WC-Co Hard Alloys Research Articles

Corrosion resistance of pressure/pressureless sintered cemented carbides with/without graphene oxide in NaOH solution

The electrochemical corrosion performance of WC-Co hard alloy was studied under pressure/pressureless sintering and conditions with/without graphene oxide added. Three electrochemical testing methods were used to evaluate the corrosion behavior: open circuit potential, electrochemical impedance spectroscopy, and dynamic potential polarization. The corrosion resistance of the alloy was compared using three parameters of corrosion potential, corrosion current density, and total impedance. The corrosion mechanism was studied by observing the surface morphology of corroded alloy using scanning electron microscopy and analyzing the surface corrosion products using X-ray photoelectron spectroscopy. The results showed that pseudo-passivation phenomenon appeared in the potentiodynamic polarization curve of the hard alloy in the sodium hydroxide solution. The corrosion behavior was mainly controlled by anodic dissolution, with the dissolution of WC phase being greater than that of Co phase. The corrosion resistant properties of the pressure sintered cemented carbide are higher than that of the pressure-less sintered cemented carbide respectively in NaOH solution, mainly because pressure increases the grain size and decreases the grain boundaries of cemented carbide, which can be regarded as the dislocation wall between grains and normally attacked by the serious corrosion preferentially.

Effect of the Tool Path on Hardness Uniformity in an Annular Zone of X20Cr13 Steel Surface-Hardened by Friction Stir Processing

This paper presents the numerical and experimental results of hardening of an annular zone on the flat surface of an X20Cr13 steel specimen by friction stir processing (FSP) with a WC-Co hard alloy tool moving along circular and fan-shaped paths. A finite element model of the process is proposed for predicting the temperature distribution through the width and depth of the annular zone for the considered tool paths and for detecting the reverse tempering regions. The influence of the paths of a cylindrical friction stir tool with a flat end on microhardness distribution in the surface layer of the hardened zone was studied experimentally. It was shown that FSP along the fan-shaped path provides uniform hardening of the annular zone, while processing along the circular trajectory leads to softening of the material in the regions where the friction tracks overlap. The uniformity of surface hardness in the friction stir processed annular zone of X20Cr13 steel was evaluated by calculating the “covering uniformity” (CU) index proposed by Campana. The hardening behavior is in full agreement with the results of finite element simulation of the FSP process. Hardness measurements and microstructural studies showed that the fan-shaped tool path provides surface layer hardening to a depth of 400 μm with the CU index ranging from 0.78 to 1.00. In the case of the circular path, the CU index ranges from 0.48 to 0.72 at the same depth. The proposed research methods can be applied to evaluate the FSP efficiency when using other workpiece and tool materials.

Effect of different precoating cleaning processes on the corrosion resistance of WC-Co hard alloy matrix

Effect of different precoating cleaning processes on the corrosion resistance of WC-Co hard alloy matrix

Enhanced Coarse-Grained WC-Co(Ce) Cemented Carbide Prepared through Co-Precipitation.

The exploration of coarse-grained WC cemented carbide has become a research hotspot for its application in the fields of rock cutting and mining; a key issue is how to achieve uniform dispersion and densification of the sintered phase, as well as how to obtain better mechanical properties. In this paper, chemical co-precipitation, combined with hydrogen reduction, was adopted. CoCl2·6H2O and CeCl3 were used as precursors to coat Co nanoparticles on the surface of WC powder while introducing different contents of cerium; the samples were then sintered and densified to obtain WC-Co(Ce) hard alloy materials. On the surface of the obtained WC particles, the distribution of Co(Ce) nanoparticles was uniform and dense, and the average particle size after sintering was 4.2 μm, which lies in the coarse-grained range. The addition of cerium elements significantly improves the flexural strength and impact toughness; when the cerium content was 0.5% and 0.6%, they increased to 2487 MPa and 36.1 kJ/m2, respectively. The addition of Co(Ce) through the co-precipitation method could achieve a uniform coating of the Co phase, along with the uniform dispersion and densification of the sintered phase, giving the WC-Co(Ce) cemented carbide excellent properties.

