Cobalt Matrix Research Articles

Friction performance of WC-Co coating with lithium grease and water lubrication

WC-Co coatings were sprayed by high-velocity oxygen fuel (HVOF) on bearing steels. The coating consisted of a high volume fraction of WC particles in cobalt matrix. The hardness of WC-Co coating was 60% higher than that of the bearing steel. The friction coefficients of WC-Co coating and bearing steel sliding against mild steel were tested with lithium grease and water lubrication. The friction results indicated that the friction coefficient increased with increasing loads. The friction coefficient of WC-Co coating was lower than that of bearing steels no matter with grease lubrication or with water lubrication.

Model System Studies of Wear Mechanisms of Hard Metal Tools when Cutting CFRP

Within the publicly-funded ZAFH research project SPANTEC light, the Competence Center for Tribology in Mannheim, Germany, examines the wear mechanisms of hard metal tools when cutting carbon-fiber-reinforced plastic in drilling and milling processes. The research project includes a test series with a tribological model test.The development of a new tribological simulation model system, a modified pin-on-disc system respectively called as edge-on-disc system, for cutting CFRP with hard metal composites is systematically analyzed and presented in this work. With this model system, a new method for tool wear analysis of the tool materials against CFRP is described.As result, there are further findings on the wear mechanism of the hard metal tungsten carbide in cobalt matrix (WC-Co) compared with carbon-fiber-reinforced plastic (CFRP). Research parameters for the tribological system in this paper are the WC-Co materials, with their WC-grain size and cobalt content, and the carbon fiber orientation.This study introduces a first approach to determine WC-Co wear compared with a CFRP-specimen, unlike most hard metal wear tests. Furthermore it is shown, that properties of the drilling and milling processes can be adapted by altering the model systems rotating speed and normal force. The results originality is also provided by using a variety of WC grain size classes (sub-μm to approximately 7-9μm grain size) and cobalt contents far above usual CFRP-machining properties to show the wear process between carbon fibers and WC-Co in detail.

Preparation and bioactive properties of chitosan and casein phosphopeptides composite coatings for orthopedic implants

Using the layer-by-layer deposition method, functional chitosan/casein phospopeptides (CS/CPP) composite coatings were produced on Co–Cr–Mo alloy. The CS/CPP composite coatings had the dendritic topography, and were quite hydrophilic. Zeta potential measurements showed the composite coatings were negative charged at neural pH. XPS results indicated that the CS/CPP composite coatings were covalently bond to the substrate. When MC3T3-E1 cells were seeded on the CS/CPP composite coatings, no cytotoxicity was observed. The bone morphogenetic protein-2 (BMP-2) mRNA expression was significantly up-regulated in MC3T3-E1 cells cultured on the composite coatings and it was twice as much as that of cells cultured on the bare substrate. The expression of osteoprotegerin (OPG) mRNA and the ratio of OPG/receptor activator of nuclear factor-κB ligand (RNAKL) mRNA were increased 5-fold and 55-fold, respectively. These results suggested the CS/CPP composite coatings may have potential application in cobalt matrix orthopaedic implants.

Modification of Electrodeposited Co-Pd Alloy Catalysts By Superimposed High Magnetic Field

