Cobalt Matrix Research Articles

Investigating phase and magnetic properties in Co-2 wt.% MWCNT nano-composites prepared by mechanical alloying

MWCNT nano-composites with a cobalt content of 2 weight percent were created by mechanically alloying during different times. Modern techniques, including x-ray diffraction (XRD), differential thermal analysis (DTA), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and superconducting quantum interference device (SQUID), were used to examine the effects of CNT addition on the Co morphology and magnetic characteristics of the samples. It was shown that the characteristics of Co in 2 weight percent MWCNT nano-composites were retained in a sample that was milled for 60 min. Agglomerates of nanoparticles were the end result, with CNTs evenly distributed throughout the cobalt matrix 60 min after mechanical alloying. Analysis of magnetic hysteresis loops revealed that the inclusion of CNTs altered the magnetic characteristics of nano-composite samples. Analysis of magnetic hysteresis loops revealed that the inclusion of CNTs altered the magnetic characteristics of nano-composite samples. The well-developed interfacial structure in this work significantly improved the cobalt-MWCNT nano-composites’ magnetic characteristics.

Critical review of metal-ceramic composites fabricated through additive manufacturing for extreme condition applications

Metal-Ceramic composites are a special class of materials, including elements as matrix and reinforcements. These composites, especially metal matrix composites, are of great significance in several high-end engineering applications due to their tunable conductivity, strength, and toughness. This review paper summarizes studies carried out to fabricate metal-ceramic composites by additive manufacturing. Various metal matrix composites such as titanium matrix composites, cobalt matrix composites, iron matrix composites, nickel matrix composites, and aluminum matrix composites are elaborated in detail. The paper provides an in-depth analysis of applications, trends, opportunities, and outlook for additive manufacturing of Metal-Ceramic composites.

Laser additive manufacturing of a CoCr-based medium-entropy alloy: Impressive stacking fault-induced nanotwinning strengthening through rapid solidification

The directed energy deposition (DED) technique was used to deposit a CoCrNiWC medium entropy alloy (MEA) through a robotic-assisted laser additive manufacturing (LAM) machine. The microstructural features, including solidification grains, structural defects, and phase transformations, along with uniaxial tensile behavior in different orientations, were comprehensively studied. Furthermore, a quantitative assessment was carried out to evaluate the contribution of strengthening mechanisms through apprising stacking fault constant of 11362 MPa nm for the developed MEA, enrolling the impact of FCC to HCP crystal structure transition for the cobalt matrix after rapid cooling LAM solidification in the solid-state board. In addition, the presence of numerous ordinary screw dislocations interacting with each other, stacking faults (SFs), nanotwins, and refined grains led to their hindering as the critical factor for strengthening. The SF intersections resulted in the formation of effective Lomer-Cottrell (LC) locks and nanotwins, which were barriers to slip and attributed to dislocation interactions. Accordingly, the rapid cooling solidification of the LAM process contributed to impressive mechanical properties of deposited CoCr-based MEA with remarkable yield and tensile strengths of ∼895 and 1410 MPa, confirming the direct contributions of statistically stored dislocations upon impact SF and nanotwining strengthening.

Designing Multifunctional Multiferroic Composites for Advanced Electronic Applications

This paper presents a novel approach for the fabrication of magnetoelectric composites aimed at enhancing cross-coupling between electrical and magnetic phases for potential applications in intelligent sensors and electronic components. Unlike previous methodologies known for their complexity and expense, our method offers a simple and cost-effective assembly process conducted at room temperature, preserving the original properties of the components and avoiding undesired phases. The composites, composed of PZT fibers, cobalt (CoFe2O4), and a polymeric resin, demonstrate the uniform distribution of PZT-5A fibers within the cobalt matrix, as demonstrated by scanning electron microscopy. Detailed morphological analyses reveal the interface characteristics crucial for determining overall performance. Dielectric measurements indicate stable behaviors, particularly when PZT-5A fibers are properly poled, showcasing potential applications in sensors or medical devices. Furthermore, H-dependence studies illustrate strong magnetoelectric interactions, suggesting promising avenues for enhancing coupling efficiency. Overall, this study lays the basic work for future optimization of composite composition and exploration of its long-term stability, offering valuable insights into the potential applications of magnetoelectric composites in various technological domains.

