Cobalt-based Alloys Research Articles

Investigating magnetic properties of Co68Fe4B15Si13 amorphous alloy by molecular dynamics and DFT calculations

Cobalt-based amorphous alloys, in particular CoFeBSi, have been widely used to study the response of ac-impedance to the external dc magnetic field, i.e., the so-called Giant Magneto Impedance (GMI) effect. The utility of CoFeBSi in different applications such as field-sensitive sensors is known and practiced. Despite the wealth of experimental studies on GMI properties of CoFeBSi alloys, no computational approach has yet been addressed on electronic and magnetic properties of these systems at nanoscales. In this study, we have computed electronic and magnetic properties of amorphous CoFeBSi alloys using a combined Molecular Dynamics (MD) and Density Functional Theory (DFT) approach. MD is used to provide a physically realistic sampling of different atomic configurations while the properties such as dipole moments and magnetic susceptibilities are computed using DFT. Our study shows a wide spectrum of electronic as well as magnetic properties for nanoclusters of different sizes having implications for rational design of Co-based ferromagnetic alloys.

Laser Cladding of Ultra-Thin Nickel-Based Superalloy Sheets.

Laser cladding is a well-established process to apply coatings on metals. However, on substrates considerably thinner than 1 mm it is only rarely described in the literature. In this work 200 µm thin sheets of nickel-based superalloy 718 are coated with a powder of a cobalt-based alloy, Co–28Cr–9W–1.5Si, by laser cladding. The process window is very narrow, therefore, a precisely controlled Yb fiber laser was used. To minimize the input of energy into the substrate, lines were deposited by setting single overlapping points. In a design of experiments (DoE) study, the process parameters of laser power, laser spot area, step size, exposure time, and solidification time were varied and optimized by examining the clad width, weld penetration, and alloying depth. The microstructure of the samples was investigated by optical microscope (OM) and scanning electron microscopy (SEM), combined with electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDX). Similarly to laser cladding of thicker substrates, the laser power shows the highest influence on the resulting clad. With a higher laser power, the clad width and alloying depth increase, and with a larger laser spot area the weld penetration decreases. If the process parameters are controlled precisely, laser cladding of such thin sheets is manageable.

Perbandingan Hipersensitivitas Tipe IV Akibat Paparan Remanium Gm800 Dan Stainless Steel 316L

Stainless steel and cobalt chromium is a metal that is used in dentistry. Stainless steel (SS) 316L has good corrosion resistance, but there are still many cases of hypersensitivity due to the use of such materials. Remanium GM800 is a cobalt-based alloy which is relatively mild with the advantages of having a high fracture resistance, high modulus of elasticity and resistance to corrosion. The research aims to know type IV hypersensitivity reactions for cobalt chromium GM800 applications compared with 316L Stainless steel. The research was conducted through the test GPMT (Guinea Pig Maximization Test). The pre-research phase does CoCr patch/SS/control application to 3 guinea pigs of each group with concentrations of 5%, 10%, 20%, 40%, and 80%. Primary research begins with intradermal induction on the backs of guinea pigs for 7 days with a suspension of A (50% FCA emulsion dan 50% Propylene glycol), B (SS/CoCr/blank dan Propylene glycol) and C (50% SS/CoCr/blank suspension and 50% FCA) on the left and right backs of guinea pigs. On the 8th day induction results topical concentration of 40% for 24 hours, then opened to see the reaction and closed again for 48 hours. After that, the research was continued with challenge phase by attaching patch 5% concentration for 14 days. On the 28th day was observed erythema and edema on the skin of guinea pigs followed by sacrifice in order to obtain specimen to do immunohistochemical staining by ED antibodies. The result showed 316L SS cause 40% of the samples sensitized that were grouped in moderate classification, while CoCr GM800 cause 20% of the samples sensitized so classified in the mild classification in triggering type IV hypersensitivity reaction. Histopathology examination showed that 42% of the visual field SS 316L specimen expressed macrophages, while only 28% expressed macrophages in CoCr GM800 specimen. The conclusion of this study CoCr GM800 trigger type IV hypersensitivity reaction is lower than SS 316L.