Palladium and its alloys have been a subject of interest in many research centers all over the world. Due to the price and accessibility of Pd, intensive tests are conducted aiming to invent alloys with catalytic properties similar to those of platinum, but much cheaper than palladium itself. Alloys of Co-Pd, Pd-Fe, Pd-Ni and Pd-Cr exhibit high catalytic activity for the four electron oxygen reduction reaction.The properties of Co-Pd alloys for the hydrogen evolution reaction are close to the properties of pure platinum. This makes it possible to use them, for example, in fuel cells. Tests performed so far have demonstrated that the Pd-Co alloys are characterized by much better electrocatalytic properties for HER than pure palladium. Application of an external magnetic field during the deposition of an alloy causes an additional convection at the electrode surface through the magnetohydrodynamic effect (MHD), paramagnetic force and magnetic field gradient force. This additional convection results in changes of the alloy composition, structure and morphology, and these, in turn, affect the further properties as magnetic as catalytical of the produced alloys. Magnetic field applied parallel to the surface of the electrode generates convection (magnetohydrodynamic effect MHD) of the electrolyte; it results in a laminar flow on the surface of the electrode which reduces the diffusion layer and increases the concentrations gradients. This results in change of the size of the grains and thus can also influence the texture and formation of various phases of the deposits. These various effects can be caused at the same time by the above mentioned convection but also by the magnetic properties, when the field is superimposed the growth in the direction of easier magnetization appears. Optimal conditions of electrolytic deposition of cobalt matrix nanoalloys will be sought through selection of proper composition of electrolyte, changes of electrolysis parameters and by application of external electromagnetic field with intensity up to 12 Tesla. Initial experiments, when the magnetic field was limited up to 1 T, show the improvement of catalytical properties together with increase of magnetic field orientated parallel to the surface of electrode. The influence of magnetic field with higher strength on electrodeposition of alloys with catalytical properties is needed to be clarified. Acknowledgement This work was supported by Polish National Science Center under grants 011/01/N/ST5/05509 and 2013/09/B/ST8/00211. This work was also supported by Polish Ministry of Science and Higher Education under grant IP2012/001072.

Grinding of sub-micron-grade carbide: Contact and wear mechanisms, loading, conditioning, scrubbing and resin-bond degradation

An investigation was made into grinding of sub-micron-grade tungsten-carbide in a cobalt matrix. Grit-workpiece contact and loading mechanisms were analyzed. Loading-removal methods – via conditioning and a cleaning nozzle – were analyzed both in terms of fundamental mechanisms and removal efficacy. A novel method of quantifying wheel-conditioning parameters was developed and validated experimentally. Wheel-wear mechanisms were investigated in terms of thermally-induced grain pull-out, particularly under low-aggressiveness conditions. A fundamental difference in the size-effect was seen for sub-micron grades.

Impact and Penetration of SiC: The Role of Rod Strength in the Transition from Dwell to Penetration

The phenomenon of dwell during projectile impact on ceramics has been an active area of research for several decades. Dwell in confined ceramics has received much attention, particularly the role of cover plates and their influence over the dwell to penetration transition. Dwell during long rod impact on unconfined ceramics has received relatively less attention. The present work will compare and contrast the results of two series of long rod impacts on hot pressed silicon carbide targets. One series utilized gold wire rods. The other series utilized rods fabricated from tungsten carbide with 10% cobalt matrix. A novel ten-flash X-ray system captured spatially resolved images of the penetration events. The experimental results are compared with simulations and predictions from the Alekseevskii-Tate equation to explore the role of shock pressure, the effects of the strength of the rod material in dwell to penetration transition behavior, and the behavior of defects within silicon carbide.

Deposition of protective coatings by electric arc cladding with SHS electrodes

Coatings were produced by electric arc cladding with self-propagating high-temperature synthesis, based on a titanium carbonitride hard alloy and a cobalt binder. The results show that the deposited layer consists of three characteristic zones containing titanium carbide grades, distributed in the iron–cobalt matrix. The content of the titanium carbide grains in the coating reached 80%. The hardness of the deposited layer was 56–58 HRC. Industrial tests of the deposited areas of a jaw breaker in the zone of the effect of maximum loading showed that the rate of wear of the deposited layer is 1.5–2 times lower than the rate of wear of the lining made of 40Cr steel.

Structural-Phase States and Mechanical Properties of VK8 Alloy after Gamma-Quanta Irradiation

. This article on the basis of experimental studies shows the data about γ-quanta affecting VK8 alloy. With structural studies it is found that γ-quanta irradiation leads to the volume fraction of the ternary phase and a decrease in the concentration of defects in cobalt. The irradiation γ-quanta irradiation leads to an increase in the content of the ternary compound type η-phase (CoxWyC) of variable composition and decrease the concentration of defects in the cobalt matrix. Formation of the ternary compound by irradiation determines the mechanical properties of the alloy, because the appearance η-phase results in an alloy with a grain size of less hardness alloys.

