Carbide Composite Coatings Research Articles

Electrodeposition and characterization of chromium-tungsten carbide composite coatings from a trivalent chromium bath

The electrodeposition of chromium from a trivalent chromium bath has been described in this work. The electrocomposite coatings of chromium with hard abrasive particles were investigated. The chromium–tungsten carbide (CrWC) composite coatings were obtained by suspending different concentrations of WC particles in a trivalent chromium plating solution to improve the various properties of the chromium deposit layers. The effect of operating conditions on the deposit layers has been studied. On the other hand, the effect of non-ionic polymeric surfactant [nonyl phenol ethoxylate with 12 units of ethylene oxide (NPE)] as an additive in enhancing the incorporation of the WC ceramic particles in the chromium metal matrix was investigated. It was found that the co-deposition of the WC ceramic particles depends on the concentration of the additive and its efficiency in reducing the surface tension of the electroplating solution. The mechanism of incorporation of WC particles into a growing deposit was suggested and discussed in view of the zeta potential and degree of wetability of WC particles in the plating solution. Furthermore, the adsorption behaviour of the additive on WC particles was analysed according to the Frumkin isotherm. The surface morphology and the distribution of WC in the chromium metal matrix were investigated. The properties of the deposit layers, hardness, corrosion resistance and wear resistance were determined and compared with free chromium deposits. The test results reveal that the CrWC deposit layer shows better performance compared with the chromium-free deposit. Copyright © 2005 John Wiley & Sons, Ltd.

Influence of WC particle behavior on the wear resistance properties of Ni–WC composite coatings

Nickel-based and tungsten carbide (WC) composite coatings were prepared by laser cladding under different laser beam powers. The microscopic morphology and distribution of WC particles in a laser-clad Ni–WC coatings were characterized by scanning electron microscopy (SEM). Two effective methods to avoid the stress concentration and cracks were used. One is the gradient coating with WC hard phase varied gradually from the substrate to the top of the coating using three-step laser cladding. The other is the coating where WC particles, with a marked gradient distribution at interface between the matrix and WC, were uniformly incorporated in the coating by optimizing WC particle concentration, laser power and thickness of the layer. The wear test results show that three-step laser-clad gradient layer is not recommended especially for long-term wear applications because of the complicated laser processing and poorer interface between the matrix and WC particles.

The influence of current density and bath composition on the electrodeposition of nickel and nickel/silicon carbide composite

SUMMARYElectrodeposited nickel and nickel/silicon carbide composite coatings were obtained in a Watts-type bath. The influence of organic additives and current density on the microstructure and the grains size of the deposits was studied and the relationship between the nickel microstructure and the internal stress of deposits evaluated.

Microstructural characterization and wear behavior of laser cladded nickel-based and tungsten carbide composite coatings

Laser cladded nickel-based and tungsten carbide (WC) composite coatings were produced by varying laser beam power and were characterized by scanning electron microscopy. Microstructure of the clad layer is greatly affected by the processing parameters. The layer produced under the optimized processing conditions had uniform structure and excellent bonding with the substrate and was free of pores and cracks. Due to the right selection of the laser processing parameters, WC particulates partially dissolved, with the epitaxially grown dendrites around them, combined strongly with the coating materials and well-distributed in the layer. The larger the laser beam power is, the higher level of the dissolution of WC phase in metal matrix is, and the more WC particles tended to sink to the bottom of the layer. The wear test results show that the composite coating with WC hard phases has improved wear resistance when compared with the Ni-based alloy coating. The wear mechanism of the specimens is discussed based on microscopic observation of the worn surface and wear scraps.