Developing high strength and ductility in cobalt alloy via chromium carbonitride addition

In this study, we present a strategy for the development of cobalt alloy with high performance, by introducing a nitrogen-containing solid solution powder Cr2(C,N). Despite the cobalt accelerates the nitrogen removal from Cr2(C,N) during sintering, interestingly, nitrogen seemingly plays a pivotal role in regulating the microstructure of cobalt alloy. Detailed microstructural analyses indicate that the fcc-Co increase, CrN precipitates and finer grain size are formed within the cobalt matrix with Cr2(C,N) addition. These structural modifications significantly contribute to the strength and toughness. In comparison to the without N-doped cobalt alloy, the compressive strength undergoes a significant 34% increase, rising from 1150 MPa to 1540 MPa. Similarly, the bending strength exhibits an upward trend, ascending from 1605 MPa to 1766 MPa. Concurrently, the introduction of Cr2(C,N) results in an almost 80% enhancement in bending strain compared to the without N-doped one. Additionally, a notable 28% increase in hardness is obtained. The substantial enhancements in strength and toughness are mainly attributed to the combined effects of solid solution and precipitation strengthening. Our findings confirm the capability of Cr2(C,N) to the cobalt alloy reinforcement, providing valuable insights for integrating Cr2(C,N) to enhance the cobalt alloy, and laying a foundation for future investigations into the forms of nitrogen and the strengthening and toughening mechanisms of nitrogen-containing alloy. The insights gained in this study also provide novel strategies for the design of materials characterized by both needed strength and ductility, thereby advancing the development of ultra-strong and ductile materials with superior toughness.

Effect of heat treatment on microstructure and wear properties of laser additively manufactured 316 L stainless steel/Co-Cr-W alloy part using directed energy deposition method

The directed energy deposition additive manufacturing was applied to fabricate hard Co-Cr-W layers on the 316 L stainless steel substrate. The effect of different heat treatment cycles was investigated. The primary microstructure of deposited layers contained a cobalt matrix with interdendritic eutectic carbides mainly M7C3, M23C6, and M6C. Most of the primary carbides were dissolved in the matrix after the solution treatment at 1250 °C for 1 h. The aging treatment promoted the precipitation of (W/Co)6C carbides. The hard carbides caused the third-body wear and increased the wear volume loss of specimens. The solution & double aging treatment provided the optimum combination of hardness and wear resistance due to the best distribution of W/Co carbide. The wear volume loss after heat treatment was decreased from about 6.6 mm3 to 2.8 mm3 compared to the as-deposited specimen. The proposed solution & double aging heat treatment improved wear resistance by 50%.

Insights into the activation of peroxymonosulfate by ZIF-L@ZIF-67 derived CoCN catalyst for highly effective removal of phenol in the presence of chloride ions

A novel catalyst with cobalt and nitrogen-codoped porous carbon matrix (CoCN-900) was successfully prepared, characterized and applied for activating peroxymonosulfate (PMS) to remove phenol in aqueous solution. The CoCN-900 material exhibited superior performance in activating PMS for phenol degradation and could completely remove phenol within 60 min. Radical quenching tests and electron paramagnetic resonance (EPR) analysis showed that 1O2 and SO4•– played a major role in the phenol removal process over the CoCN-900/PMS system. In addition, the influences of catalyst/PMS dose, initial phenol concentration, reaction temperature, natural organic matter and coexisting anions on phenol degradation were systematically investigated. Particularly, it was found that the chloride ions (Cl–) had a significant accelerative effect, increasing the phenol degradation rate from 0.142 to 0.600 min−1. In the presence of Cl–, the phenol degradation efficiency was primarily ascribed to the effects of 1O2 and O2•–, which were significantly different from those in the absence of Cl–. Meanwhile, Cl– could also accelerate the deactivation of the catalyst. Findings in this study provided new insight for the fabrication of high-performance zeolitic imidazolate frameworks (ZIFs)-derived carbon materials and evaluating the influences of anions on the degradation of phenolic contaminants in PMS-based advanced oxidation processes (AOPs).

