Alloy Binder Research Articles

Fracture behavior of cemented carbides with CoNiFe medium entropy alloy binder

In this study, we prepared WC-CoNiFe and WC-Co with different grain sizes by sintering-hot isostatic pressing (SHIP) and evaluated their fracture behavior. The results showed that WC-CoNiFe has a higher fracture toughness (between 13.16 and 17.82 MPam1/2) than WC-Co (between12.08 and 16.21MPam1/2). Moreover, fracture toughness and fatigue crack growth (FCG) were closely related to the corresponding microstructural characteristics. The fracture toughness increased via ductile ligament bridging and crack deflection as the mean free path of the binder phase (λCo) increased, or the contiguity of the carbide phase (CWC) decreased. The fatigue fracture mode showed a transition from a cleavage-like brittle fracture to a ductile dimple-like fracture. The fatigue sensitivity of cemented carbides was positively related to the fracture toughness. As the fracture toughness increased, cemented carbides exhibited a transition from ceramic-like material to metal-like material. Considering two important controlling parameters of FCG behavior, the effect of maximum stress intensity factor (Kmax) on FCG was dominant compared to the stress intensity factor range (∆K). However, the difference in the relative influence of these two parameters diminished as the fracture toughness increased. Moreover, with the rise in Kmax value, we defined three stages of the FCG process: crack initiation, stable crack growth, and unstable crack growth. The results suggest that CoNiFe medium entropy alloy is a promising material for application as a binder phase of cemented carbides with high toughness.

Oxidation behavior of ultrafine WC-based cemented carbides with AlxCoCrCuFeNi high-entropy alloy binders

The isothermal oxidation behavior of WC-based cemented carbides with AlxCoCrCuFeNi (x = 0, 0.5, 1.0, 1.5) high-entropy alloy (HEA) binders at 600–800 °C in air was studied by a thermogravimetric method, as well as WC-Co for comparison. The oxidation of the WC-HEA cemented carbides accompanies swelling and follows a linear law that is controlled by reaction at the oxide layer/matrix interface. The WC-HEA cemented carbides show better oxidation resistance than WC-Co, even though WC-Co has a denser microstructure and coarser WC grain size. With increase of Al content in the HEA binder, the oxidation rate of WC-HEA decreases, and the specific mass gains of the samples with HEA binder containing Al are at least 20% smaller than that of WC-Co after isothermal oxidation at 800 °C for 2 h. Moreover, as the HEA content increases from 5 to 20 wt%, the specific mass gain reduces from 61.89 to 24.55 mg/cm2. Selective oxidation of the HEA binder occurs, and the excellent anti-oxidation property of the HEA binder impedes inward diffusion of oxygen to the oxide layer/matrix interface, which suppresses oxidation of the matrix and enhances oxidation resistance of the WC-HEA. The results also indicate that the improved oxidation resistance of the WC-HEA system should not be attributed mainly to the formation of a dense oxide layer with high tungstate content during oxidation.

Microstructure and mechanical properties of WC or Mo2C modified NbC-Ni cermets

In this study, the influence of up to 15 vol% WC or Mo2C addition to Ni bonded NbC matrix cermets, prepared by pressureless liquid phase sintering in vacuum for 90 min at 1390 °C was assessed. The constituent phases and W/Mo dissolution in the Ni binder and NbC phases were simulated by thermodynamic modelling. Microstructure and phase analysis using XRD and SEM indicated that the WC or Mo2C modified NbC based cermets were composed of a (Nb,W)C or (Nb,Mo)C solid solution cubic phase dispersed in a cubic Ni alloy binder. Residual WC was present in the cermets with ≥10 vol% WC addition, whereas up to 15 vol% Mo2C addition completely dissolved into the NbC cermets. The phase evolution and influence of the WC/Mo2C content on the solid solution formation is discussed and the fracture toughness, Vickers hardness and transverse rupture strength was assessed.