Studies on the Codeposition of SiC Nanopowder with Nickel, Cobalt, and Co-Ni Alloys

Electrodeposition of SiC nanopowder (approximately 120 nm) with nickel, cobalt, and Co-Ni alloy matrix was studied. It was found that particles suspended in the bath affect slightly the reduction of metallic ions. Incorporation of the ceramic particles was governed mainly by the morphology of the matrix surface, while no strict correlation between the amount of cobalt ions adsorbed on the powder and the SiC content in the composites was found. Microhardness of nickel deposits was 585±5 HV, while for cobalt-rich coatings (84–95 wt.% Co) the values were in the range of 260–290 HV, independently of the SiC content in the coatings. Fine-grained nickel deposits were characterized by good corrosion resistance, while cobalt and Co-Ni alloys showed high corrosion current densities.

Numerical Modelling of Stress/Strain Field Arising in Diamond-Impregnated Cobalt

Abstract The paper presents results of computer simulations of the stress/strain field built up in a cobalt matrix diamond impregnated saw blade segment during its fabrication and after loading the protruding diamond with an external force. The main objective of this work was to create better understanding of the factors affecting retention of diamond particles in a metallic matrix of saw blade segments, which are produced by means of the powder metallurgy technology. The effective use of diamond impregnated tools strongly depends on mechanical and tribological properties of the matrix, which has to hold the diamond grits firmly. The diamond retention capability of the matrix is affected in a complex manner by chemical or mechanical interactions between the diamond crystal and the matrix during the segment manufacture. Due to the difference between the thermal expansion coefficients of the diamond and metallic matrix, a complex stress/strain field is generated in the matrix surrounding each diamond crystal. It is assumed that the matrix potential for diamond retention can be associated with the amount of the elastic and plastic deformation energy and the size of the deformation zone occurring in the matrix around diamonds. The stress and strain fields generated in the matrix were calculated using the Abaqus software. It was found that the stress and strain fields generated during segment fabrication change to a large extent as the diamond crystal emerges from the cobalt matrix to reach its working height of protrusion.

Surface Quality of Amilled Gamma Titaniumaluminide for Aeronautical Applications

Abstract Gamma titanium aluminides are an interesting alternative for nickel, iron or cobalt matrix superalloys. Due to the advantageous strength properties at high temperatures they can successfully replace superalloys in applications such as high pressure compressor blades, low pressure turbine blades, high pressure compressor case, low pressure turbine case. Milling is one of the processes that can be applied in the forming elements made from this type of alloys for the aviation industry. Research included the selection of tool, the process kinematics and the range of milling gamma titanium aluminide (Ti-45Al-5Nb-0.2B-0.2C) process parameters were carried out. Milling can be an effective method of forming of elements made of gamma TiAL in the range of processing parameters: vc = 20-70 m/min, ap = 0.3-0.7 mm, fz = 0.1- 0.45 mm/tooth. In the tests carried out the best results were obtained using a R300-016A20L- 08L milling cutter, S30T tool coating and in-cut milling.

Comparative Studies on the Corrosion and Scratchbehaviors of Plasma Sprayed ZrO2 and WC-Co Coatings.

This paper deals with the fabrication of WC-12wt%Co and Yttria-stabilized Zirconia coatings fabricated using Atmospheric Plasma Spraying technique.The Microstructural Characterization of the coatings was carried out using Scanning electron microscope(SEM).Potentiostat was employed to perform corrosion testing for the bare substrate and the coatings in 5wt %Nacl solution. The adhesion between the coating and the substrate was assessed using Scratch testing machine. The results suggested that WC-12wt%Co coating offered enhanced Corrosion and Scratch resistance when compared to that of the Yttria stabilized Zirconia coatings. This enhancement could be mainly ascribed to the presence of few amounts of interconnected pores and hard tungsten carbide particles embedded in the cobalt matrix.