Topology of WC/Co Interfaces in Cemented Carbides.

WC-Co cemented carbides build one of the important classes of metal matrix composites. We show in this paper that the use of machine vision methods makes it possible to obtain sufficiently informative statistical data on the topology of the interfaces between tungsten carbide grains (WC) and a cobalt matrix (Co). For the first time, the outlines of the regions of the cobalt binder were chosen as a tool for describing the structure of cemented carbides. Numerical processing of micrographs of cross sections of three WC-Co alloys, which differ in the average grain size, was carried out. The distribution density of the angles in the contours of cobalt "lakes" is bimodal. The peaks close to 110° (so-called outcoming angles) correspond to the contacts between the cobalt binder and the WC/WC grain boundaries. The peaks close to 240° (or incoming angles) correspond to the WC "capes" contacting the cobalt "lakes" and are determined by the angles between facets of WC crystallites. The distribution density of the linear dimensions of the regions of the cobalt binder, approximated with ellipses, were also obtained. The distribution density exponentially decreases with the lengths of the semi-axes of the ellipsoid, approximating the area of the cobalt binder. The possible connection between the obtained data on the shape of cobalt areas and the crack trajectories in cemented carbides is discussed.

Nanocomposite Co-nSiC coatings electrodeposited from cobalt-gluconate bath via pulse reverse plating technique with anionic surfactant

The co-deposition of silicon carbide nanoparticles (50 ± 5 nm diameter) in an electrodeposited metallic cobalt matrix has been investigated under pulse reverse plating (PRP) conditions with the inclusion of an anionic surfactant. The effect of variable anionic surfactant content in the plating solution with a particle content of 5 g L−1 was evaluated using both direct current (DC) plating and PRP. The particle content of the coatings was investigated by varying the cathodic cycle during PRP by varying the cathodic cycle time between 30 and 240 s per pulse whilst maintaining a fixed anodic charge. The coatings were assessed by SEM and EDX in cross section to determine the effect of PRP parameters and anionic surfactant content on the particle content of. With no anionic surfactant, all coatings produced contained a similar particle content. Addition of anionic surfactant affected the SiC content of DC and PRP coatings. PRP combined with anionic surfactant to produce an electrophoretic nanoparticle delivery mechanism increasing the SiC content of coatings compared to DC coatings. Higher SiC content was observed at shorter cathodic cycle times.

The effect of small additions of Nb and Ti on the sliding wear behavior of a Co–30Cr–5Mo alloy

This work studies the addition of 0.5%Nb and 0.5%Ti in a Co–30Cr–5Mo alloy as well as the increase of carbon from 0.1 to 0.3%. The main goal is to increase the wear resistance of the alloy with such additions due to the formation of primary carbides (TiC and NbC). The additions of carbon, niobium and titanium were as ferroalloys, which implies the addition of iron into the chemistry of the alloy. Microstructural prediction studies by JMatPro indicate that the addition of all of these elements promotes an increase in the amount of the sigma phase, an undesirable phase because it is a hard brittle intermetallic compound. However, this undesirable phase could be eliminated from the structure by means of a solubilization heat treatment undertaken at 1200 °C for 2 h; this heat treatment lowered the values of hardness of the alloys. An additional aging heat treatment promoted the precipitation of chromium carbides of the type M23C6 as dispersed elongated bars within the cobalt matrix, which notably increased the hardness of the alloys. Each alloy was wear tested under two loads 52 and 78 N and under dry sliding and also under lubricated sliding using Hank solution as lubricant; the tests were undertaken at a sliding speed of 0.5 m/s. Results indicate that the addition of Ti and Nb produced small amounts of TiC and NbC in addition to a light increase in the amount of the sigma phase which increased hardness in the as-cast conditions. These alloys, with Ti and Nb additions, shown the higher hardness values in the as-aged conditions. The wear resistance of the alloys are in agreement with the hardness results particularly for the dry sliding tests. Wear resistance was higher for the harder alloys (those with Nb and Ti additions in the as-aged conditions) and it is lower for the higher applied load. For the case of the lubricated wear tests, such a trend is also observed but not so clearly as for the unlubricated tests. However, friction and wear for the lubricated experiments shown values extremely low compared to these observed for the unlubricated sliding wear tests.