Microstructure and mechanical properties of WC and Ti(C0.7N0.3) modified NbC solid solution cermets

Eight NbC solution matrix cermets were prepared by liquid phase sintering of mixtures containing NbC, WC, Ti(C0.7N0.3), Mo2C, Co and Ni powders. The influence of the WC and Ti(C0.7N0.3) content on the microstructure and mechanical properties of the cermets was investigated. Microstructural investigation was supported by thermodynamic equilibrium calculations to predict the composition of the constituent phases as a function of WC content at 1420 °C. The results indicated the variation in WC and Ti(C0.7N0.3) content had a significant influence on the phase content, the in-situ formed (Nb,W,Ti,Mo) (C,N) solution grain growth and concomitant mechanical properties. The NbC solution cermets with 12–32 wt% WC were composed of a core-rim (Nb,W,Ti,Mo) (C,N) phase, Co–Ni alloy binder, and rimless Ti(C0.57N0.43) phase. XRD phase analysis and simulations revealed that the composition of the cubic structure (Nb,W,Ti,Mo) (C,N) and Ti(C,N) solid solutions depend on the WC content. The NbC matrix cermets with 12–32 wt% WC exhibited a Vickers hardness (HV30) of ∼1500 kg/mm2 and indentation toughness of ∼9 MPa m1/2.

Effect of titanium binder addition on the interface structure and three-body abrasive wear behavior of ZTA ceramic particles-reinforced high chromium cast iron

The effects of Ti alloy binder addition on the wettability, interface microstructure, and three-body wear behaviors of ZTA ceramic particle-reinforced composites were investigated systematically. With binder addition from 5% to 15%, molten Cr26 can wet the ZTA ceramic surface, with a wetting angle of only 17.7°. Oxygen and iron atoms diffused into the transition layer to form a metallurgical bonding interface, which enhanced the interface bonding strength and brittleness. A combined supporting effect of the Cr26 matrix on the ZTA ceramic particles and protecting effect of the ZTA ceramic particles on the matrix during wear resulted in an improvement in wear resistance. The brittleness interface harmed the wear resistance at a higher load (2 kg and 3 kg). This indicates the ZTA ceramic particles has positive influence on the wear resistance of composites.

Combustion synthesis of TiC-based ceramic-metal composites with high entropy alloy binder

Ceramic-metal composites TiC–High-Entropy Alloy (HEA) CoCrFeNiMe (Me = Mn, Ti or Al) were first produced by combustion synthesis method. Self-sustained synthesis occurs due to heat release from exothermic reaction Ti + C = TiC; the binder content was varied between zero and 40–50 wt.%. The combustion velocity and temperature gradually decreased with increasing binder content. Resultant materials consist of TiC grains and two-phase (fcc and bcc) binder. Vickers microhardness (100 g) of compacted cermet materials with 30 wt.% of binder was in the range of 10–17 GPa and increased with increasing bcc to fcc ratio. Based on experimental results and thermodynamic calculations, the mechanism of microstructure formation in TiC–HEA cermets was suggested.

The manufacture and characterization of WC-(Al)CoCrCuFeNi cemented carbides with nominally high entropy alloy binders

Recently, there has been increasing interest in cemented tungsten carbide hardmetals and titanium carbonitride cermets with binders of multi-component alloys (≥4 elements) or high entropy alloys (≥5 principal elements in equimolar ratios). Property improvements have been reported, such as increased ambient and elevated temperature hardness, as well as greater oxidation resistance.This study has thoroughly investigated model cemented carbides manufactured using coarse WC with a binder content of 20 wt% (32–37 vol%) from three different (Al)CoCrCuFeNi high entropy alloys (HEAs) and at different carbon levels (low, medium and high).Binder alloys were manufactured by both planetary ball milling of elemental powder mixtures and gas atomizing. Sintering was performed in vacuum for 2 h at different temperatures between 1200 °C and 1500 °C. Post-HIP treatments were also applied in some cases as all systems were difficult to densify without residual porosity.Detailed analyses were performed on the as-manufactured binder alloys, sintered binder alloys (without WC) and the actual sintered cemented carbides (WC + HEA). Various analysis methods were used to examine the materials. These included thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) to determine the melting behaviour; X-Ray Diffraction (XRD), Electron Backscatter Diffraction (EBSD) and Energy-Dispersive X-Ray Spectroscopy (EDS) to identify the type, crystal structure and exact composition of the phases present; and light optical microscopy (LOM) and scanning electron microscopy (SEM) for microstructural characterization. Additionally, the hardness and Palmqvist indentation toughness of each composition were also measured.2-Phase WC-HEA microstructures could not be obtained using the investigated high entropy alloys. Several solid solution binder alloys and numerous carbide phases were present after sintering, formed by segregation and reaction. The type and quantity of the phases depend on the carbon balance. For the compositions containing aluminium, it was found that aluminium forms oxides and intermetallic phases during sintering. The paper presents these findings in detail.

