The friction and wear of electroless Ni–P matrix with PTFE and/or SiC particles composite

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Abstract

In this paper, the friction behaviour and wear mechanism of electroless Ni–P matrix with PTFE and/or SiC particles composite coating are investigated by virtue of ring-on-disk wear machine at a high load of 150 N. The worn surface, wear debris and the composition changes after wear were characterized using scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). By comparison with Ni–P and Ni–P–SiC coatings, the results indicated that the combination of a PTFE-rich mechanical mixed layer (PRMML) formed on the worn surface and hard SiC were responsible for the good tribological properties of the hybrid Ni–P–PTFE–SiC composites at high load. After heat treatment at 400 °C for 1 h, the wear rate of Ni–P matrix composites decreased with corresponding increase in microhardness. During sliding, an obvious decrease in the temperature rise with PTFE addition was attributed to the good anti-friction of PTFE.

Introduction

Electroless nickel has been used as a versatile material to protect from wear and corrosion. Its wear resistance has been well-established by suitable heat treatment and as a composite coating by incorporation of hard particles, i.e. SiC, Al2O3, etc. or lubricating particles, i.e. PTFE, MoS2, graphite etc. into the Ni–P matrix [1], [2], [3], [4], [5]. Composite coatings, using electroless nickel as the matrix, have been applied in the surface finishing and engineering communities for many years.

However, the coating hardness of electroless Ni–P composites is correspondingly decreased with the volume fraction of lubricating particles in the coating, and the friction coefficient becomes worse because of the hard particles. It has been found that hybrid composites reinforced with high-strength ceramic particles and soft PTFE exhibit better tribological properties than mono-particle-reinforced ones, owing to the cooperative effect of the respective advantages [6]. Thus, it suggests a promising approach to producing Ni–P matrix hybrid composites with high wear resistance and low friction coefficient for wide applications. The investigations involved in hybrid composite coatings have been conducted by some specialists in recent years. Straffelini [7] studied the surface durability of double coating Ni–P–SiC/Ni–P–PTFE composites. Y.S. Huang et al. [8] discussed the microstructure and properties of Ni–P–PTFE–SiC. Additionally, Zhongcheng Guo [9] submitted the studies on the wear resistance and the structure of electrodeposited Re–Ni–P–W–SiC–PTFE. Deng et al. [10] submitted electrodeposited Re–Ni–W–SiC–PTFE composite and their properties. Few studies, however, were reported in the friction and wear behaviour of electroless Ni–P–PTFE–SiC composite, especially at high load.

This paper described the microhardness changes of Ni–P matrix composites after heat treatment at different temperature for 1 h. Comparing with Ni–P, Ni–P–PTFE and Ni–P–SiC, the friction and wear properties of Ni–P–PTFE–SiC were evaluated at high load. Emphases would have been put on the analyses of the anti-friction and wear mechanism.

Section snippets

Experiments

The coating with the thickness of 30 μm for each sample was deposited on 35×35×1 mm mild carbon steel by electroless nickel plating and the process parameters and conditions are shown in Table 1. The average size of SiC and PTFE are 3.5 and 0.2 μm, respectively. Perfluoro polyoxypropylene ammonium iodide (FC134) and hexadecyltrimethyl ammonium bromide (HTAB) surfactants were employed for particles dispersion and surface charge adjustment. Additionally, mechanical stirring was used to keep

Microhardness of the coatings

The microhardness of Ni–P and Ni–P composites as a function of heat treatment at different temperature were shown in Fig. 1. It was indicated that the microhardness of the four coatings significantly increased after heat treatment and reached the maximum at 400 °C. This was due to the formation of Ni3P alloy phase which generated the effect of precipitation hardening [11]. However, the microhardness of the four coatings had a little decrease after heat treatment at above 400 °C. This may be the

Conclusions

The dry friction and wear behaviour of Ni–P matrix composite with PTFE and/or SiC particles were investigated at high load. The wear resistance of the Ni–P matrix composites coincides well with the microhardness of each coating. Ni–P–PTFE exhibits the lowest friction coefficient and Ni–P–SiC has the lowest wear rate. At high testing load, Ni–P–PTFE–SiC presents the better anti-friction and wear resistance than other three Ni–P matrix composites. The PRMML formed on the worn surface is

Acknowledgements

The work is financially supported by Science and Technology Commission of Shanghai Municipality(No.035211037) and Science and Technology Commission Nano Special Fund of Shanghai Municipality (No.0352nm025).

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