M. Rezrazi

Hardness, friction and wear characteristics of nickel-SiC electroless composite deposits

Abstract Composite coatings constitute a new class of materials which are mostly used for mechanical and tribological applications. Among these materials, nickel deposits with incorporation of hard ceramic particles such as silicon carbide (SiC), combine anti-corrosion properties (due to the presence of nickel), with mechanical and tribological performances (due to the presence of particles of SiC). In the present study, electroless Ni–SiC composite deposits with various amounts of SiC have been prepared and characterized. The first part of this paper considers the materials, the experimental conditions and the characterization of the coatings. The second part is dedicated to the study of the mechanical (hardness) and tribological (friction resistance and wear) properties of the co-deposits. Friction tests were carried out using a ball on disk tribometer. The mechanisms of wear were analysed from observations of the wear scars and their characterization using two-dimensional and three-dimensional profilometry. The results show that increasing the size or the rate of SiC particles incorporated lead to an increase in both the hardness of the films and friction coefficient when sliding against a steel ball.

Electrolytic and electroless coatings of Ni–PTFE composites: Study of some characteristics

Abstract This work consists of the realization and characterization of composite coatings of Ni–PTFE carried out by electroless deposition on the one hand and electrolytic deposition on the other hand, obtained by pulsed current (CPS) and d.c. current (DC). The evolution of some properties of these coatings generated by various procedures, properties such as morphology, hardness, ductility and wear resistance, are highlighted.

Some morphological characteristics of the incorporation of silicon carbide (SiC) particles into electroless nickel deposits

A size study of the particles in electroless nickel composite deposits was carried out in order to obtain information about the inclusion of silicon carbide (SiC) particles in the deposits. The surfaces and the metallographic cross-sections of the composite deposits were studied under a scanning electron microscope. The metallographic cross-sections of the composite deposits were analysed by observation under an optical microscope, coupled with the technique of image analysis and its data processing software. The results obtained indicated that the particles which are incorporated best are those which are well dispersed in the bath and whose size is smallest.

Determination of the incorporation rate of PTFE particles in Au-Co-PTFE composite coatings by InfraRed Reflection Absorption Spectroscopy

This work follows previous work dealing with the qualitative analysis of Au-Co-PTFE composite coatings for the determination of the PTFE amount in them. The analytical method of InfraRed Reflection Absorption Spectroscopy (IRRAS) which is performed at large angle of incidence (80°) was previously used, but not calibrated. The purpose of this paper is to realize this calibration so as to study the distribution of PTFE in the coating as a function of current density. The quantitative analysis of PTFE is made by EDS, thereby allowing the calibration of IR measurements. The importance of the surface preparation is pointed out especially for analyses by infrared spectroscopy.

Fast method of qualitative analysis of PTFE particles in the Au-Co-PTFE composite coatings by infrared spectroscopy

Abstract The purpose of this work is to characterise composite coatings of gold–PTFE formed by electrolysis. This characterisation requires the development of a fast and reliable method to determine the inclusion rate of PTFE particles in the coating. IR spectroscopy allows an easy qualitative analysis of the coatings. The fluoropolymer, which presents strong absorption bands can be characterised by this technique. EDS analysis and other methods are used to confirm the presence of PTFE and to validate the method. IR analysis is conducted by specular reflection (IRRAS). It allows, by successive polishings, to study the distribution of PTFE particles according to their depth in the composite coating. In a future paper, this qualitative investigation will be followed by a quantitative study based on the calibration of measurements in order to determine the incorporation rate.

Quantitative characterisation of Au–Co–PTFE composite coatings by differential enthalpic analysis

Abstract Energy dispersive spectrometry (EDS) and infrared reflection absorption spectroscopy (IRRAS) have been previously used for the qualitative and quantitative analysis of PTFE in gold–PTFE composite coatings. The inclusion rate of PTFE particles in the composite coating is determined close to the surface by these two methods and particularly within a thickness of 0.5 μm by EDS. Differential scanning calorimetry (DSC) is investigated for a direct determination of the inclusion rate of PTFE, independently of the depth in the coating. The gold matrix allows us to release from metal oxidation and, associated with PTFE (chemically inert), to isolate easily the composite coating by dissolution of the metal support. Correlation is made between the DSC and EDS methods previously proposed as detection tools.

Electrodeposition Behavior, Physicochemical Properties and Corrosion Resistance of Ni–Co Coating Modified by Gelatin Additive

The effect of gelatin on the microstructure, composition and electroplating mechanism of Ni–Co coating synthesized from sulfate media onto carbon steel substrate was investigated using AFM analysis, SEM/EDS and Electrochemical Quartz Crystal Microbalance (EQCM) coupled with chronopotentiometric measurements. The deposition of gelatin in the coating matrix was found to lower the mass of Ni–Co layers. Moreover, the adsorption of this additive seemed to inhibit the initial nucleation of the Ni–Co electrodeposition, showing homogeneous surface and smaller crystallites. Furthermore, the corrosion performance was studied in 3% NaCl solution by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). After a long immersion into chloride solution, Ni–Co–Gelatin (Ni–Co–Gel) coating showed a good stability and a better corrosion resistance. Therefore, the presence of gelatin additive impacted the crystal size, corrosion resistance and Ni–Co deposits morphology.