Structure and high temperature wear characteristics of CVD coating on HEA-bonded cermet

Ti(C,N)-based cermets with a CoCrFeMnNi high-entropy alloy (HEA) binder phase were coated via chemical vapor deposition (CVD). The influence of the HEA-bonded cermet substrate on the microstructure, orientation, adhesion, and high temperature frictional wear performance of the CVD coating was investigated. The results indicate that the HEA binder phase inhibits the growth of cermet grains and provides more nucleation sites for the coating. Thus, the coating on the HEA-bonded cermet has a smaller grain size. The substitution of HEA for the Ni binder phase increases the entropy value of the cermet system, resulting in a decrease in free energy. In the early stage of CVD, the gas atoms adsorbed on the solid surface with low free energy are in a more stable thermodynamic state, which enhances the adhesion strength between the coating and substrate. During high temperature frictional wear, the friction coefficient of the coating on Ni-bonded cermet is less than that of the coating on HEA-bonded cermet because of iron oxide lubricating films. However, the wear rate exhibits a reverse trend. The coating on the HEA-bonded cermet has the best wear resistance due to small grain size, superior hardness and excellent adhesion strength. The wear forms present in the CVD coatings are abrasive wear, adhesive wear and oxidation wear.

Synthesis of TiC–NiCrBSi Binder Alloy Composite Powders for Cladding and Deposition of Wear-Resistant Coatings

TiC–NiCrBSi binder metal matrix composites are fabricated by self-propagating high-temperature synthesis (SHS) in reaction powder mixtures of titanium, carbon (carbon black), and NiCrBSi alloy. It is established that stable combustion in a steady-state mode is possible with the content of a thermally inert metal binder in reaction mixtures up to 50%. Porous SHS cakes are crushed easily for subsequent separation by screening the composite-powder fraction necessary for the coating deposition. The synthesis products are studied by optical and scanning electron microscopy, X-ray diffraction (XRD), and electron probe microanalysis (EPMA). It is found that the average size of carbide inclusions in the composite structure depends on the content of thermally inert alloy powder in reaction mixtures and can be intentionally controlled in a wide range. The microhardness of granules of the composite powder formed by crushing SHS cakes decreases monotonically with an increase in the content of the metal binder softer than titanium carbide. The crystal lattice parameter of titanium carbide determined by XRD turned out considerably smaller than known values for equiatomic titanium carbide. It is established using local EPMA of carbide inclusions in the composite structure that the carbon-to-titanium weight ratio is 0.21 instead of 0.25 for equiatomic titanium carbide. Iron and silicon concentrations in carbide are negligibly low, those of oxygen and nickel are lower than 1%, and that of chromium is 2.5 wt %. It is concluded based on the analysis of the known data on the influence of all listed impurities on the titanium carbide lattice that the deficit of carbon is the main cause of a decrease in the lattice parameter.