Emission Spectrometric Evaluation of a Hollow-Cathode Glow Discharge Plasma with Helium–Oxygen Mixed Gas for Surface Modification of Co–Cr–Mo Alloy

This paper represents emission spectrometric analysis of a hollow-cathode glow discharge plasma with helium–oxygen mixed gas for surface treatment of a cobalt-based alloy, together with surface analysis of the resulting oxide layer. A Co–28Cr–6Mo alloy was employed as a specimen. The objective of this work is to obtain plasma information for the operating conditions to be optimized for producing a stoichiometric oxide layer on the alloy surface. Helium atomic lines, atomic and ionic lines of oxygen atom, and band heads of oxygen molecule ion were observed in the emission spectra. These intensities drastically changed depending on a mixing ratio of helium–oxygen mixed gas; particularly, the emission intensity of the molecular bands was largely enhanced in the mixed gas plasma compared to the pure oxygen plasma. This band spectrum is assigned to an electronic transition from the 4 Σ g to 4 Π u states of oxygen molecule ion, whose excitation energies are 18–19 eV from the ground state of oxygen molecule. It is thus suggested that a Penning-type ionization process with metastables of helium atom (1s2s 1 S 0, 20.6 eV and 3 S 1, 19.8 eV) is an excitation mechanism how the number density of the corresponding excited state can be elevated in the helium–oxygen mixed gas plasma. This effect, which more populated the excited oxygen species in the plasma, also exerted influence on the resultant oxide layer, such as the chemical composition and the layer thickness. Surface analysis by X-ray photoelectron spectroscopy indicated that an oxide layer consisting of iron and chromium oxides was formed by this plasma treatment, and that chromium atom was enriched in it. The thickness of the oxide layer varied with a mixing ratio of the plasma gas.

Annealing effect on the magnetic properties of cobalt-based amorphous alloys

The annealing effects on the magnetic properties of the Co72B19.2Si4.8Cr4 and Co64.8Fe7.2B19.2Si4.8Cr4 alloy systems are reported. Ribbon samples with 2 mm width and 20–30 μm thickness for both compositions were synthesized by melt spinning. The as-spun samples were subjected to annealing at various temperatures below their glass transition temperatures for 15 min in a vacuum. The annealed systems tended to have improved soft magnetic characteristics, including higher saturation magnetization and lower coercivity values, while maintaining their amorphous phase. A high saturation magnetization of 87.8 emu g−1 and low coercivity of 0.084 Oe were obtained for Co64.8Fe7.2B19.2Si4.8Cr4 after annealing at 400 °C, which is a significant improvement in comparison to the magnetic properties of the as-spun ribbons.

Effect of rare earth element on the oxidation behavior of novel γ/γ′-strengthened Co–9Al–10W alloys

Abstract

Nanoscale martensitic phase transition at interfaces in shape memory materials

In polycrystalline shape memory materials, mechanical interactions between martensitic transformation and grain boundaries at small scales play a critical role. Using a cobalt-based shape memory alloy, instrumented nanoindentation that probes nanoscale behavior reveals that grain boundary regions are resistant to transformation and have an adverse effect on shape memory possibly because an increase in strain energy outweighs reduction in interface energy. When grain boundaries are replaced by a thin, intergranular layer of a ductile and more malleable phase, grain boundary constraints are greatly alleviated, and transformation nearby can be well accommodated. Statistical analysis of results from a large number of nanoindents shows a decrease in shape recovery near grain boundaries and an increase in shape recovery near the new grain boundary phase, compared to grain interior. This is corroborated by analysis of nanoscale hardness and energy dissipation. Nanoscale martensitic transformation near interfaces depends largely on how the material across the interface accommodates transformation displacement. Engineering interfaces and enhancing local compatibility could drastically alter the energetics for phase transition at interfaces favorable for shape memory.

Effect of friction stir processing on microstructure of laser clad cobalt-based alloy

(The microstructural refinement of cobalt-based alloy (Stellite No. 6) by laser cladding and friction stir processing (FSP) was studied. A nanometer-sized microstructure consisting of fine carbide (particle size: 100–200 nm) and a grain (grain size: 150–250 nm) was successfully fabricated by the FSP on the laser clad cobalt-based alloy. The nanostructured cobalt-based alloy (Stellite No. 6) had an extremely high hardness of about 750 HV.

Machinability of Cobalt-based and Cobalt Chromium Molybdenum Alloys - A Review

Cobalt chrome molybdenum alloy is considered as one of the advanced materials which is widely gaining popularity in various engineering and medical applications. However, it is categorized as difficult to machine material due to its unique combination of properties which include high strength, toughness, wear resistance and low thermal conductivity. These properties tend to hinder the machinability of this alloy which results in rapid tool wear and shorter tool life. This paper presents a general review of the materials’ characteristics and properties together with their machinability assessment under various machining conditions. The trend of machining and future researches on cobalt-based and cobalt chromium molybdenum alloys are also discussed adequately.

