating has potential for application in precision mould, optical parts mould or bipolar plates, where thermal stability is essential.

Effect of Annealing Temperature on the Corrosion Resistance of Electroless Ni-B-Mo Coatings

The Ni-B-Mo coating on steel by electroless plating and the evaluation of the morphology and corrosion performance after applying heat treatments at different temperatures for 1 h were investigated in this study. The 25-μm-thick coating was uniform and adhesion between the substrate and the coating was good. The coating consisted of an amorphous-like structure in their as-plated condition, and after annealing at 400 °C for 1 h, crystallized nickel, nickel borides, and molybdenum carbide were formed. Immersion tests in 10% HCl solution and potentiodynamic polarization measurements in 3.5% NaCl aqueous solution were applied to investigate corrosion resistance. The corrosion performance of heat-treated coatings was compared with steel and the as-plated coating. By increasing the annealing temperature, corrosion potential shifted toward a noble direction, corrosion current density decreased and the weight loss of specimens decreased, demonstrating an increase in corrosion resistance. Best corrosion performance was achieved by the coating heat treated at 550 °C .

Fabrications of Electroless Ni-P Composite Coatings before and after Annealing and Tribological Analyses

In the present study, SiC reinforced particles were introduced to the Ni-P plating bath, and developed high SiC content composite coatings. Thin films nature properties and mechanical performances were evaluated well. The results showed that the Ni-P alloy embedded SiC particles formed a few cavities, and reduced coatings hardness and wear resistance in as-plated condition. After 400°C heat-treatment, Ni3P crystalline phase formed and reached the max hardness, and conducted excellent trybological performances. SiC particles were decoposited in 600°C and reacted with Ni to form Ni3Si and Ni5Si2, caused the decreasing in hardness.

Electroless Ni-P/Ni-B-B4C duplex composite coatings for improving the corrosion and tribological behavior of Ck45 steel

Ni-P/Ni-B-B4C duplex composite coatings were deposited on Ck45 by electroless plating process, and their structure, morphology, micro hardness and corrosion resistance were evaluated. The duplex coatings were prepared using dual baths (acidic hypophosphite- and alkaline borohydride-reduced electroless nickel baths) with Ni-P as the inner layer. The coatings were amorphous in as-plated condition and nanocrystallized, and produced nickel borides upon heat-treatment. SEM observations showed that the duplex interface on the Ck45 was uniform, and the compatibility between the layers was good. The Ni-P/Ni-B-B4C coating’s microhardness and corrosion resistance of Ni-B-B4C coating as the outer layer were higher than Ni-P coatings. The Ni-P/Ni-B-B4C duplex composite coatings with high hardness and good corrosion resistance properties would expand their scope of applications.

Heat Treated and As-Plated Electroless Duplex Ni-P/Ni-B Coatings: Evaluation of Hardness and Wear Resistance

The present work deals with the formation of NiP/NiB duplex coatings by electroless plating and evaluation of their hardness and wear resistance. The duplex coatings were prepared with Ni-P as the inner layer. To analyze the structure of the coatings, XRD analysis was carried out. According to the results, NiP and NiB coatings are amorphous in their as-plated condition and after applying heat-treatment at 450 °C for 1 h, both NiP and NiB coatings crystallize and produce nickel, nickel phosphide and nickel borides in the coatings. To determine the surface morphology and cross-section characteristics of the coatings, SEM observations were carried out and concluded that duplex coatings are uniform and good coherent exists between the duplex layers and the coatings are also connected closely to the substrate. The hardness of electroless nickel duplex coatings increased with applying heat treatment and reached maximum value at coatings annealed at 400 °C. To analyze the tribological properties, pin-on-disc tests were carried out. The wear track patterns on the coatings and on Al2O3balls were then examined by optical microscopy and EDS. The friction coefficient and wear rate of the coatings were lower than the substrate steel. Friction coefficient decreased from 0.43 to 0.36 and wear resistance decreased from 11.3 to 6.4 by applying heat treatment at 450 °C for 1 h to duplex coatings.

