Co-based Alloys Research Articles

Effect of surface roughness at elevated temperature and pressure on the oxidation behaviour of co-based alloy

Effect of surface roughness at elevated temperature and pressure on the oxidation behaviour of co-based alloy

Review of laser cladding coating on wear and fatigue of railway wheels/rails

With the rapid development of high-speed railway, wheel/rail premature wear and fatigue cracks occur frequently. Laser cladding high-quality coatings with high wear resistance and fatigue resistance on the damaged surface of wheel/rail can prolong its service life. In this review, the latest research progress of laser cladding Fe-based, Co-based and Ni-based coatings on the wear and fatigue of railway wheels/rails at home and abroad is reviewed. It is concluded that the wear resistance and fatigue resistance of Co-based alloy coatings are better than those of other alloy coatings. Adding strengthening elements to alloy powders can improve the welding process and improve the comprehensive properties of the coatings. Additionally, the laser cladding of railway wheel/rail is further envisaged as well.

The Effect of Fe on the Mechanical Properties of Stellite 6

Stellite 6 is a Co-based alloy with excellent wear and corrosion resistance, resulting in it frequently being used as a hard-facing material. The main defect that occurs in the hard-facing process is the peeling of the hard-facing layer, which is caused by thermal stress due to differences in thermal expansion coefficients. This peeling phenomenon can be prevented by using a material with an intermediate coefficient of thermal expansion as a buffer layer. Component surfaces are strengthened through a technique called hard-facing, which increases the components’ resistance to wear. In order to increase the wear and corrosion resistance of metal components, a high-hardness substance is usually coated onto their surface. Grinding is carried out to smooth the surface after the material is welded onto the base component. Small pieces, also referred to as “scrap”, are frequently produced during this surface machining procedure. In the hard-facing process, scrap containing a mixture of base material and Stellite 6 is generated during material processing. If this scrap can be used as a buffer layer, the cost of raw materials can be reduced through the recycling of resources, and the overall energy consumption for recycling can be reduced because the process of separating Stellite 6 from the scrap is eliminated. In this study, the physical properties of Stellite 6 with Fe added were explored to determine whether the scrap produced could be used as a buffer layer. When iron was added to the mixture, the amount of carbide decreased, in addition to the wear resistance and hardness decreasing. Regarding the thermal expansion coefficient, the thermal expansion coefficient of Stellite 6 was found to be 15.879 μm/m·°C at 300 °C, and that of Stellite 6 with 40% Fe added was found to be 14.313 μm /m·°C at 300 °C. The thermal expansion coefficient of carbon steel is reported to be 12.8 μm /m·°C at 300 °C; thus, Stellite 6 with 40% Fe can be used as a buffer layer for Stellite 6 and carbon steel because of its suitable thermal expansion coefficient.

Nanocrystallization Behaviour of Amorphous Co<sub>67</sub>Fe<sub>4</sub>Cr<sub>7</sub>Si<sub>8</sub>B<sub>14</sub> Alloy

The investigation addresses the structure of a Co-based alloy and its magnetic properties. The major applications of these materials are in the development of different sensors, which require materials with high permeability. The structure evolution processes need to be explored to clarify the main parameters determining the time-temperature stability. In the present paper, a nanocrystallization behavior of Co67Fe4Cr7Si8B14 amorphous alloy manufactured in the form of a ribbon was studied using X-ray diffraction and sample vibromagnetometry methods. The structure evolution induced by the 30min isothermal annealing at a temperature range of 450 - 700 °C was studied by the X-ray diffraction method, and crystallization with hcp-Co, fcc-Co, and Co2B nanophases was revealed depending on the annealing temperature. According to thermomagnetic measurements, the nanocrystallization process corresponds to a three-stage crystallization model. The crystallization onset temperature of the amorphous alloy was observed to be to equal540 °C. The Curie point and saturation magnetization of the as-quenched alloy were defined as 305 °C and 76 Am2/kg, respectively.