Structure and Frictional Properties of Ultrahard AlMgB14 Thin Coatings.

This paper presents the results of studies on AlMgB14-based ceramic coatings deposited on WC-Co hard alloy substrates using RF plasma sputtering. The aim of this work is to study the structure, phase composition, and mechanical properties of AlMgB14-based coatings depending on the sputtering mode. According to the results of the microstructural study, the bias voltage applied to the substrate during the sputtering process significantly contributed to the formation of the coating morphology. Based on the results of compositional and structural studies by energy dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy, it was found that the coatings are composed of nanocrystalline B12 icosahedrons distributed in an amorphous matrix consisting of Al, Mg, B, and O elements. The nanohardness of the coatings varied from 24 GPa to 37 GPa. The maximum value of the hardness together with the lowest coefficient of friction (COF) equal to 0.12 and wear resistance of 7.5 × 10-5 mm3/N·m were obtained for the coating sputtered at a bias voltage of 100 V. Compared with the COF of the original hard alloy substrate, which is equal to 0.31, it can be concluded that the AlMgB14-based coatings could reduce the COF of WC-based hard alloys by more than two times. The hardness and tribological properties of the coatings obtained in this study are in good agreement with the properties of AlMgB14-based materials obtained by other methods reported in the literature.

High temperature oxidation behavior of spark plasma sintered WC-CoCrFeNiAl hard alloys

The oxidation behavior of WC-CoCrFeNiAl hard alloy in air environment under 600–800 °C was studied and compared with that of WC-Co hard alloy. The results showed that the oxidation behavior of WC-CoCrFeNiAl hard alloy was controlled by the chemical reaction at the interface of matrix and oxide layer. The oxidation resistance of WC-CoCrFeNiAl hard alloy was significantly better than that of WC-Co hard alloy, and the high-temperature oxidation gain at 800 °C was only 60% of that of WC-Co hard alloy. The oxidation resistance of WC-CoCrFeNiAl hard alloy increases with the increase of high entropy alloy binder content, and the mass gain of WC-20CoCrFeNiAl hard alloy is only 14% of that of WC-5CoCrFeNiAl hard alloy. The excellent oxidation resistance of CoCrFeNiAl high entropy alloy improving the oxidation resistance of WC-CoCrFeNiAl hard alloys.

Interface characteristics and reinforcement mechanism of large-size WC-18Co reinforced Fe-matrix composites

WC-Co hard alloy has advantages of high hardness, high melting point and excellent wear resistance and thermal stability, its significant effect to the mechanical properties of metal matrix composites (MMCS). In order to obtain FMCS with excellent comprehensive properties, the influence of large-size WC-18Co particles on FMCS was studied. In this paper, WC-18Co/Fe composites were prepared by infiltration casting method. The phase composition, microstructure and interface characteristics of WC-18Co/Fe composites were studied. The residual stress, microhardness and wear resistance of WC-18Co/Fe composites were tested. The result shows that large-size WC-18Co particles have an effect of solid solution strengthening and dispersion strengthening. Nano-compounds and twins are produced in the transition layer, resulting in dislocation reinforcement of FMCS. The large-size WC-18Co particles generate residual compressive stress under the action of thermal stress. Elemental diffusion forms a special interface structure at the junction. The large-size WC-18Co particles improve the tribological properties of FMCS.

Synthesis of Quasi-two-dimensional Carbon Nanostructures in Atmospheric Plasma of the Arc Discharge Using WC-Co Hard Alloy Waste as a Catalyst

The results of experimental studies on carbon nanomaterials production in the plasma of an arc discharge initiated in an open air were presented. The possibility of using waste carbide tools as a catalyst for obtaining quasi-two-dimensional carbon nanostructures by the proposed non-vacuum electric arc method was revealed. It was concluded that the process of synthesis of carbon nanostructures and electric arc processing of waste based on tungsten and cobalt are compatible.

