Novel approaches on the study of wear performance of electroless Ni–P/diamond composite deposites

doi:10.1016/j.jmatprotec.2008.03.040

Journal of Materials Processing Technology

Volume 209, Issue 2, 19 January 2009, Pages 1004-1010

https://doi.org/10.1016/j.jmatprotec.2008.03.040 Get rights and content

Abstract

The ability to co-deposit particulate matter in a matrix of electroless nickel has led to a new generation of composite coatings. Polycrystalline diamond is one of the many varieties of particulate matter that can be co-deposited. Composite diamond coating is a regenerative layer of diamond particles dispersed in a hard electroless nickel matrix. In this work, experiments have been carried out to study the effect of heat treatment on the wear characteristics of the electroless composite coating containing diamond particles. The results indicate substantial increase in wear resistance after heat treatment. For wear analysis, in order to overcome the difficulties in the most common ‘weight loss’ method, X-ray diffraction method is used. Also the concept of internal standard method of quantitative X-ray diffraction analysis with suitable modifications is employed for the study of removal of diamond particles from the matrix. Superior integrity of the diamond particles with the matrix of the coating is observed for the specimens when heat treated to around 350 °C because of the formation of phosphides. But increasing the heat treatment to about 500 °C affects the wear resistance.

Introduction

Electroless composite coatings containing occluded solid particles in metallic matrices have been developed in recent years for various engineering applications those need good wear resistance in industries like textile, gear, paper, molding, tool and die, automotive, etc. Feldstein (1998) suggested that the enhancement in wear resistance can be achieved by co-depositing hard particles which possess high hardness and chemical inertness. There are various types of wear/erosion properties that could be improved by incorporation of particulate materials into the matrix. Wick (1986) established an implication from practice that hard coatings applied to cutting tool increases tool life by 2–10 times that of uncoated tools. Researchers like Abdel Hamid et al. (2007), Gay et al. (2007) and Sheela and Pushpavanam (2002) incorporated the abrasives such as oxides, diamonds and carbides, respectively, with Ni–P alloys and improved the micro-hardness and the wear resistance. Also Das et al. (2007) and Shrestha et al. (2004) found the suitable electroless composite deposits in wear applications. Charles and Shipky (1984) highlighted that among the hard particles, most interest appears to be in co-deposits involving diamond. The hardness values of co-deposits, estimated using conventional micro-hardness testers, provide only an average value for the hardness of the composite due to the dispersion of particles within the Ni–P matrix. Wang et al. (2003) reported that the hardness value estimated for diamond co-deposits is of the order of 10,000 VHN.

The first technology center for composite electroless plating was established in 1981. Christini (1997) has achieved successful co-deposition of artificial diamonds producing exceptionally wear-resistant coatings with excellent anchoring of the particulates within the matrix. Though diamond exists in various forms, polycrystalline diamond produced by shock synthesis method has been found to have several commercial applications. In the context of composite electroless coatings, several unique characteristics were reported when this form of diamond was employed in comparison to others. For example, Feldstein and Lancsek (1984) advocated that the exposed particles (polycrystalline diamond) have a catalytic tendency which makes the incorporated diamond particulates more adherent. Further, Fohl et al. (1989) and Grosjean et al. (2001) proved that the composite electroless nickel coatings possess enhanced mechanical properties when compared to similar conventional coatings.

The diamond and carbides have generally superior wear resistance, particularly when the deposit is heat treated to increase the hardness. Yongjun (1997) stated that the nature of the particles incorporated in composite coatings can significantly influence the wear resistance of deposits and/or lower the co-efficient of friction and impart lubricity. Even in this case, Feldstein et al. (1983) concluded that the wear resistance exhibited by deposits incorporating polycrystalline diamond is superior to that of composites having natural diamond as incorporated particulates. Reddy et al. (2000) studied the wear resistance of electroless Ni–P/diamond composite coatings from the view point of particle sizes. It is concluded that the coatings incorporating with finer diamond particles are more wear resistant when compared to those incorporating coarser ones. Zahavi and Hazan (1983) have shown better wear resistance for the coatings with smaller (3–6 μm) natural or synthetic diamond particles.

Hutchings (1998) proved the significant improvements in abrasion resistance of Ni–P coatings through suitable heat treatments. According to Duncan (1990), such improvements are attributed to the Ni₃P particle coarsening at higher heat treatment temperatures, and in view from Leon and Statia (1999), the changes in the microstructure occurred from the relatively ductile Ni–P to a duplex structure of hard Ni₃P in soft Ni matrix. Statia et al. (1997) concluded that there appears to be no direct relationship between the coating hardness and abrasive wear resistance; hardness cannot be considered as a key factor influencing the abrasive wear characteristics. Yating et al. (2006) reported that after heat treatment at 400 °C for 1 h, the wear rate of the hybrid composite decreased with an increase in micro-hardness.

Alirezaei et al. (2007) and Reddy et al. (2000) used a conventional method of calculating the wear resistances of the deposits from the weight reduction by employing pin-on-disc wear tests. Subramanian and Pallotta (1996) used a scratch test to analyze the wear behaviour of electroless nickel composite coatings and reported the plastic deformation of the as coated samples. But the information obtained regarding the wear characteristics of composite coating using weight loss method (i.e.) pin-on-disc and scratch method, is not complete in the sense that the weight loss does not discriminate between the loss of diamond particles and the loss of matrix material. Hence, this work explains the effect of heat treatment on the wear performance using X-ray diffraction method.

Section snippets

Production of composite coatings

In this work, mild steel discs of about 22 mm diameter and 7 mm thickness were prepared from rod stock to be used as substrates. All discs were then solutionised at 800 °C for 2 h and air-cooled to ensure uniform initial conditions.

The step-by-step cleaning procedure employed prior to plating consists of

1.
Cleaning the substrate with soap.
2.
Rinsing with distilled water.
3.
Ultrasonic cleaning in methanol.
4.
Acid pickling for 1 min [8% H₂SO₄ by volume].
5.
Rinsing in distilled water followed by a methanol wash.

Also

Incorporation of diamond particles

The ratio of the integrated intensity of the Bragg reflection from diamond particles in the matrix of the coatings to that from nickel could be considered as an indicator of the quantitative measure of diamond particles present in the matrix of electroless nickel (EN) coatings. Fig. 3 shows a typical XRD pattern from diamond in the range of interest in the present investigation. It is characterized by a single sharp peak around 56.3° (2θ) corresponding to the (1 1 1) reflection from diamond.

Conclusion

Based on the experimental results and analysis, the following conclusions have been drawn which clearly indicates the significant improvement of the wear performance on heat treatment.

•
Superior integrity of the diamond particles with the matrix of the coating is observed for the specimens when heat treated to around 350 °C because of the formation of phosphides.
•
Increasing the temperature of heat treatment to 500 °C, the wear resistance falls, due to the softening of the matrix material by grain

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Novel approaches on the study of wear performance of electroless Ni–P/diamond composite deposites

Abstract

Introduction

Section snippets

Production of composite coatings

Incorporation of diamond particles

Conclusion

Wear

Wear

Surf. Coat. Technol.

Tribol. Int.

Surf. Coat. Technol.

Wear

Met. Finish.

Wear

Electroless deposition and characterization of Ni–P–WC composite alloys

Surf. Coat. Technol.

Historical highlights of electroless plating

Plat. Surf. Finish.

X-ray Diffraction Techniques

Preparation and characterization of silicon nitride codeposited electroless nickel composite coatings

J. Alloys Compd.