Grain diameter-dependent tuning of exchange anisotropy in the ion-beam sputtered Co-based full Heusler alloy coupled with antiferromagnet

We report an investigation into the substantially large and customizable exchange anisotropy (HEA) and coercivity (HC) in a set of bottom-pinned Ir7Mn93/Co2FeAl bilayer heterostructures fabricated using ion-beam sputtering at room temperature (RT) in the presence of an in-situ in-plane static magnetic field of 1 kOe. This modulation is achieved by controlling the microstructural parameter (i.e., grain diameter) of the antiferromagnetic (AF) Ir7Mn93 (IrMn) layer. These bilayers revealed strong positive exchange anisotropy (PEA) at RT, while negative exchange anisotropy (NEA) became evident when field-cooled to 15 K in the presence of 3 kOe. By systematically controlling the AF grain diameter from ∼5.39 to ∼6.94 nm, the PEA and NEA were found to increase by a factor of ∼2.1 and ∼1.8, respectively. However, once the AF grain diameter exceeded the necessary threshold for thermal stability, further enhancement in grain diameter above ∼6.94 nm led to a reduction in both HEA and HC. This decrease was attributed to a reduction in pinning centers at the AF/FM (ferromagnet) interface. The training data are fitted by utilizing various theoretical models, such as thermal relaxation, Binek's model, and spin relaxation model. The spin relaxation model was found to be applicable to fit the complete range of training data, encompassing both thermal and athermal decay, within the context of frozen and rotatable spins.

The Effect of a Coating on the Crystallization of Multicomponent Co-Based Amorphous Alloys

The effect of protective coatings on the crystallization of amorphous Co-based alloys was studied using the methods of X-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The crystallization of the amorphous alloys was studied on as-prepared samples, deformed samples, and deformed samples with a protective coating. After heat treatment, the fraction of the crystalline phase in the pre-deformed samples was higher than in the undeformed samples. When using a protective coating, the fraction of nanocrystals formed during heat treatment increased. The size of the crystals formed in deformed samples was smaller, and in the deformed samples with a protective coating, they were slightly larger than in the corresponding initial samples. The reasons for the differences in the formed structure in the amorphous alloys under study are discussed in terms of free volume.

First principles study on structural stability, mechanical, and thermodynamic properties of <i>γ'</i>-Co<sub>3</sub>(V, <i>M</i>) (<i>M</i> = Ti, Ta) phase

This research focuses on enhancing Co-based high-temperature alloys by using <i>γ'</i> precipitate phases to address the structural metastability of <i>γ'</i>-Co<sub>3</sub>(Al, W). By adding Ti and Ta, the <i>γ'</i>-Co<sub>3</sub>(V, Ti) and <i>γ'</i>-Co<sub>3</sub>(V, Ta) of Co-V alloys are stabilized, surpassing the performance of traditional Co-Al-W alloys. Utilizing a 2×2×2 supercell model and density functional theory (DFT), we investigate these alloys' phase stabilities and mechanical, thermodynamic, and electronic properties. Our findings show that <i>γ'</i>-Co<sub>3</sub>(V, Ti) phase and <i>γ'</i>-Co<sub>3</sub>(V, Ta) phases are stable at 0 K, evidenced by negative formation enthalpies and stable phonon spectra. Mechanical analysis confirms their stabilities through elastic constants and detailed evaluations of properties such as bulk modulus, shear modulus, and Young’s modulus, revealing excellent resistance to deformation and ductility. The electronic structure analysis further distinguishes <i>γ'</i>-Co<sub>3</sub>(V, Ta) for superior electronic stability, which is attributed to its lower state density and deviation from “pseudogap” peaks. Thermodynamically, the quasi-harmonic Debye model highlights the <i>γ'</i>-Co<sub>3</sub>(V, Ti) phase’s temperature-sensitive thermal expansion coefficient, while <i>γ'</i>-Co<sub>3</sub>(V, Ta) maintains higher stability at elevated temperatures. As temperature rises, both phases show decreased resistance to deformation, though they maintain comparable heat resistance due to low-temperature dependency. These results suggest that Co-V-Ti alloy and Co-V-Ta alloy can maintain their <i>γ'</i> phase stability at higher temperatures, enhancing Co-based high-temperature alloys’ performances and phase stabilities. This progress is crucial for developing new Co-based superalloys, and is of great significance for their applications and performance optimization.