EFFECT OF THE TOOL PATH ON HARDNESS UNIFORMITY IN AN ANNULAR ZONE OF X20CR13 STEEL SURFACE-HARDENED BY FRICTION STIR PROCESSING

This paper presents the numerical and experimental results of hardening an annular zone on the flat surface of a X20Cr13 steel sample by friction stir processing (FSP) with a WC-Co hard alloy tool moving along circular and fan-shaped paths. A finite element model of the process is proposed for predicting the temperature distribution through the width and depth of the annular zone for the considered tool paths and for detecting the reverse tempering regions. The influence of the paths of a cylindrical friction stir tool with a flat end on microhardness distribution in the surface layer of the hardened zone was studied experimentally. It was shown that FSP along a fan-shaped path provides uniform hardening of the annular zone, while processing along a circular trajectory leads to softening of the material in the regions where the friction tracks overlap. The uniformity of surface hardness in the FSP-hardened annular zone of X20Cr13 steel was evaluated by calculating the CU index proposed by Campana. The hardening behavior is in full agreement with the results of finite element simulation of the FSP process. Hardness measurements and microstructural studies showed that the fan-shaped tool path provides surface layer hardening to a depth of up to 400 μm with a CU index ranging from 0.78 to 1.00. In the case of a circular path, the CU index ranges from 0.48 to 0.72 at the same depth. XRD analysis of the hardened layer revealed pronounced peaks corresponding to the (110)α, (200)α and (211)α lines, indicating the formation of martensite with different tetragonality at the given depth. The proposed research methods can be applied to evaluate the FSP efficiency when using other workpiece and tool materials.

Obtaining fine-grained hard alloys homogeneous in carbide grain

The actual task of this work is to obtain homogeneous hard alloys with fine carbide grains, combining high hardness and strength. Studies were carried out to establish the most favorable phase compositions of hard alloys and the most rational technical methodology for their production. In this research work, a nanostructured WC-TiC-Co powder charge was obtained by mechanochemical synthesis. Nanosized WC powder and nanopowder with precipitated Co were added to the hard alloy charge by mixing in a ball planetary mill. The process of pressing the powder charge at a pressure of 100-1000 MPa, as well as the sintering process at a temperature within the range of 1450-1600℃ was applied. The chemical-metallurgical method of deposition of metal layers from salt solutions was applied to obtain the WC-Co hard alloy. X-ray structural analysis and scanning electron microscopy were applied. The effect of the preparation method on the phase composition of WC-TiC-Co consolidated samples was studied. In the microstructure of these hard alloys, intercrystalline particles of (Ti,W)C are observed, and the presence of the liquid phase can lead to a rounded shape. It was found that the addition of nano-sized WC powder leads to an increase in pressed density. It was revealed that the addition of WC nanosize additives or WC nanopowder with deposited cobalt makes it possible to obtain a fine-grained structure with a grain size of not more than 4-6 microns. It was found that the addition of WC nanopowder with precipitated cobalt to the alloy has the highest Brinell hardness values; in addition, it leads to an increase in the bending strength.

Surface microstructure evolution mechanism of WC-Co hard alloy treated by high current pulsed electron beam

The surface of WC-Co hard alloy was modified treatment by high current pulsed electron beam (HCPEB). The surface microstructure evolution mechanism of WC-Co hard alloy was characterized by XRD, SEM, EBSD, and TEM, respectively. The temperature distribution of WC-Co hard alloy during HCPEB treatment process was calculated and discussed. The results show that rapid melting and rapid solidification induced by HCPEB caused the phase transformation and the microstructure evolution on the surface of the hard alloy, and when irradiation times was 13th times, the microcracks and voids on the WC-Co hard alloy surface were gradually healed by remelting repeatedly, causing the formation of dense nanostructures. The microhardness of the modified specimen surface layer by 13th irradiation increased to 1159.0 HV, and the wear resistance increased to 1.72 times that of the matrix. The strength and wear resistance of the surface layer of the specimen were improved due to the refinement of WC grains, the forming of WC1-X nanophase, and the precipitation of nanographite particles. The microstructure evolution mechanism on the alloy surface after the modified treatment was proposed that a metastable equilibrium system was formed (WC + WC1-X + Co3W9C4+graphite phase).

