Electroless nickel-phosphorus coating on Ti and Al elemental powders

Dual-layer (Cu and Ni coated W) coated powders were successfully prepared by electroless plating to fabricate high-density WCu composites with excellent mechanical properties. Field emission scanning electron microscope, transmission electron microscope and X-ray diffraction were used to analyze the microstructure and phase of sintered composites. Vickers hardness and bending strength of sintered composites were investigated. The results show that W powders were coated by Ni layer with a dense and uniform cell structure, the thickness of the Ni layer increased with the increasing of the content of Ni. Then Ni coated W composite powders were covered by Cu layer to prepare dual-layer composite coated powders (Cu and Ni coated W) with uniform and dense structure. WCu composites prepared from dual-layer composite coated powders with 2.48 wt% content of Ni can achieve high densification and strong mechanical strength due to the transformation of sintering mode and the formation of Ni₃P phase. Vickers hardness and bending strength can achieve to 257.9 HV and 953.80 MPa, respectively.

An electrochemically promoted electroless nickel–phosphorous plating process on titanium substrate is proposed. The influences of the temperature and current density on the phosphorous content, coating thickness and corrosion resistance are investigated. The results show that with the help of the electrochemical promotion, the uniform and amorphous nickel–phosphorous coatings with medium phosphorus content (6–8 wt%) are successfully prepared in the electroless bath at 40–60 °C. The phosphorous content of the coating increases with the temperature increasing, while decreases with current density increasing. Obvious passivation occurs for the nickel–phosphorous coatings during the anodic polarization in 3.5 wt% NaCl solution.

In this study, Ni coated aluminum nanoparticles were fabricated by electroless nickel deposition. Effect of two groups of parameters on the process plating rate were investigated: bath composition (main salt, reducing agent and complexing agent concentration) and process parameters (pH, plating time and bath temperature). Simulation of the process was performed using artificial neural network (ANN) media. Based on the presented model it is possible to design a high efficiency electroless bath, while minimum received materials are used and maximum plating rate is obtained. According to the model's results, 0.07 mol/l NiSO₄·2H₂O, 0.245 mol/l NaH₂PO₂·H₂O and 0.098 mol/l Na₃C₆H₅O₇·H₂O were chosen as the optimum electroless bath composition. The optimum bath parameters also were selected as pH of 9.5, temperature of 80 °C and 30 min of plating. At such condition, the most efficient Ni deposition, with maximum plating rate of 45%, was acquired on the surface of aluminum particles. These samples were characterized by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that a low phosphorus and nanocrystalline Ni layer, with about 30 nm thickness, has been coated on the aluminum nanoparticles.

In this paper nickel (Ni)-coated tungsten carbide (WC) composite powders have been synthesized by ultrasonic-assisted electroless plating with a simplified pretreatment at room temperature as the conventional sensitization and activation steps have not been employed. The growth mechanism of Ni layers and surface morphologies and composition of initial WC powders, pretreated WC powders and Ni-coated WC powders were analyzed by field emission scanning electron microscopy, and energy dispersion spectrometry. The results shows that uniform Ni-coated WC composite powders were successfully synthesized without conventional sensitization and activation steps by ultrasonic-assisted electroless plating at room temperature. The growth mechanism of Ni layers appears as follows: the surfaces of pretreated WC powders appear step-like defects which act as activated sites. Nucleation and the growth of nickel grains take place on the activated sites of pretreated WC powder, and the process repeats continuously on the lath particles with reticulate structure on the as-coated surfaces of previously deposited Ni-cells, finally Ni cells grow up and merge into a layer.

In this paper, infiltration behavior of W/Cu composite compacts made from coated tungsten powder has been investigated. For this purpose, tungsten particles were coated with Ni, Ni–P and Ni–Cu–P using electroless plating technique. Then the coated tungsten powders were compacted under selective pressures for control infiltrated copper in range 10–20 wt%. Infiltration process was carried out at 1300 °C under a reducing atmosphere. The effect of pre-coat of tungsten particles on microstructure, contiguity and density of infiltrated W/Cu compacts was evaluated by OM/SEM, EDS and Archimedes methods.

It was found that electroless plating of tungsten particles leads to more homogeneity microstructure so relative density of 99.3% was achieved for infiltrated compacts. The contiguity of W–W particles in the microstructure of composite made from Ni–Cu–P coated tungsten powder was lower than to other ones.

In the present research, tungsten particles were coated using nickel/nickel–phosphorus electroless plating technique. The coated tungsten powders were pressed under constant pressure to achieve compact material of cylindrical shape with same porosity. Then, attained compacts were infiltrated/penetrated by liquid copper under the hydrogen atmosphere in order to obtain W–15 wt.% Cu composites. The coated/uncoated powders as well as its infiltrated compacts were characterized by optical microscopy (OM) as well as scanning electron microscopy (SEM), EDS and XRD methods. The microstructure, relative density and specific resistivity of composites were compared. The microstructural observations revealed that the infiltration behavior can be improved in the compacts prepared by both nickel and nickel–phosphorus coated tungsten powders, in comparison with uncoated ones. In addition, it was found that relative density may be raised from < 85% to > 95% by nickel electroless plating, that leads to decrease specific resistivity from 6 to 4 µΩ cm. Enhancement of electrical conductivity of infiltrated W–15 wt.% Cu compacts prepared by electroless nickel coated tungsten powders was related to its higher density.