Phenomenological Model of Cavitation Erosion of Nitrogen ION Implanted Hiped Stellite 6

Abstract Stellites are a group of Co-Cr-C-W/Mo-containing alloys showing outstanding behavior under cavitation erosion (CE) operational conditions. The process of ion implantation can improve the CE resistance of metal alloys. This work presents the elaborated original phenomenological model of CE of nitrogen ion implanted HIP-consolidated (Hot Isostatically Pressed) cobalt alloy grade Stellite 6. The ultrasonic vibratory test rig was used for CE testing. The nitrogen ion implantation with 120 keV and fluence of 5 × 1016 N+/cm−2 improves HIPed Stellite 6 cavitation erosion resistance two times. Ion-implanted HIPed Stellite 6 has more than ten times higher CE resistance than the reference AISI 304 stainless steel sample. Comparative analysis of AFM, SEM and XRD results done at different test intervals reveals the kinetic of CE process. The model includes the surface roughness development and clarifies the meaning of cobalt-based matrix phase transformations under the nitrogen ion implantation and cavitation loads. Ion implantation modifies the cavitation erosion mechanisms of HIPed Stellite 6. The CE of unimplanted alloy starts on material loss initiated at the carbides/matrix interfaces. Deterioration starts with cobalt matrix plastic deformation, weakening the carbides restraint in the metallic matrix. Then, the cobalt-based matrix and further hard carbides are removed. Finally, a deformed cobalt matrix undergoes cracking, accelerating material removal and formation of pits and craters’ growth. The nitrogen ion implantation facilitates ɛ (hcp—hexagonal close-packed)) → γ (fcc—face-centered cubic) phase transformation, which further is reversed due to cavitation loads, i.e., CE induces the γ → ɛ martensitic phase transformation of the cobalt-based matrix. This phenomenon successfully limits carbide removal by consuming the cavitation loads for martensitic transformation at the initial stages of erosion. The CE incubation stage for ion implanted HIPed Stellite 6 lasts longer than for unimplanted due to the higher initial content of γ phase. Moreover, this phase slows the erosion rate by restraining carbides in cobalt-based matrix, facilitating strain-induced martensitic transformation and preventing the surface from severe material loss.

Manufacturing of WC-17Co 3D-objects by Laser Powder Bed Fusion followed by heat-treatment

Conventional tungsten carbide (WC) cermet parts containing a cobalt matrix phase are generally produced via powder sintering. In this study it is shown that cermet parts can also be produced by laser powder bed fusion from WC-17Co powder precursor. Optimal process parameters were found for manufacturing without preheated building plate. Micro-structural analysis revealed noteworthy porosity fraction (1.41%) as well as the presence of small-scale cracks in the as-built specimens. It is further shown that most of these defects can be eliminated by heat treatment at ambient pressure or by hot isostatic pressing. Heat treatment also led to the dissolution of the fragile W2C phase. Hardness test results indicate that the performance of the AM parts was comparable to that of a reference produced via powder sintering. The work is a successful demonstration of manufacturing of cermet parts using laser powder bed fusion.

Nanostructuring Effect of Nano-CeO2 Particles Reinforcing Cobalt Matrix during Electrocodeposition Process.

The electrodeposition method was used to obtain nanostructured layers of Co/nano-CeO2 on 304L stainless steel, from a cobalt electrolyte in which different concentrations of CeO2 nanoparticles (0, 10, 20, and 30 g/L) were dispersed. The electrodeposition was performed at room temperature using three current densities (23, 48, and 72 mA cm−2), and the time was kept constant at 90 min. The influence of current densities and nanoparticle concentrations on the characteristics of the obtained nanostructured layers is also discussed. An X-ray diffractometer (XRD) was used to investigate the phase structure and cobalt crystallite size of the nanostructured layers, and a contact angle (sessile drop method) was used to assess the wettability of the electrodeposited layers. The roughness of the surfaces was also studied. The results show that the nanostructured layers became more hydrophilic with increasing nanoparticle concentration and increasing current density. In the case of pure cobalt deposits, an increase in the current density led to an increase in the size of the cobalt crystallites in the electrodeposited layer, while for the Co/nano-CeO2 nanostructured layers, the size of the crystallites decreased with increasing current density. This confirms the nanostructuring effect of nano-CeO2 electrocodeposited with cobalt.