Effects of binders on the microstructures and mechanical properties of ultrafine WC-10%AlxCoCrCuFeNi composites by spark plasma sintering

Ultrafine WC cemented carbides with 10 wt% mechanically alloyed AlxCoCrCuFeNi (x is the aluminium content in molar ratio and ranges from 0 to 1.5) high-entropy alloy (HEA) binders were fabricated by spark plasma sintering. The influences of the HEA binders on the microstructures and mechanical properties of WC-HEA cemented carbides were discussed. Due to the sluggish diffusion effect of the HEA binders, the WC grain growth activation energy of WC-HEA cemented carbides is significantly higher than that of WC-Co alloy. Consequently, the grain growth of WC is inhibited during sintering, and an ultrafine microstructure can be obtained. With increasing Al content of HEA binders, both the relative density of WC-HEA cemented carbides and the hardness of HEA binders increase, which contributes to the high hardness of WC-HEA cemented carbides. The fracture toughness of WC-HEA cemented carbides is codetermined by the wettability of HEAs on WC and the intrinsic sintering property and deformability of HEA binders. Therefore, the WC-HEA cemented carbide with 10 wt% Al0.5CoCrCuFeNi high-entropy alloy binder exhibits the best combination of Vickers hardness and fracture toughness, which are 2071 ± 6 HV30 and 10.3 ± 0.1 MPa m1/2, respectively.

Additive Manufacturing of Cemented Tungsten Carbide with a Cobalt-Free Alloy Binder by Selective Laser Melting for High-Hardness Applications

Cemented tungsten carbide (WC) is commonly used for wear-resistant applications, such as cutting tools and abrasives due to its extremely high hardness. This hardness leads to post-process machining of WC to be time- and cost-intensive. This study examined the feasibility of additive manufacturing of cemented WC to near-net-shape in an effort to reduce post-process machining. The binder phase in the manufactured samples is an iron-based alloy, which has a lower melting temperature than cobalt, the conventional binder in cemented WC. In this proof-of-concept study, cuboid specimens of WC with a low content of the iron-based alloy binder were printed; the effect of different processing conditions on the resultant density and microstructure of the material were investigated. Theoretical densities as high as 95% were achieved using this method. Artifacts indicative of the manufacturing process are present in the samples, and the challenges in removing the processing history from the final microstructure are discussed.

SHS of “TiC – NiCrBSi binder” composite powders

Phase composition and structure of “TiC-NiCrBSi alloy binder” metal matrix composite powders have been investigated. The composites were synthesized from titanium, black carbon and Ni77Cr15Si3B2 alloy reaction powder mixtures by self-propagating high temperature synthesis (SHS). The composite powders were produced by crushing of SHS cakes. A size of TiC inclusions in NiCrSiB matrix depends on the content of NiCrBSi in the reactive powder mixtures and varies from 7.3 to 1.2 μm.

Nanoengineering of metallic alloys for machining tools: Multiscale computational and in situ TEM investigation of mechanisms

Influence of carbon nanotubes (CNT), hexagonal boron nitride (h-BN) and tungsten carbide (WC) nano-reinforcement on the mechanical and tribological properties of the Cu-Ni binder alloy was investigated experimentally and numerically. In situ TEM and multiscale micromechanical finite element (FE) modeling were used to study the mechanisms of deformation of the nanomodified binder. Сomplex reinforcement by 0.1% CNT + 0.1% hBN + 0.69% WC increases the tensile strength of the materials from 155 to 346 MPa, bending strength from 420 to 832 MPs, hardness from 2.1 to 2.4 GPa and elastic modulus from 98 to 123 GPa. The complex reinforcement changes the wear mechanism and significantly enhanced the tribological properties of the binders, decreasing the coefficient of friction from 0.47 to 0.28 and wear rate from 12.3 to 6.7·10−6 mm3/N/m. The failure of the nanomodified binder was found to be caused by the emergence and propagation of microcracks along the interface between hBN particles and the matrix. Carbon nanotubes inhibit the propagation of cracks, significantly increasing the mechanical and tribological properties of Cu-Ni binders.

Corrosion mechanism of HVOF thermal sprayed WC-CoCr coatings in acidic chloride media

HVOF thermal sprayed WC cermet coatings exhibit excellent abrasive and erosive wear resistance due to the presence of high volume fraction of WC particles bounded by a tough cobalt or cobalt-chromium alloy binder. However, less information is at present available on the corrosion response of these coatings in strong acidic environment. In this study, the corrosion behaviour of the HVOF WC-CoCr coatings was investigated by electrochemical polarization technique in 0.1 N hydrochloric (HCl) acid solution at 25 °C. The coating morphology was studied by scanning electron microscopy (SEM) and the relationships between the microstructure and corrosion mechanism were investigated using small-angle X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy measurements. The analysis of the corroded coating surface showed that during anodic polarization, the corrosion attack of the WC-CoCr coating began with active oxidation of the binder phase followed by the formation of a pseudo-passive layer composed by anhydrous Cr-oxides (CrO), Co-oxides (CoO/Co3O4) and W-oxides (WO3). At higher potentials the corrosion was governed by the hydration of tungsten oxide (WO3·xH2O) and the extension of the oxidation to the WC particles.