Effect of Annealing Temperature on the Corrosion Resistance of Electroless Produced Ni-B-W Coatings

The present work deals with the formation of Ni-B-W coating on steel by electroless plating process and evaluation of their corrosion resistance after applying heat treatments at different temperatures for 1 h. The Ni-B-W coating was prepared using alkaline borohydride- reduced electroless nickel bath. Scanning electron microscopy of the surface cross-sectional view of the electroless Ni-B-W coating was analyzed and layer characteristics was investigated. Coating structure was investigated using XRD. The study reveals that the Ni-B-W coating is amorphous in their as-plated condition and upon heat treatment at 400 0C for 1 h, Ni-B-W coating crystallize and produce nickel and nickel borides in the coatings. Annealing temperature dependence of the corrosion resistance of the coating was investigated by potentiodynamic polarisation measurements. These results show that the Ni–B-W coating annealed at 650 0C exhibit better corrosion resistance than those of coatings with other annealing temperature. The corrosion resistance increased after the crystallisation of the coating, due to factors like; decrease of porosity and internal stress and the formation of tungsten oxide on the surface acting as a protective layer.

Electroless Ni-B-Si3N4 Composite Coating: Deposition and Evaluation of Its Characteristic Properties

Deposition of electroless (EL) Ni-B-Si3N4 composite coating and its characteristic properties are addressed.Hydrogen evolution limits the level of incorporation of Si3N4 particles in the EL Ni-B matrix to 2 wt%. Incorporation Si3N4 particles increased the surface roughness of the matrix but did not influence its structure. The microhardness of EL Ni-B-Si3N4 composite coating in its as-plated condition is 632 ± 17 HV0.1. Heat treatment at 350 and 450°C for 1 h increased its hardness. Adhesive wear is the predominant wear mechanism of EL Ni-B-Si3N4 composite coating. Its corrosion protective ability did not differ much with its plain counterpart.

Preparation and characterization of electroless Ni-Fe-P alloy films on fly ash cenospheres

The process of depositing Ni-Fe-P alloy films on fly ash cenospheres (FACs) through modified electroless plating is documented. A coupling procedure was used with γ-aminopropyltriethoxy silane (APS) as coupling agent and silver nitrate as activator. The resultant Ni-Fe-P/FACs composites were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and vibrating sample magnetometry (VSM). The results show that continuous and uniform films of Ni-Fe-P alloy were obtained on the surfaces of the FACs. DSC traces indicated that two distinct exothermic peaks appeared during the heat treatment, which moved to higher temperature with decrease in mole ratios of Ni2+/Fe2+ in the coating. XRD spectra confirmed that electroless Ni-Fe-P alloy deposits were amorphous in the as-plated condition, which transformed from the amorphous to crystalline phase with increase in calcining temperature. In addition, VSM data revealed that the resulting sample exhibited characteristics of soft magnetic materials at room temperature. The magnetic performances of the composites would be ameliorated with an increase in iron content in the coating and calcining temperature.

Influence of deposition temperature and heat treatment on the performance of electroless Ni–B films

Electroless nickel–boron (Ni–B) was synthesized on mild steel or copper surface. The deposition of thin electroless Ni–B films using an acidic bath having nickel chloride as a source of nickel and dimethylamine borane (DMAB) as a reducing agent and operated at low temperature has been investigated in this paper. The effect of the plating time and temperature on the quality of Ni–B coatings was estimated. The results revealed that the plating rate decreases with increasing plating time and increases with increasing plating temperatures. The boron (B) content of the electroless Ni–B layer increased with increasing temperature. The resulting surfaces were examined and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). XRD analysis was performed to investigate structural modifications. Microhardness, corrosion and oxidation resistance of electroless as-plated and heat-treated Ni–B coatings, were evaluated. The effect of heat treatment temperature on the phase structure and microhardness of Ni–B coated at different temperatures was discussed. XRD patterns reveal that electroless Ni–B coatings deposited at 60 and 80°C are amorphous in as-plated condition and undergo phase transformation to crystalline nickel and nickel borides upon heat-treatment. Heat treatment achieved significant improvement in the microhardness and corrosion resistance due to the formation of the Ni–B compound phases (Ni3B).

Electroless Ni-P/Ni-B duplex coatings for improving the hardness and the corrosion resistance of AZ91D magnesium alloy

The Ni-P/Ni-B duplex coatings were deposited on AZ91D magnesium alloy by electroless plating process and their structure, morphology, microhardness and corrosion resistance were evaluated. The duplex coatings were prepared using dual baths (acidic hypophosphite- and alkaline borohydride-reduced electroless nickel baths) with Ni-P as the inner layer. The coatings were amorphous in as-plated condition and crystallized and produced nickel borides upon heat-treatment. SEM observations showed that the duplex interface on the magnesium alloy was uniform and the compatibility between the layers was good. The Ni-P/Ni-B coatings microhardness and corrosion resistance of having Ni-B coating as the outer layer was higher than Ni-P coatings. The Ni-P/Ni-B duplex coatings on AZ91D magnesium alloy with high hardness and good corrosion resistance properties would expand their scope of applications.