A Study of the Impact of Graphite on the Kinetics of SPS in Nano- and Submicron WC-10%Co Powder Compositions

This study investigates the impact of carbon on the kinetics of the spark plasma sintering (SPS) of nano- and submicron powders WC-10 wt.%Co. Carbon, in the form of graphite, was introduced into powders by mixing. The activation energy of solid-phase sintering was determined for the conditions of isothermal and continuous heating. It has been demonstrated that increasing the carbon content leads to a decrease in the fraction of η-phase particles and a shift of the shrinkage curve towards lower heating temperatures. It has been established that increasing the graphite content in nano- and submicron powders has no significant effect on the SPS activation energy for “mid-range” heating temperatures, QS(I). The value of QS(I) is close to the activation energy of grain-boundary diffusion in cobalt. It has been demonstrated that increasing the content of graphite leads to a significant decrease in the SPS activation energy, QS(II), for “higher-range” heating temperatures due to lower concentration of tungsten atoms in cobalt-based γ-phase. It has been established that the sintering kinetics of fine-grained WC-Co hard alloys is limited by the intensity of diffusion creep of cobalt (Coble creep).

Hard and wear-resistant niobium, molybdenum carbide layered coatings on WC-Co tools produced by ion bombardment and cathodic vacuum arc deposition

Phase and element composition, microhardness, adhesive strength, wear resistance and microstructure of the coatings and underlying layers formed on WC-Co hard alloy using Nb and Mo vacuum-arc sources were studied. It is shown that the influence of ion beams with energy of 1 keV created by Nb and Mo vacuum-arc sources for at least 1–2 min allows the formation of carbide coatings based on embedded metals and alloy elements with (Nb,W)C0.7, Mo2C and Co6W6C2 phases. The synthesis of carbide layers occurred by ion exposure by Nb or Mo at a surface temperature of the hard alloy of at least 1300 °C, controlled by an optical thermograph. Reducing of Nb and Mo ion exposure time down to 30 s does not allow heating of samples surface to temperatures above 700 °C, as a result, the formation of carbide layers on the alloy surface does not occur. The plasma deposition of NbC or MoC coatings on sublayers created by preliminary Nb or Mo ion treatment accompanied by heating of the sample surface up to 1300°С forms carbide layered system with hardness of 60 GPa, adhesive strength of 120–140 N and 2–3-fold lower volume wear compared to NbC and MoC plasma coatings deposited on a hard alloy without preliminary treatment.

Study of the kinetics of spark plasma sintering of ultrafine-grained hard alloys WC-10%Co

The effect of carbon on the kinetics of spark plasma sintering (SPS) of submicron powder compositions WC-10wt.%Co is investigated. Free carbon in the form of graphite was added into submicron powders by mixing. The activation energy of solid-phase sintering under the conditions of isothermal hold and continuous heating rate sintering was determined. It was shown that an increase in the carbon content leads to a decrease in the volume fraction of particles of the η-phase and a shift of the shrinkage curve to the region of lower heating temperatures. It was established that an increase in the graphite content does not significantly affect the activation energy of sintering of submicron powders in the region of “average” heating temperatures, the value of which is close to the activation energy of grain boundary diffusion in cobalt. It has been shown that an increase in graphite content leads to a significant decrease in the activation energy of compaction of WC-Co powders in the region of “high” sintering temperatures due to a decrease in the concentration of tungsten atoms in the γ phase based on cobalt. The kinetics of sintering of fine-grained WC-Co hard alloys is limited by the intensity of the cobalt diffusion creep by Coble.

Modeling of process of gear milling for definition of the intense deformed state in replaceable many-sided plates of a worm mill