Improvement of hardfacing process of cobalt based alloys using nanoparticles

In this paper, the application of TiO2 nanoparticles in hardfacing of hard, chemical resistant, cobaltbased alloys, is studied. The hardfacing of structural steel specimens are carried out with manual shielded metal arc welding process. The consumables were nickel chromium alloy as a buffer layer and the cobalt alloy for finishing layer. Two types of electrodes for hardfacing the control specimen were used. First was commercial, unmodified electrode, and second was the same electrode, but modified with TiO 2 nanoparticles in water solution. Infiltration of nanoparticles was carried out in three different durations of 30 seconds, 4 minutes and 8 minutes. The metallographic analysis in cross-section of the hard-faced layer, were carried out. Also, the wear resistance test was done in order to study the influence of the infiltrated nanoparticles.

Looking for New Polycrystalline MC-Reinforced Cobalt-Based Superalloys Candidate to Applications at 1200°C

For applications for which temperatures higher than 1150°C can be encountered the currently best superalloys, the γ/γ′ single crystals, cannot be used under stress because of the disappearance of their reinforcing γ′ precipitates at such temperatures which are higher than their solvus. Cobalt-based alloys strengthened by refractory and highly stable carbides may represent an alternative solution. In this work the interest was focused on MC carbides of several types. Alloys were elaborated with atomically equivalent quantities in M element (among Ti, Ta, Nb, Hf, or Zr) and in C. Script-like eutectic TiC, TaC, NbC, HfC, and ZrC carbides were successfully obtained in the interdendritic spaces. Unfortunately, only one type, HfC, demonstrated high morphological stability during about 50 hours at 1200°C. The concerned alloy, of the Co-25Cr-0.5C-7.4Hf type (in wt.%), was further characterized in flexural creep resistance and air-oxidation resistance at the same temperature. The creep behaviour was very good, notably by comparison with a more classical Co-25Cr-0.5C-7.5Ta alloy, proving that the interest of HfC is higher than the TaC one. In contrast the oxidation by air was faster and its behaviour not really chromia-forming. Significant improvements of this chemical resistance are expected before taking benefit from the mechanical superiority of this alloy.

Effect of compositional ordering on the hysteretic magnetic properties of a cobalt-based amorphous alloy

An investigation of Co69Fe3.7Cr3.8Si12.5B11 amorphous alloy shows that thermally reversible isotropic short-range compositional ordering and clustering can lead to the degradation of hysteretic magnetic properties (HMPs). At temperatures below the Curie temperature (260°С), the degradation of HMPs is caused by thermally reversible directional ordering and reduces the mobility of domain boundaries. Clusterization, a thermally irreversible process observed via small-angle X-ray scatterimg, affects HMPs only during sample annealing immediately after quenching.

Energetics of cobalt alloys and compounds and solute–vacancy binding in fcc cobalt: A first-principles database

Using extensive first-principles density functional calculations, we calculate thermodynamic properties of binary fcc cobalt-based alloys with 25 different solute elements. For each solute element X, we calculate its (a) nearest- and next-nearest-neighbor solute–vacancy binding energy, (b) dilute impurity mixing energy with respect to the equilibrium and hypothetical fcc-based reference states of the solute, (c) enthalpy of formation of cobalt-rich binary ordered compounds in the Co–X system, (d) solubility enthalpy, and other derived quantities. We find that the solute–vacancy binding energies of all the studied solutes in fcc cobalt are positive (indicating favorable binding), in contrast to nickel, aluminum, magnesium, and copper-based alloys, where mid 3d transition metal solutes have unfavorable solute–vacancy binding. We study the physical and chemical effects influencing solute–vacancy binding energy, and find that (a) it correlates broadly with solute size—larger solute atoms possess stronger binding with vacancies—and this is understood in terms of strain relief and secondary next-nearest-neighbor interactions, and (b) it follows a parabolic trend as a function of d-occupancy across the transition metal series—falling to a minimum at the middle of the series—and this is understood in terms of a d-band filling effect. We also find this d-band filling effect in other calculated quantities such as the dilute impurity volumes and dilute impurity mixing energies. To aid in building thermodynamic databases, we tabulate all the calculated thermodynamic quantities, and compare them with experimental phase diagrams data and previous literature, and find good agreement where such data is available.

Research on the oxidation behavior of novel γ/γ′-strengthened Co–9Al–10W alloys combined with chromium and rare earth elements

Abstract

Effect of heat treatment in air and a chemically active environment on the magnetic properties of cobalt-based soft magnetic amorphous alloys

The influence of heat treatment in air on the level of magnetic properties has been studied on the example of a ribbon of an amorphous cobalt-based (Co–Fe–Ni–Cr–Si–B) soft-magnetic alloy with a nearzero saturation magnetostriction. The investigation of the interaction of the ribbon surface with water and water vapor and its influence on the magnetization distribution showed the possibility of applying surface treatment to determine the sign of saturation magnetostriction. The sign of saturation magnetostriction in the initial (quenched) state confirmed the presence of a negative magnetostriction in the ribbon. Based on the results obtained, the dependence of the sign of saturation magnetostriction on the structural state that is obtained upon heat treatment has been revealed.