Preliminary Characteristic of Composite Coatings C/Hap Produced Respectively by Rf Pacvd and Sol–Gel Methods

The required high mechanical strength and the reliability of implants on one side and a lack of toxic elements in those materials, on the other side, causes restrictions in use of metal alloys for austenitic steel, alloys of cobalt matrix and even titanium alloys. However, elements harmful to human body structure such as chromium, nickel and vanadium could not have been eliminated so far. An attempt to reduce detrimental effects of above elements on the living organism are surface modifications of materials predicted for implants through the deposition of protective layers. The C/HAp composite coating was prerared by deposition of carbon layer directly on surgical steel with RF PACVD method and manufacturing of hydroxyapatite layer by sol-gel method. It was proved that carbon film significantly increases adhesion of the composite C/HAp coating. It is due to the diffusive character of bonding between carbon layer and metallic substrate not only by adhesion as in the case with hydroxyapatite deposited directly on metal base. Adhesion of both synthesized coatings was determined using nanoindentation technique. X-Ray diffraction was used for phase composition evaluation. Atomic Force Microscope revealed topography of raw, carbon and C/HAp surfaces. Elemental composition of carbon and composite layers was investigated by scanning electron microscope equipped with x-ray energy dispersive spectroscopy detector.

Abrasive Wear Mechanism in Near-Nano and Microstructured WC-Cobalt Coatings

Abrasive wear mechanism in HVOF sprayed near-nano and microstructured WC-17wt.%Co coatings was studied. The crack propagation mechanism shows that it propagates only through cobalt matrix in the case of near-nanostructured coatings while both trans-granular and intergranular crack propagation was observed in the microstructured coatings. SEM images show a relatively ductile failure mechanism in the near-nanostructured coating, while a brittle failure mechanism dominated in the microstructured coating. AFM images show that the worn surface is smooth in near-nanostructured coatings with an average roughness value of 19 nm, while the roughness on the microstructured coating worn surface was recorded at 83 nm. Further, the wear debris formed on the near-nanostructured coated surface was mostly spherical and finer, whereas this was irregular and coarser in the microstructured counterpart. The wear behaviour suggested a lower wear rate in the near-nanostructured coatings than the microstructured coating. This was further confirmed by abrasive wear tests results.

Electrochemical Impedance Spectroscopy and Corrosion Behavior of Co/CeO2 Nanocomposite Coatings in Simulating Body Fluid Solution

A series of Co/CeO2 (25 nm) nanocomposite coating materials by electrodeposition were successfully prepared containing different cerium oxide composition in the cobalt-plating bath. Stainless steel (304L) was used as support material for nanocomposite coatings. The nano-CeO2 is uniformly incorporated into cobalt matrix, and the effect on surface morphologies was identified by scanning electron microscopy with energy-dispersive X-ray analysis. Codeposition of nano-CeO2 particles with cobalt disturbs the regular surface morphology of the cobalt coatings. It should be noted that the as-prepared Co/CeO2 nanocomposite coatings were found to be much superior in corrosion resistance over those of pure cobalt coatings materials based on a series of electrochemical impedance spectroscopy measurements in simulating body fluid solution. With increase in the nano-CeO2 particles concentration in the cobalt electrolyte, it is observed that the corrosion resistance of Co/CeO2 increases. Co/CeO2 nanocomposite coatings have higher polarization resistance as compared with pure cobalt layers in simulating body fluid solution.

Electrosynthesis and performances of cobalt–ceria nanocomposite biocoatings

Co–CeO2 nanocomposite coatings were obtained by electrocodeposition of nanoparticulate cerium oxide bioceramic (25 nm mean diameter) into cobalt matrix on stainless steel support and the resulting properties were evaluated comparatively with pure cobalt layers. The surface and anticorrosion properties in the simulating body fluid (SBF) solution of the obtained Co–CeO2 nanocomposite layers are characterised using scanning electron microscopy with energy dispersive spectroscopy system, ultrahigh microtopography, Vickers surface microhardness, linear polarisation and electrochemical impedance spectroscopy techniques. The results indicate that CeO2 nanoparticles are uniformly dispersed into cobalt matrix and influence the surface morphology, microtopography, and microhardness and corrosion behaviour of nanocomposite coatings obtained. Coating thickness increases with increased current density as well as the surface roughness and microhardness. At the same time, the results obtained by corrosion tests show that when compared with the traditional polycrystalline cobalt films, the obtained Co–CeO2 nanocomposite layers exhibit the enhanced corrosion resistance in the SBF solution.