The tool equipment plays an important role in work of machine-building enterprises. One of the most important elements of equipment is the metal-cutting tool [1]. Replacement of the tool from HSS of steel on the cutting tool with use of WC-Co [2-7] sintered hard alloys gives increase in productivity and overall effectiveness of processing [8-11]. When the cutting ability of material of the tool increases, the universality of its application decreases therefore the most rational is comprehensive research approach which considers design of the tool the used WC-Co hard alloy. Design, production and testing of the toothed cutting tools, working off of the modes of cutting have to be carried out concerning a specific work piece and its material. When developing this kind of the tool it is necessary to consider features of WC-Co alloy as the cutting material, the cutting modes, destruction of the tool and other moments connected with its use. Influence of an initial contour on distribution of tension in the replaceable cutting many-sided plate. Results of calculation of the intense deformed state in a replaceable plate from the material WC-Co. Zones of stretching and compression are observed on the main cutting edge. Concentration of the dangerous stretching tension is located in a transitional zone between the direct side cutting edge to top as in this zone there is the greatest constraint of cutting. Respectively, the greatest destruction will happen in this zone. Important, the fact that in this part of the cutting edge there will be the biggest wear on a back surface. The analysis of isolines of distribution of tension showed that the stretching tension along a front surface of the replaceable cutting plate decreases because each replaceable cutting plate cuts off the part of material. First, work is entered by the made narrower cutting plate which cuts off metal an upper part of the cutting plate, and then the underestimated cutting plate which works with the side cutting edges works. As a result of the conducted researches it was established that with the progressive scheme of cutting in comparison with the standard scheme of cutting at which the initial profile of the making rail is made on DIN3972 at gear milling, dangerous tensile stresses in the cutting hard-alloy plates significantly decrease.

The Feasibility of Usage TiN and CrN Barrier Sublayers for Improving the Adhesion of Polycrystalline Diamond Films on WC-Co Hard Alloys

In the present study, the influence of Chromium nitride (CrN) and Titanium nitride (TiN) sublayers on the adhesion of polycrystalline diamond films applied to WC-Co substrates was investigated. CrN and TiN layers were deposited on WC-Co substrates by magnetron sputtering in Ar/N2 atmosphere. Synthesis of diamond films was conducted in an AC abnormal glow discharge CVD reactor. The phase composition of the films was characterized by small-angle X-ray diffraction (XRD). The adhesion of diamond films was compared by analysis of Rockwell indentation imprints. It was found that TiN does not react with the carbon of the diamond film while CrN almost completely converted into chromium carbide (Cr3C2). Adhesion tests showed that the efficiency of these sublayers usage is substantially lower than using a Murakami and HNO3/H2O pretreatment.

Influence of production parameters of sintering on the structure and properties of VK5 hard alloy made of tungsten carbide SHS powder

The features of sintering of the WC-Co hard alloy of the VK5 brand using the feedstock of tungsten carbide powder fabricated by self-propagating high-temperature synthesis (SHS) are investigated. It is established that the physicochemical processes occurring when sintering hard alloys are similar to sintering processes of standard alloys made of traditional tungsten carbide powders. The hard alloy produced in this study possesses high hardness, strength, and crack resistance, which are characteristic of quasi-nanocrystalline materials.

The effect of structural state and temperature on mechanical properties and deformation mechanisms of WC-Co hard alloy

The publications reporting systematic investigations of the effect of structural state of WC-Co hard alloys (the cobalt binder content, WC grains size and contiguity) and temperature on mechanical properties and deformation mechanisms have been reviewed and generalized. The ductile-brittle transition, strain hardening, special features of WC-Co alloys deformations in various temperature ranges, and specificity of mechanical properties of the alloys with submicron WC grains have been discussed.

Effect of cobalt powder morphology on the properties of WC-Co hard alloys

The effect of cobalt powder morphology on the microstructure of WC-Co hard alloys produced by sintering cobalt + tungsten carbide powder mixtures has been studied using X-ray diffraction, laser diffraction, scanning electron microscopy, density measurements, and Vickers microhardness tests. The results indicate that, under identical sintering conditions, the densest and most homogeneous microstructure is formed in hard alloys sintered using cobalt powders consisting of rounded particles. The use of cobalt powders with dendritic morphologies impedes the homogenization of Co + WC powder mixtures and preparation of pore-free WC-Co hard alloys.

Dependence of the strength and plasticity of WC-6Co medium-grained hard alloys on deformation characteristics of the cobalt and carbide phases

The effect of deformation characteristics of the carbide phase and cobalt binder on the strength and plasticity of the WC-Co hard alloy has been studied using a calculation algorithm.