Wear-resistant cobalt-based coatings for injection moulds by cold spray

In this study, cold spray and high-velocity oxy fuel processes were respectively used in applying cobalt-based and nickel-based alloys on steel injection moulds. Effects of changes in the main cold spray deposition parameters and in powder composition of the cobalt-based alloy were optimised in terms of machinability and hardness improvements. A four-cavity mould was configured to allow the comparison of wear resistance between coated and heat-treated inserts in severe operating conditions. Real parts were produced by injection moulding, using a glass–fibre-reinforced polymer. Surface topography of the inserts was characterised in defined key-zones after polishing and at each scheduled stop of the moulding process. Experimental results showed that steel mould inserts coated by thermal spray and then polished can be a valid alternative to heat-treated steel for most applications.

Слабка локалізація – можлива причина особливостей температурної поведінки електроопору аморфних сплавів на основі кобальту

Слабка локалізація – можлива причина особливостей температурної поведінки електроопору аморфних сплавів на основі кобальту

Effects of Silicon Content on the Microstructure and Mechanical Properties of Cobalt-Based Tribaloy Alloys

Cobalt-based Tribaloy alloys are strengthened mainly by a hard, intermetallic Laves phase consisting of Co3Mo2Si or/and CoMoSi; therefore, silicon content plays a large role in the microstructure and performance of these materials. In this research, the microstructures of two cobalt-based Tribaloy alloys that are largely different in Si content are studied using scanning electron microscopy (SEM) with an EDAX energy dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD), fatigue strength under rotating-bending test, mechanical behavior under nanoindentation, and hardness at room and elevated temperatures using a microindentation tester. It is revealed that with higher silicon content (2.6 wt. %), T-400 has a hypereutectic microstructure with Laves phase as primary phase, whereas with lower silicon content (1.2 wt. %), T-401 has a hypoeutectic microstructure with solid solution as primary phase. T-400, containing lager volume fraction of Laves phase, exhibits better fatigue strength, in particular, at high stresses, while T-401, with less volume fraction of Laves phase, has improved ductility, exhibiting better resistance to fatigue at low stresses. The hardness of both alloys decreases with temperature, and T-401 shows higher reduction rate. T-400 is harder than T-401.

Study on friction characterization and wear-resistance properties of Si3N4 ceramic sliding against different high-temperature alloys

Ball-on-disc tests were performed to investigate the tribological behaviour of Si3N4 in contact with various high-temperature alloys, under dry sliding conditions, at different sliding speed, load and temperature. The tribological behaviour was characterized in terms of the friction coefficient and wear rate. The friction coefficient of Si3N4 sliding against high-temperature alloys was initially increased to a peak value and then decreased with the further increase of sliding speed. When Si3N4 slides against cobalt-based high-temperature alloy (GH605) the friction coefficient and wear rate was the lowest. The smallest friction coefficient was attributed to the powder like wear debris and the formation of a tribo-layer on the worn surface of Si3N4 and GH605. The primary wear mechanism of Si3N4 sliding against iron and cobalt-based high-temperature alloy was adhesion, while a combination of abrasion and adhesion were considered to be the dominant wear mechanisms in the case of sliding against nickel-based high-temperature alloy at room temperature. At high temperature, the friction coefficient and wear rate were decreased with the increase of temperature. An oxide layer was found on the worn surface of Si3N4 after sliding against high-temperature alloys and the oxidative wear was considered to be the main wear mechanism.

Characterization of fabricated cobalt-based alloy/nano bioactive glass composites

In this work, cobalt-based alloy/nano bioactive glass (NBG) composites with 10, 15 and 20wt% NBG were prepared and their bioactivity after immersion in simulated body fluid (SBF) for 1 to 4weeks was studied. Scanning electron microscopy images of two- step sintered composites revealed relatively dense microstructure. The results showed that density of composite samples decreased with increase in NBG amount. The microstructure analysis as well as energy dispersive X-ray analysis (EDX) revealed that small amount of calcium phosphate phases precipitates on the surface of composite samples after 1week immersion in SBF. After 2weeks immersion, considerable amounts of cauliflower-like shaped precipitations were seen on the surface of the composites. Based on EDX analysis, these precipitations were composed mainly from Ca, P and Si. The observed bands in the Fourier transform infrared spectroscopy of immersed composites samples for 4weeks in SBF, were characteristic bands of hydroxyapatite. Therefore it is possible to form hydroxyapatite layer on the surface of composite samples during immersion in SBF. The results indicated that prepared composites unlike cobalt-based alloy are bioactive, promising their possibility for implant applications.