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The thermal cycling life of direct bonded aluminum (DBA) and active metal brazing (AMB) substrates with two types of plating—Ni electroplating and Ni–P electroless plating—was evaluated by thermal shock tests between −50 and 250 °C. AMB substrates with Al2O3 and AlN fractured only after 10 cycles, but with Si3N4 ceramic, they retained good thermal stability even beyond 1000 cycles, regardless of the metallization type. The Ni layer on the surviving AMB substrates with Si3N4 was not damaged, while a crack occurred in the Ni–P layer. For DBA substrates, fracture did not occur up to 1000 cycles for all kind of ceramics. On the other hand, the Ni–P layer was roughened and cracked according to the severe deformation of the aluminum layer, while the Ni layer was not damaged after thermal shock tests. In addition, the deformation mechanism of an Al plate on a ceramic substrate was investigated both by microstructural observation and finite element method (FEM) simulation, which confirmed that grain boundary sliding was a key factor in the severe deformation of the Al layer that resulted in the cracking of the Ni–P layer. The fracture suppression in the Ni layer on DBA/AMB substrates can be attributed to its ductility and higher strength compared with those of Ni–P plating.

Electroless nickel–phosphorus (Ni–P) plating is a widely used surface treatment method due to its excellent corrosion and wear resistance properties. However, the inertness of copper to hypophosphite oxidation necessitates a palladium activation process for the preparation of Ni–P coating on copper. In this study, a convenient approach is presented for the deposition of a cobalt layer on copper using galvanic replacement, facilitated by the special complexing ability of iodide. The results demonstrated that the actual potential of copper could be adjusted to be lower than that of cobalt in a solution containing 8 mol L −1 NaI, enabling the deposition of a cobalt layer on copper in 15 min at 90 °C. Furthermore, the deposition rate of the cobalt layer was found to increase with the concentration of CoCl 2 in the NaI solution. Importantly, the Ni–P coating obtained through cobalt layer activation from either acidic or alkaline plating solution exhibited morphology, structure, corrosion resistance, and tribological performance similar to the Ni–P coating obtained using the common palladium activation. The Ni–P coatings obtained through cobalt and palladium layer activation from alkaline plating solution had a larger thickness than the Ni–P coating obtained from acidic plating solution. Therefore, the cobalt layer prepared on copper through galvanic replacement may serve as a viable alternative to palladium for activating electroless Ni–P plating. Graphical abstract

The effects of additives on the deposition rate, surface morphology, Ni and P elemental content of the electroless plating layer, and roughness of the electroless plating Ni-P layer were investigated. In an electroless plating Ni-P system, ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and sodium hypophosphite monohydrate were used as the complexing agent and reductant, respectively. The linear sweep voltammetry (LSV) polarization curve results showed that the compound addition of 1.0 mg L−1 L-tyrosine, 2.0 g L−1 saccharin, and 6.0 mg L−1 sodium dodecyl sulfate (SDS) could inhibit sodium hypophosphite oxidation and nickel ion reduction, which eventually reduced the Ni-P deposition rate. The Tafel polarization curves indicated that the compound additives obviously improved the corrosion resistance of the Ni-P electroless plating layer. Field emission scanning electron microscopy (SEM) images showed that the composite additives generated fine and uniform Ni-P electroless plating particles and enhanced the density, eliminated the surface cracks, and reduced the pinholes on the electroless plating layer surface. Atomic force microscopy (AFM) tests showed that the addition of complex additives improved the smoothness of the plated layer, the Ra value was reduced from 135.0 nm to 53.2 nm, and the Rq value was reduced from 164.0 nm to 93.0 nm. The final composition and implementation conditions of the EDTA-2Na-based Ni-P electroless plating system were determined. The deposition rate was 10.44 μm h−1, the P content of the electroless plating layer was 2.2%, and the electroless plating player was silver-white and bright.

Electroless Ni-P plating is an important process to enhance the corrosion and wear resistance of aluminum. However, due to the presence of an oxide layer on aluminum substrate, achieving a reliable Ni-P coating necessitates complex processes such as double zincate treatment or palladium immersion pretreatment. This study demonstrates that the copper immersion layer on an aluminum substrate can initiate the electroless Ni-P plating process. The copper immersion layer is deposited on the aluminum substrate through a convenient galvanic replacement reaction using an alkaline aqueous solution of copper sulfate and ammonia. This copper immersion layer can form a galvanic cell with the aluminum substrate, thereby initiating electroless Ni-P plating, similar to initiate electroless Ni-P plating by contact activation. It is confirmed that activation ability of the copper immersion layer is comparable to that of a palladium immersion layer by comparing the morphology, structure, deposition kinetics, and performance of Ni-P coatings obtained on copper and palladium immersion layers.

