Effect of Electroless Coatings on the Mechanical Properties and Wear Behavior of Oriented Multiwall Carbon Nanotube-Reinforced Copper Matrix Composites

The effects of electroless coatings on the microstructure and composition of the interface between multi-walled carbon nanotubes (MWCNTs) and a Cu matrix and the mechanical properties and wear behavior of the resulting copper matrix composites were investigated. Ni and Cu coatings were electrolessly plated on MWCNTs and mixed subsequently with copper powder. Then copper matrix composites were prepared by sintering, hot extrusion and cold drawing processes. The results showed that MWCNTs were straight, long, uniformly dispersed and aligned in the composites. The Ni coating is more continuous, dense and complete than a Cu coating. The tensile strength, compressive strength, microhardness and tribological properties of Ni@MWCNTs/Cu composite along the drawing direction were enhanced most. The ultimate tensile strength and compressive strength were 381 MPa and 463 MPa, respectively. The friction coefficient and wear rate were reduced by 59% and 77%, respectively, compared with pure Cu samples. This study provides a new insight into the regulation of tribological properties of composites by their interface.

Preparation and characterization of electroless Ni coated nano alumina powder under different sensitization - activation conditions

The development of electroless coatings on various substrates has gained much interest among researchers for the sake of improved properties. However, the coating on ceramic particles as a source of reinforcement is still a challenge for the researchers and requires a good comprehension of fundamentals since the coating thickness relies upon many parameters. Particularly the sensitization and activation conditions are more important for the creation of an ideal environment to draw metallic ions as a coating layer. Therefore, this paper examines the role of sensitization and activation conditions on the viability of nickel coating on the alumina particles of an average size of 50 nm. A comparison is made between two environments, namely individual and blended activations in the preparation of coated particles. Characterization studies are also presented to support the discussion.

Comparison of corrosion resistance properties of Ni-P and Ni-W-P coatings obtained by electroless deposition

Corrosion resistance properties, such as porosity, stability in the atmosphere of NaCl mist, and anodic electrochemical activity in a sulfuric acid solution are studied and compared for Ni-W-P and Ni-P coatings obtained by electroless deposition. The studied coatings were obtained from solutions with glycine as the main ligand and contained 10.2 to 15.6 at.% of phosphorus and up to 3.3 at.% of tungsten. It is shown that Ni-W-P coatings with a tungsten content of 2.3 to 3.3 at.% and a thickness of 15 μm have a significantly lower porosity as compared with nickel-phosphorus coatings of the same thickness. Also, significantly better stability of Ni-W-P coatings in a NaCl mist atmosphere was observed, their corrosion damage degree is less than that of Ni-P coatings, and relatively little depends on the duration of exposure in a corrosive environment. Analysis of anodic polarization curves showed an almost similar electrochemical activity upon dissolution of Ni-P and Ni-W-P coatings in sulfuric acid. Both these types of electroless coatings showed a markedly better tendency to anodic dissolution than pure nickel. Taking into account the obtained experimental data, a conclusion is made as to the better protective characteristics of Ni-W-P coatings in comparison with nickel-phosphorus coatings. The main reason of the inferior protective properties of Ni-P coatings is their relatively high porosity.

Corrosion and Wear Behavior of Electroless Nickel Coatings

This chapter describes how corrosion is the degradation of a material due to a reaction with its environment. Wear is another deteriorating phenomenon which erodes the contacting surfaces of any mechanical component gradually. Although corrosion and wear are two different phenomenon they are often interdependent and in most practical situations take place simultaneously. Fortunately, several surface modification methods exist which can protect the surface of metal against corrosion and wear. Among them, electroless nickel coatings is a technology where a coating is applied without the use of external current source. The primary advantages of electroless coatings include uniform coating and ability to coat non-conductive materials. Electroless nickel coatings possess excellent properties such as high hardness, good wear resistance and corrosion resistance. The corrosion and wear behavior of these coatings mainly depend on bath ingredients, deposition conditions, heat treatment temperature, etc.

Effect of Heat Treatment on Tribological Properties of Ni-B Coatings on Low Carbon Steel: Wear Maps and Wear Mechanisms

Among the alternatives for using low-carbon steel in parts with heavy wear, as gears and bearing surfaces, Ni-B electroless coatings deposited on these steels are considered due to their wear resistance. Wear maps, elaborated from friction or wear results found for different evaluated conditions, are a very useful tool for the selection of materials based on tribological properties. However, wear maps for electroless Ni-B coatings are very scarce. In this work, dry sliding wear tests with different loads and sliding velocities were performed on Ni-B electroless coatings applied on AISI/SAE 1018 steel, with and without heat treatment at 450 °C for 1 h, with the aim of determining the effect of the heat treatment on the friction coefficients and wear rates. Contour and profile maps, and finally friction and wear maps, were constructed for each of the coatings evaluated. The coating properties before and after the heat treatment were studied by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), scratch tests, nanoindentation, and differential scanning calorimetry (DSC). Sliding wear tracks were studied using SEM, energy-dispersive spectroscopy (EDS), and micro-Raman spectroscopy. Good agreement between experimental and predicted values was found in friction and wear maps. Wear mechanisms change from flattening in less severe conditions to abrasion in more severe conditions, besides spalling and adhesive wear in untreated coatings. Moreover, abrasive wear is lower in heat-treated coating than in untreated coating.

EFFECT OF HEAT TREATMENT ON MICROSTRUCTURE AND CORROSION RESISTANCE OF Ni-B-W-Mo COATING DEPOSITED BY ELECTROLESS METHOD

The present work reports the deposition of a quaternary Ni-B-W-Mo coating on AISI 1040 medium carbon steel and its characterization. Quaternary deposits are obtained by suitably modifying existing electroless Ni-B bath. Composition of the as-deposited coating is analyzed by energy dispersive X-ray spectroscopy. The structural aspects of the as-deposited and coatings heat treated at 300[Formula: see text]C, 350[Formula: see text]C, 400[Formula: see text]C, 450[Formula: see text]C and 500[Formula: see text]C are determined using X-ray diffraction technique. Surface of the as-deposited and heat-treated coatings is examined using a scanning electron microscope. Very high W deposition could be observed when sodium molybdate is present in the borohydride-based bath along with sodium tungstate. The coatings in their as-deposited condition are amorphous while crystallization takes place on heat treatment. A nodulated surface morphology of the deposits is also observed. Vickers’ microhardness and crystallite size measurement reveal inclusion of W and Mo results in enhanced thermal stability of the coatings. Solid solution strengthening of the electroless coatings by W and Mo is also observed. The applicability of kinetic strength theory to the hardening of the coatings on heat treatment is also investigated. Corrosion resistance of Ni-B-W-Mo coatings and effect of heat treatment on the same are also determined by electrochemical techniques.