Ni SiC Composites Research Articles

Effect of magnetic field on electrocodeposition behavior of Ni–SiC composites

In this paper, an external magnetic field was applied in the electrodeposition of Ni–SiC composites, and its effects on surface morphology, SiC content, and crystal orientation were examined. It was found that the magnetic field modified the surface morphology and the orientation of the composites and significantly increased the SiC content. The phenomenon can be attributed to the change of charge transfer reactions and the mass transport process through the micromagnetohydrodynamic effect.

Equivalent circuit modelling of Ni–SiC electrodeposition under ramp-up and ramp-down waveforms

An equivalent circuit model (EC) for pulsed electrodeposition of Ni–SiC composite coatings was formulated and fit to electrochemical impedance spectra data for the system. Two different shaped waveforms, ramp-up and ramp-down waveforms both with relaxation time were applied to investigate the electrodeposition behaviour of Ni–SiC and to validate the equivalent circuit model. It was found that under the same average and peak current density, the shape of current waveform has significant effect on the electrodeposition behaviour. A higher instantaneous peak current for charge transfer was obtained by the ramp-up waveform, which results in finer grain size and enhanced hardness of the composites. The morphological characteristics of the Ni–SiC composites were also examined and the experimental results were in accordance with the predictions of the EC model.

Enhanced wear resistance of cast ductile iron by Ni-SiC composite coating

Unalloyed ductile iron (DI) has low resistance to wear. Its wear resistance can be enhanced by (i) hardening by heat treatment or (ii) deposition of a hard coating. The electrodeposition of Ni-SiC composite on unalloyed DI (GGG 40) has been investigated. The effect of operating conditions of the electrodeposition process using an acidic bath on the incorporation of SiC in the deposit was studied. Parameters studied included current density, inactivation and activation with PdCl2, and particle content. It was found that the volume per cent of SiC particles incorporated into the composite layer increased with increasing current density and with SiC concentration in the bath. The optimum SiC incorporation could be obtained using a bath with 60 g L−1 of SiC particles in suspension at 5 A dm−2, pH 4 and 50°C. The properties of the composite such as hardness and wear resistance were found to be significantly improved compared to the uncoated substrate. It appears economic to increase the wear resistance of as cast DI by application of the Ni-SiC composite by electrodeposition rather than using heat treatments or the addition of expensive alloying elements.

Analysis of tensile strength and microstructure of Ni–SiC composites prepared by electroforming

Ni–SiC metal matrix composites with two kinds of SiC content were prepared by electroforming in a nickel sulphamate bath. Tensile strength and microstructure of the composites before and after heat treatment were investigated. The maximum of tensile strength was obtained after heat treatment at 300 °C×24 h. The values were 641 N/mm2 and 701 N/mm2 respectively. The complete reaction between nickel and SiC particles can produce shrinkage pores in the interface. The volume of shrinkage pores was equal to 8% of the volume of SiC particles in the composites. The interfacial reaction products were composed of Ni3Si and a little amount of Ni31Si12 after heat treatment at 600 °C×24 h. The fracture evolution went though microcracks initiation, growth and coalescence. Cracking of the matrix, debonding of Ni–SiC interfaces and cracking of particles were three types of cracking modes for Ni–SiC composites.

Deposition behaviour and morphology of Ni–SiC electro-composites under triangular waveform

The deposition behaviour and morphology of Ni–SiC electro-composites were investigated under a triangular waveform. It was found that the grain size of the Ni–SiC composites decreased with increasing average current density, and the hardness of the composites increased with decreasing nickel matrix grain size. An equivalent circuit model based on the results of electrochemical impedance spectroscopy was formulated to simulate the charge transfer process under triangular waveform. Compared with deposits produced under the direct current, the triangular waveform with relaxation time provided a higher instantaneous peak current for charge transfer, which resulted in an improvement in morphology and hardness of the composites. The mathematical model was found to be in agreement with the experimental results.

The wear behaviour of electro-codeposited Ni–SiC composites

In this study, attempt has been made to investigate the wear resistance of Ni–SiC composites manufactured by electro-codeposition process, which is significantly correlated to the vol.% SiC in the matrix. In addition, the vol.% of SiC is closely related to the concentration of submicron SiC and the surfactant in the bath. It is found that the surfactant CTAB can not only disperse the SiC particles well in the electrolyte therefore leading to better homogeneously distributed SiC particles in the matrix but also enhances the SiC vol.% embedded in codeposition layer. It is confirmed that the wear resistance of codeposited layer increases with increasing submicron-size vol.% SiC.

Mechanical properties of nickel silicon carbide nanocomposites

Nanocomposite materials consisting of a nanocrystalline Ni matrix (grain size 10–15 nm) reinforced with sub-micron size SiC particulates (average particle size: 0.4 μm) up to 10.5 vol.% have been produced by pulse electrodeposition. Substantial improvements in mechanical properties including hardness, yield and tensile stress were obtained for the nanocomposite material, as compared with conventional Ni–SiC composites with a matrix grain size in the micrometer range. Tensile strengths up to four times that for conventional polycrystalline Ni and two times that for conventional polycrystalline Ni–SiC of comparable SiC content was measured. The tensile and yield strengths of the nanocomposite material with SiC content less than 2 vol.% were higher than those for pure nanocrystalline Ni of comparable grain size. For these nanocomposites an unexpected increase in tensile ductility was also observed when compared to pure nanocrystalline nickel. At higher SiC content (>2 vol.%) the strength and ductility were found to decrease to the detriment of the nanocomposite. Particle clustering was considered the main cause of this decrease.

Pulse electrodeposition of Ni–SiC nanocomposite

Nanocomposites consisting of a nanocrystalline Ni matrix (grain sizes 15–20 nm) reinforced with sub-micron size SiC particulates up to 3 wt.% have been produced by pulsed current electrodeposition. Microhardness values were about two times higher than those for comparable polycrystalline Ni–SiC composites, primarily due to the hard nanocrystalline Ni matrix.

The oxidation characteristics of electrodeposited nickel composites containing silicon carbide particles at high temperature

The oxidation behaviour of electrodeposited nickel and Ni-SiC composites containing up to 13% by volume of the carbide particles in flowing oxygen at 1100°C has been studied using various kinetic and electron-optical techniques. The electrodeposited nickel oxidized more slowly than cold-rolled nickel while the introduction of up to 13 vol.% coarse SiC particles (9 μm dia.) or up to 8 vol.% fine SiC particles (3 μm dia.) to the electrodeposited nickel did not significantly change its oxidation rate. The introduction of 12 vol.% fine SiC particles did cause a significant decrease in the oxidation rate due largely to internal oxide-derived particles acting as barriers to Ni 2+ ions diffusing through the NiO scale. The roles played in the oxidation process by doping, blocking effects in the oxide and internal oxide formation are considered and related to the oxidation rates of the composites.