The Effect of Nano-ZrO2 Dispersed Phase into Cobalt Plating Electrolyte on Layer Thickness and Current Efficiency

The aim of this work is to obtain nanocomposite layers having a cobalt matrix with zirconium oxide nanoparticles (mean diameter 30 nm) through the electrodeposition process. The plating electrolyte suspension is prepared by adding ZrO2 nanoparticles in a sulfate-chloride cobalt electrolyte at a concentration of 0 and 10 g·L−1. The electrodeposition is performed at room temperature, using three current densities of 23, 48 and 72 mA·cm−2 and three deposition times of 30, 60 and 90 min. The influence of current density, time and nanoparticles concentrations on the characteristics of the obtained nanostructured layers are also discussed. ZrO2 ceramic nanoparticles as a dispersed phase in the cobalt deposition electrolyte modify the mechanism of its electro-crystallization, so they participate in this process by increasing the rate of cobalt deposition, confirmed by the thickness of the nanocomposite layers obtained. The paper presents some of the comparative results obtained regarding the thickness of the layers, the current efficiency and the inclusion of the nanoparticles into nanocomposite layers depending on the current density and time of the electrodeposition process. The analysis of Co/nano-ZrO2 nanocomposite layers with the help of optical light microscopy and electronic microscopy in cross-section highlights the good degree of adhesion of the layers to the metallic substrate made of 304L stainless steel. The results of the study show that as the current density and time increase, the thickness of the composite layers increases. The efficiency of the process is improved compared to the electrodeposition of pure cobalt layers. The degree of inclusion of ZrO2 nanoparticles increases with time and decreases with increasing of imposed current density on the electrodeposition process. The distribution of the dispersed phase in the cobalt metallic matrix is uniform. The layers obtained in this study can be applied in aircraft technology, in the automotive industry, as well as in biomedical applications in order to improve the properties and to increase the corrosion or tribocorrosion resistance in a specific environment.

Performance testing of supercoarse sintered carbides with alternative nickel-based matrices in the context of mechanical, tribological, thermal and metallographic investigations

The recent advances in rock, coal, gas and oil drilling under continuously increasing loads and increased cutting speeds motivate the interest in and development of coarse and supercoarse sintered carbides. Complex drilling conditions are best simulated during in-service tests but their objectiveness and reliability are often problematic. Therefore, performance testing of real cutting tools in controlled conditions is of great importance. New grades of supercoarse hardmetals with nickel-based binders and relevant mining tools were designed and manufactured. Performance tests consisting in controlled rotary mining of a homogeneous artificial mineral block showed significantly lower wear of the experimental sinters (24–69%) in comparison with the classical cobalt matrix counterpart. The performed mechanical, tribological, thermal, fractographic and substructural investigations revealed the wear micromechanism, the correlations between the results obtained as well as the factors of the increased tool performance.

Chemical and Structural Analysis of Newly Prepared Co-W-Al Alloy by Aluminothermic Reaction.

This article is devoted to the characterization of a new Co-W-Al alloy prepared by an aluminothermic reaction. This alloy is used for the subsequent preparation of a special composite nanopowder and for the surface coating of aluminum, magnesium, or iron alloys. Due to the very high temperature (2000 °C–3000 °C) required for the reaction, thermite was added to the mixture. Pulverized coal was also added in order to obtain the appropriate metal carbides (Co, W, Ti), which increase hardness, resistance to abrasion, and the corrosion of the coating and have good high temperature properties. The phase composition of the alloy prepared by the aluminothermic reaction showed mainly cobalt, tungsten, and aluminum, as well as small amounts of iron, titanium, and calcium. No carbon was identified using this method. The microstructure of this alloy is characterized by a cobalt matrix with smaller regular and irregular carbide particles doped by aluminum.