As internal combustion engines (ICEs) develop towards higher explosion pressures and lower weights, their structures need to be more compact; thus, the wall thickness of their cylinder liners is reducing. However, intense vibrations in the cylinder liner can lead to coolant cavitation and, in severe cases, penetration of the liner, posing a significant reliability issue for ICEs. Therefore, research on cylinder liner cavitation has attracted increasing interest. Gray cast iron is widely used in cylinder liners for its hardness and wear resistance; however, additional surface plating is necessary to improve cavitation resistance. This study developed a novel surface-modification technology using electroless Ni-P plating combined with high-temperature heat treatment to create cylinder liners with refined grains, low weight loss rate, and high hardness. The heat-treatment temperature ranged from 100 to 600 °C. An ultrasonic cavitation tester was used to simulate severe cavitation conditions, and we analyzed and compared Ni-P-plated and heat-treated Ni-P-plated surfaces. The findings showed that the combination of Ni-P plating with high-temperature heat treatment led to smoother, more refined surface grains and the formation of cellular granular structures. After heat treatment, the plating structure converted from amorphous to crystalline. From 100 to 600 °C, the weight loss of specimens was within the range of 0.162% to 0.573%, and the weight loss (80.2% lower than the plated surface) and weight loss rate at 600 °C were the smallest. Additionally, cavitation resistance improved by 80.1%. The microhardness of the heat-treated plated surface reached 895 HV at 600 °C, constituting a 306 HV (65.8%) increase compared with that of the unplated surface, and a 560 HV increase compared with that of the maximum hardness of the plated surface without heat treatment of 335 HV, with an enhancement rate of 62.6%.

As a method to mitigate fouling at the venturi flowmeter of pressurized water reactors, electroless nickel-phosphorus (Ni–P) plating and palladium (Pd) plating were conducted on AISI 304L stainless steel specimens and evaluated through a series of performance tests, including static corrosion testing, adhesion testing, and water loop testing using mock-up venturis. As expected from the zeta potentials, no iron oxide particles deposited on the surface of the plated specimens. The Ni-plated specimens exhibited localized corrosion, whereas the minimum oxidation was observed on the Pd-plated specimens. The water loop tests showed consistent results with the static corrosion testing. The adhesion forces after a four-month corrosion test were similar to those before. The overall performance tests indicated that electroless Pd plating on the inner surfaces of venturis could be a viable solution for mitigating fouling in pressurized water reactors.

A new strategy was applied to develop nano-quasicrystalline phase in well-known AlNiCo ternary system. This approach was based on electroless Ni-P plating of the starting powders and subsequent ball milling in a protective atmosphere without additional annealing or sintering processes. Microstructural evolution and phase transformation of both raw and coated particles were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. After 360 min of mechanical alloying, the peaks demonstrating the formation of nano-quasicrystalline phase appeared in XRD pattern of the coated powders, while those in mechanically alloyed raw powders remained mostly unchanged. The formation of nano-quasicrystalline phase in the vicinity of the primary elements was also confirmed by the corresponding selected area diffraction patterns, and images generated by transmission electron microscope (TEM).

To address the issue of poor corrosion resistance of the Mg–Li alloy, electroless Ni–P plating was used to create a protective coating. However, there were significant differences between the upper and lower surface coatings, which were summarized as follows: (1) compared with the lower surface, the longitudinal differences between different areas of the upper surface coating were larger; and (2) the denseness of the upper surface coating was insufficient in areas where the insoluble phase was concentrated, resulting in significantly lower corrosion resistance of the upper surface coating than the lower surface. Resolving these differences could compensate for the defects of the upper surface coating so as to improve the overall corrosion resistance of the material. Therefore, in this paper, the deposition process of Ni–P was observed and speculated, and the reasons for these differences were analyzed in combination with experimental phenomena. Based on these, two optimization measures were proposed. The SEM observation results showed that the differences between the upper and lower surface coatings were significantly reduced after optimization. The results of potentiodynamic polarization tests and EIS tests showed that the optimized upper surface coating had good corrosion resistance similar to the lower surface coating.

In this study, electroless-plating of a nickel-phosphor (Ni–P) thin film on surface-controlled thermoelectric elements was developed to significantly increase the bonding strength between Bi–Te materials and copper (Cu) electrodes in thermoelectric modules. Without electroless Ni–P plating, the effect of surface roughness on the bonding strength was negligible. Brittle SnTe intermetallic compounds were formed at the bonding interface of the thermoelectric elements and defects such as pores were generated at the bonding interface owing to poor wettability with the solder. However, defects were not present at the bonding interface of the specimen subjected to electroless Ni–P plating, and the electroless Ni–P plating layer acted as a diffusion barrier toward Sn and Te. The bonding strength was higher when the specimen was subjected to Ni–P plating compared with that without Ni–P plating, and it improved with increasing surface roughness. As electroless Ni–P plating improved the wettability with molten solder, the increase in bonding strength was attributed to the formation of a thicker solder reaction layer below the bonding interface owing to an increase in the bonding interface with the solder at higher surface roughness.

The electroless nickel-phosphorous (Ni-P) plating on polyester fiber using sodium hypophosphite as a reducing agent in alkaline medium was studied. The effects of plating parameters including concentrations, pH and bath temperature of the plating bath on deposition rate of the electroless Ni-P plating were investigated. The results reveal that the deposition rates increase with the increase in the concentration of nickel sulfate, sodium hypophosphite, pH and bath temperature, respectively. However, it is determined that the deposition rates decrease with the rise of sodium citrate. The kinetics of the deposition reaction was investigated and an empirical rate equation for electroless Ni-P plating on polyester fiber was developed.