High entropy alloys: Substituting for cobalt in cutting edge technology

Cemented carbide, also known as hard metal, is one of the most outstanding composite engineering materials since its commercial introduction in the 1920s. The unique combination of strength, hardness and toughness makes cemented carbides highly versatile materials for the most demanding engineering applications. In their simplest form, these materials are composites of tungsten carbide (WC) grains that are cemented with a ductile metallic binder phase, typically cobalt. However, despite the superiority of Co as binder material, there is a long-standing need to find alternative binders due to serious health concerns that have haunted the industry for nearly 80 years. In the present study, we develop a new cemented carbide with a high entropy alloy binder phase (CoCrFeNi) from raw materials to a fully functional, coated and gradient-sintered cutting tool insert. The new hard metal with reduced Co content is designed by using first principles theory and the CALPHAD method. The cutting tool was made by pressing the new hard metal in a standard geometry, sintered to have a thin binder phase enriched surface zone, free from cubic carbides and coated with protective layers of Ti(C,N) and Al2O3. The resulting cutting insert was tested in a real machining operation and compared to a state-of-the-art reference that had Co as binder phase. The cutting tool made of the newly developed cemented carbide has an exceptionally high resistance against plastic deformation at all tested cutting speeds in the machining test, outperforming the reference insert, which shows a linear increase in edge depression when the cutting speed is increased. This result opens up the possibility to utilize the unique properties of high entropy alloys for industrial applications, in particular, as binder phase in new cemented carbides.

Sintering of tungsten carbide cermets with an iron-based ternary alloy binder: Processing and thermodynamic considerations

Cemented tungsten carbide materials are traditionally bonded using a cobalt matrix, resulting in a material that possesses a unique combination of exceptional properties. However, cobalt has been recently classified as “reasonably anticipated to be a human carcinogen,” and thus, removal of this hazardous phase is desired for many applications. This research focuses on the production of tungsten carbide bodies cemented with a non-hazardous iron-based alloy binder phase. This binder has roots in the previous transition metal binders and additives for tungsten carbide and is based on the principles of high-entropy alloys; however, it relies on a novel means of carbide formation and dispersion from prior investigations. Sintering studies were conducted through uniaxial hot pressing, field-assisted sintering techniques, and pressureless sintering techniques. While some of the results of hot pressing and field-assisted sintering technique were positive, the resultant mesostructure exhibited an undesired, graded, heterogeneous form. Pressureless sintering, on the other hand, was capable of producing a homogeneous microstructure with high theoretical density along with promising hardness and indentation toughness values.

Design of cemented tungsten carbide and boride-containing shields for a fusion power plant

Results are reported on cemented tungsten carbide (cWC) and boride-containing composite materials for the task of shielding the centre column of a superconducting tokamak power plant. The shield is based on five concentric annular shells consisting of cWC and water layers of which the innermost cWC shield can be replaced with boride composites. Sample materials have been fabricated changing the parameters of porosity P, binder alloy fraction fbinder and boron weight fraction fboron. For the fabricated materials, and other hypothetical samples with chosen parameters, Monte Carlo studies are made of: (i) the power deposition into the superconducting core, (ii) the fast neutron and gamma fluxes and (iii) the attenuation coefficients through the shield for the deposited power and neutron and gamma fluxes. It is shown that conventional Co-based cWC binder alloy can be replaced with a Fe–Cr alloy (92 wt.% Fe, 8 wt.% Cr), which has lower activation than cobalt with minor changes in shield performance. Boride-based composite materials have been prepared and shown to give a significant reduction in power deposition and flux, when placed close to the superconducting core. A typical shield of cemented tungsten carbide with 10 wt.% of Fe–8Cr binder and 0.1% porosity has a power reduction half-length of 0.06 m. It is shown that the power deposition increases by 4.3% for every 1% additional porosity, and 1.7% for every 1 wt.% additional binder. Power deposition decreased by 26% for an initial 1 wt.% boron addition, but further increases in fboron showed only a marginal decrease. The dependences of power deposited in the core, the maximum neutron and gamma fluxes on the core surface, and the half attenuation distances through the shield have been fitted to within a fractional percentage error by analytic functions of the porosity, metallic binder alloy and boron weight fractions.