Synthesis and densification of (Zr-Hf-Nb-Ta)C-Co high entropy cermet prepared by pressureless melt infiltration using spark plasma sintering

Novel (Zr-Hf-Nb-Ta)C-xCo (x = 5, 10, 20 wt%) high entropy cermets (HEC4-Co) were successfully synthesized and densified using a simple two-step high temperature process. The high entropy carbide was first synthesized by solid state reaction at 1800 ℃ of a mixed powder compact. The reacted and partially sintered compact was then pressureless melt infiltrated with cobalt at 1600 ℃. The results show that degassing of the powders in the first step, before the infiltration step, significantly reduced the defects in the cermets. The HEC4-Co cermets consisted of a single-phase high entropy carbide (Zr-Hf-Nb-Ta)C in a single-phase cobalt matrix. The maximum hardness was achieved for a Co content of 10 wt%, 15.38 GPa (1569HV1), while the cermet with a Co content of 20 wt% had the highest indentation crack resistance, 9.72 MPa m1/2.

Integrating a 3D porous carbon fiber network containing cobalt with artificial solid electrolyte interphase to consummate advanced electrodes for lithium–sulfur batteries

Lithium-sulfur batteries (LSBs) are deemed as one of the most promising next-generation energy storage systems due to their high theoretical energy density. However, their intrinsic shortcomings hindered their practical commercialization. In this work, a powerful three-dimensional (3D) filter paper porous carbon decorated with cobalt (FPPC@Co) matrix is employed to fabricate high-quality anode and cathode simultaneously. Combining with in-situ surface engineering, the rationally designed solid electrolyte interphase @Li/FPPC@Co anodes can plate/strip Li uniformly without Li dendrites, manifesting a low overpotential of about 20 mV for 1000 h at 1 mA/cm2/1 mA h/cm2. COMSOL Multiphysics simulations further testify the underlying mechanisms. Meanwhile, with the help of molten sulfurizing method, the synthesized FPPC@Co/S cathode exhibits excellent stability with high capacity retention of 73.3% after 200 cycles at 1 C. Furthermore, we paired SEI@Li/FPPC@Co anode and FPPC@Co/S cathode to assemble lithium-sulfur full cells. The SEI@Li/FPPC@Co||FPPC@Co/S full cell shows superior electrochemical performance with a long-term cycle life (a capacity retention of 88.7% after 200 cycles at 1 C). Insight gained from this work opens a new door for fabrication of high-quality electrodes for LSBs.

Influence of spray distance on mechanical and tribological properties of HVOF sprayed WC-Co-Cr coatings

Abstract In this work, the tungsten carbide reinforcement in cobalt matrix (WC-Co-Cr) coatings was studied. The deposition process was carried out by high-velocity oxy-fuel spraying (HVOF). The study aimed to investigate the influence of one of the key process parameters, namely spray distance, on the coatings’ microstructure and phase composition, as well as their mechanical and tribological properties. The manufactured coatings were analysed by scanning electron microscopy, X-ray diffraction (XRD), instrumented indentation test, pull-off adhesion test and ball-on-disc method. The results revealed that selection of proper spray distance caused a high index of carbide retention (ICR) amounting to 0.95, which promoted higher hardness and better wear resistance. Instrumental microhardness was in the range of 14.2–14.8 GPa, whereas the Young modulus exhibited values from 336 GPa up to 342 GPa. The bond strength of deposited coatings was in the range of 55–65 MPa. Wear factor values were in the range of 73–81 × 10−7 mm3/(N · m) and the friction coefficient was about 0.4. The dominant wear mechanism is abrasion and adhesive mode supported by the fatigue-induced material delamination.

High-Temperature Wear Behavior of Cobalt Matrix Composites Reinforced by LaF3 and CeO2

High-Temperature Wear Behavior of Cobalt Matrix Composites Reinforced by LaF3 and CeO2