Transport and magnetic properties of PrCo1−xNixO3 (x = 0.0–0.7)

The influence of Ni substitution on the transport and magnetic properties of the perovskite PrCo1−xNixO3 (x = 0.0–0.7) has been investigated by synthesizing and characterizing different samples. The unit cell volume of orthorhombic crystal structure expands with increasing Ni content, affecting the distortion of M–O (I, II)-M bond angles (M = Co, Ni). The expansion of the unit cell volume can be attributed to the larger ionic radii of Ni2+ and to the stabilization of the intermediate-spin state in the low-spin cobalt matrix. The electrical conduction mechanism varies with the Ni content with noticeable change from variable range hopping to nearest neighbour hopping in compositions 0.07 ⩽ x ⩽ 0.29. The Seebeck coefficient is positive for samples with 0.0 < x < 0.49. Only PrCo0.3Ni0.7O3 has a negative Seebeck coefficient. The ZFC/FC curves and M (H) hysteresis loops reveal both a spin-glass behaviour and ferromagnetic ordering below the Curie temperature (TC) for Ni-substituted samples. By the combination of Seebeck coefficient data and the measured effective magnetic moment μeff, the mixed valences of Co3+/Co4+ and Ni2+/Ni3+ in PrCo1−xNixO3 compounds were determined and the values are in agreement with x-ray photoemission spectroscopy measurements.

Co-ZrO 2 electrodeposited composite coatings exhibiting improved micro hardness and corrosion behavior in simulating body fluid solution

The aim of this work was the deposition of zirconium oxide bioceramic particles in cobalt matrix within the research work aimed at obtaining metal matrix composite coatings (MMC) under direct current and the evaluation of their protective properties. The cobalt/zirconia micro structured composite coating containing bioceramic of ZrO 2 dispersed phase was prepared using direct current (DC) electrodeposition method. The surface morphology, cross section and anti-corrosion property in SBF solution of the obtained Co/ZrO 2 composite films, are characterized using optical microscopy, scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS) system, atomic force microscopy (AFM), ultrahigh-micro-topography, linear polarization and electrochemical impedance spectroscopy (EIS) techniques. The results indicate that, ZrO 2 particles are uniformly dispersed into Co matrix and influence the surface microtopography, microhardness and corrosion behavior of composite coatings obtained. Coating thickness increases with increased current density as well as the surface roughness and microhardness. At the same time, the results obtained by polarization curves and EIS methods show that, when compared with the traditional polycrystalline Co film, the obtained Co/ZrO 2 composite film exhibits the enhanced corrosion resistance in SBF solution.

Co-electrodeposition of inorganic fullerene (IF-WS 2) nano-particles with cobalt from a gluconate bath with anionic and cationic surfactants

The codeposition of IF-WS 2 particles (130 nm diameter) in a cobalt matrix has been investigated. The influence of cobalt content and anionic and cationic surfactants on composite coatings produced using direct current (DC) and pulse reverse plating (PRP) are described. The coatings were assessed by XRD, SEM and EDX. The cationic surfactant promoted particle encapsulation and high oxygen content in DC coatings, whilst anionic surfactants do not offer controlled particle codeposition. Improved particle content and distributions were obtained by PRP, on the high cobalt bath containing anionic surfactant. The particle content was optimised by fixing the anodic cycle time t a, and varying the cathodic cycle time, t c. Sound coatings with a high percentage (11 vol.%) of particles were produced at t c of 60 s. This was encouraged by electrophoretic attraction of particles in the anodic phase and then encapsulation during the cathodic phase of the cycle.

Influence of CTAB cationic surfactant on codeposition of SiC particles with cobalt

Electrodeposition of SiC particles in a cobalt matrix in the presence of cetyltrimethylammonium bromide (CTAB) as a cationic surfactant has been carried out. The inhibiting effect of CTAB (0–1·1 mM) on the cathodic process was observed during the establishment of polarisation curves in galvanostatic and potentiodynamic measurements. The surfactant enhanced SiC incorporation into the matrix from ∼5 vol.‐% in the absence of CTAB to ∼30 vol.‐% at 1·1 mM CTAB for two current densities (0·5 and 1·0 A dm−2). The presence of cationic surfactant in the bath decreased the adsorption of Co2+ ions on SiC, but increased Br− adsorption was simultaneously observed. Current efficiencies were correlated with Co2+/Br− molar ratios for the ions adsorbed on the particles. The structure of the composite coatings was studied microscopically. Microhardness of the deposits (200–500 HV) was also determined.