Dynamic hardness of cemented tungsten carbides

Cemented tungsten carbides are composed of a hard tungsten carbide (WC) phase held together by a soft, ductile binder phase, typically cobalt (Co). This study examines the role of the binder composition and content on the Knoop hardness at quasi-static and dynamic strain rates. Seven different tungsten carbide materials were tested: four WC-Co systems containing 10%, 15%, 20% and 25% cobalt, two with a chromium‑nickel alloy binder phase, and one “binderless” tungsten carbide. Quasi-static Knoop hardness testing was performed at strain rates of 10−3 s−1 and at indentation loads between 300 and 30,000 g using a Wilson Tukon 2100 unit. Dynamic Knoop hardness testing was conducted at strain rates of 103 s−1 using a Dynamic Indentation Hardness Tester over a range of indentation loads. All of the materials exhibited a rate-dependent Knoop hardness, with the hardness increasing by up to 60% with increasing strain rate.

Consolidation of Sm2Fe17N3 magnets with Sm-based eutectic alloy binder

Consolidation of Sm2Fe17N3 powder with a new Sm-based alloy as a metal binder was examined. Investigation of various Sm-based alloys led to the discovery of a Sm-Fe-Cu-Al alloy having a low melting point of 495 °C, which is more than 100 °C lower than the thermal decomposition temperature of Sm2Fe17N3. The metallographic structure of the Sm-Fe-Cu-Al alloy ingot was a SmCu/Sm eutectic structure containing solid-solution Fe, Cu and Al. Pulverized Sm-Fe-Cu-Al powder as a binder was mixed with Sm2Fe17N3 powder, and the mixture was hot-pressed by a current sintering apparatus. The Sm-Fe-Cu-Al alloy binder did not affect the magnetization of Sm2Fe17N3 adversely after consolidation. The binder-added Sm2Fe17N3 hot-pressed compacts successfully maintained the coercivity of the raw powder over a wide range of hot-pressing temperatures, whereas additive-free Sm2Fe17N3 hot-pressed compacts showed a significant decrease in coercivity. Therefore, the Sm-Fe-Cu-Al alloy binder overcame the weakest point of Sm2Fe17N3 magnets. XRD analysis suggested that the Sm-Fe-Cu-Al binder restrained precipitation of the α-Fe phase, which is thought to be the probable cause the decrease of coercivity.

A Polymer-Alloy Binder for Structures-Properties Control of Battery Electrodes

The microstructures of electrodes play a critical role in controlling the charge transport in electrode composites. Achieving uniform and stable microstructures for battery electrodes with aid of binder materials is an important task in battery research. Here, we propose a polymer alloy binder rich in amorphous structures to address that need. This alloy binder is fabricated by complexing poly(vinylidene fluoride) and ultra-high molecular weight poly(ethylene oxide). Due to a good compatibility of the two polymers and the ultra-long chain of poly(ethylene oxide), the crystallization of each component is greatly suppressed and more amorphous phase is achieved. The amorphous structure of the alloy binder can dramatically improves the adhesion properties (by ca. 150%), structure uniformity and interface stability of the final electrode simultaneously, as compared with the electrodes with a traditional PVDF binder. As a result, the mechanical flexibility, electrolyte wettability, the electron/ion transport and electrochemical performance of the final electrodes are notably improved as compared with pure PVDF binder. This study brings about a cost-effective binder solution based on polymer alloys for controlling the microstructures/interfaces and properties of battery electrodes.