Plasma spray deposition and high temperature characterization of ZrB 2–SiC protective coatings

Refractory metal borides are the object of special interest for aerospace applications requiring properties of chemical and mechanical resistance in ultra high temperature, such as nose and leading edges of re-entry space vehicles. The main objective of the research is the fabrication and characterization of plasma sprayed zirconium diboride–silicon carbide composite coatings and free-standing components for high temperature applications. High and low pressure plasma spray in a controlled atmosphere were selected as manufacturing techniques for the deposition of ceramic coatings. Fine ZrB 2 and SiC precursors were agglomerated and preconsolidated into spherical, hollow powders for better flowability and silicon carbide thermal protection during the interaction with the plasma. Coatings and free-standing tubular specimens were fabricated and tested for high temperature behaviour. Thermogravimetric analysis, surface morphology investigation and high temperature X-ray diffraction showed that the addition of approximately 25% SiC induces a mechanism of self-protection of the ceramic material during heat treatment in oxidizing environments up to approximately 2100 K.

Investigation of Structural and Mechanical Properties of Laser Deposited Microlaminate Hard Coatings

Nitride and carbide are superhard material with a high potential for applications in different fields. A new group of coatings are the multilayered/microlaminate coatings, which have shown very interesting properties. Single and microlaminate films were coated on Silicon (Si) substrates using pulsed laser deposition (PLD) technique. Films were deposited at different substrate temperatures in order to study the microstructure evolution and their effect on the mechanical properties of these microlaminate films. Structure of the films was characterized by x-ray diffraction (XRD) technique. Surface morphology and roughness of the films were investigated using atomic force microscopy (AFM). Hardness and modulus of the films were investigated using nanoindentation technique. It has been demonstrated that using boron carbide as a bottom layer increases the hardness and Young's modulus values of carbide composite coatings. Microlaminates of boron carbide/titanium carbides have shown higher hardness and modulus as compared to the microlaminates of nitride coatings.

Two-body abrasive wear of electroless nickel composite coatings

The two-body abrasive wear of electroless nickel (EN), EN-silicon carbide, and EN-alumina composite coatings have been investigated using a scratch test with a diamond indenter. The coatings were heat treated at temperatures of 100–500° C. The hardness of the coatings increased with heat treatment temperature from 500 HV100 for the as-deposited condition to 1008 HV100 when fully hardened. Scratch testing showed that the as-deposited coating had scratch tracks with a high degree of plasticity, signs of microploughing and tensile cracking and was characterised as a ductile failure. On the other hand, the heat-treated coatings showed chipping and cracking on the edge of the scratch tracks, failing in a brittle manner. The heat-treated EN-silicon carbide coatings, however, exhibited no cracking nor chipping, believed to be due to its higher fracture toughness than the other heat-treated coatings, attributable to its lower phosphorus content. The volume of material removed from the silicon carbide scratch track was 1/3 of the volume removed from the steel substrate at a 20 N load, and showed the best wear/ scratch resistance of any of the coatings tested.

The Effect of Carbide Content and Pre-Heat Treatment on the Oxidation Characteristics of Cobalt-Chromium Carbide Electrodeposits in Air at 1,000°C

The behaviour of cobalt-chromium carbide composite coatings at elevated temperatures has been shown to be influenced by the breakdown of the carbide particles. A series of deposits were produced wi...

ニッケル‐炭化けい素複合めっき技術の工業化

Attempts have been made to improve the thermal and wear resistance of electroplated nickelsilicon carbide composite coatings. Coating methods have been investigated by adopting an up-flow bath system, and the coated surfaces have been examined by using scanning electron microscopy. The amount of co-deposited silicon carbide was reduced by increasing the electrolyte flow rate. Films with 2.5-4.0 wt% co-deposit of silicon carbide were obtained at a current density of 30A/dm2, in the bath containing 200g/l of dispersed silicon carbide with 100cm/sec of flow rate. Addition of 0.2g/l of phosphorous, e.g. phosphorous acid, hypophosphorous acid, or sodium phosphite, to the electrolyte provided the film with greater thermal resistance. In the application of this composite film to a cylinder bore of 2-stroke engine, it turned out that wear loss of this coating was approximately 60 percent of that of conventional cast iron sleeve cylinder. After more than 20, 000km test running, the wear loss of the cylinder bore was less than 2.5μm in depth, around the top end position of the piston. Both the protruded silicon carbide powders on the nickel matrix surface produced by electrolyticpolishing and the hard nickel matrix obtained by adding phosphorous compounds have thus made the improvement of wear resistance possible.