Spin dependent tunneling and strain sensitivity in a Co2MnSb/HfIrSb magnetic tunneling junction: a first-principles study.

Half-metallic Co-based full Heusler alloys have captured considerable attention of researchers in the realm of spintronic applications, owing to their remarkable characteristics such as exceptionally high spin polarization at the Fermi level, ultra-low Gilbert damping, and a high Curie temperature. In this comprehensive study, employing the density functional theory, we delve into the electronic stability and ballistic spin transport properties of a magnetic tunneling junction (MTJ) comprising a Co2MnSb/HfIrSb interface. An in-depth investigation of k-dependent spin transmissions uncovers the occurrence of coherent tunneling for the Mn-Mn/Ir interface, particularly when a spacer layer beyond a certain thickness is employed. It has been found that the Co-terminated Co2MnSb/HfIrSb interface shows perpendicular magnetic anisotropy, while those with Mn-Sb and Mn-Mn termination exhibit in-plane magnetic anisotropy. Furthermore, our spin-dependent transmission calculations demonstrate that the Mn-Mn/Ir interface manifests strain-sensitive transmission properties under both compressive and tensile strain and yields a remarkable three-fold increase in majority spin transmission under tensile strain conditions. We find a tunnel magnetoresistance of ∼500% under a bi-axial strain of -3%, beyond which the tunnel resistance is found to be theoretically infinite. These compelling outcomes place the Co2MnSb/HfIrSb junction among the highly promising candidates for nanoscale spintronic devices, emphasizing the potential significance of the system in the advancement of the field.

Experimental and numerical investigations of sliding wear behaviour of an Fe-based alloy for PWR wear resistance applications

The excellent wear and corrosion resistance of Co-based alloys make them desirable for tribological applications in the nuclear industry. However, neutron activation of the Co-based alloys leads to significant occupational radiation doses. An alternative Fe-based alloy called RR2450 was developed by Rolls-Royce plc to replace these alloys. This paper presents the first comprehensive study evaluating the sliding wear resistance of RR2450 alloy in representative PWR conditions. The sliding counterface of RR2450 balls was a Co-based alloy, Haynes 25 discs. Four tests were performed at temperatures up to 80 °C, and 12 tests were performed up to 200 °C. Results showed wear performance of RR2450 balls degraded at higher loads and temperatures, with temperature having a significant role. Microstructural investigation revealed voids and hard silicide phases, negatively impacting wear resistance. Nonetheless, the wear performance of RR2450 was similar to a Co-based alloy, a=Stellite 20, at nuclear reactor conditions. Two wear tests with uneven wear tracks were selected for 3D finite element analysis. The wear simulation procedure is based on Archard’s wear equation and is implemented in a commercial FE package, ABAQUS. The FEA method was used to capture the wear on both surfaces, and was shown to predict nominal wear profiles. These comparisons with experiments show that the FEA results can provide representative wear profiles when wear depths and widths are asymmetrical and irregular.

Effects of B content on wear and corrosion resistance of laser-cladded Co-based alloy coatings

Abstract To improve the surface properties of Ti alloy, (Co34Fe8Cr29Ni8Si7)100–x B x alloy, coatings were prepared by laser cladding. The coatings—mainly composed of TiCr, Fe0.1Ti0.18V0.72, CoTi, Ti2Ni, and TiB—and amorphous phases were investigated in terms of microstructure, wear resistance, and corrosion resistance. The results showed that the microhardness of the Co-based coatings first increased and then decreased with the increase of B content. When the B content was 6%, the microhardness of the coating increased up to 1210 HV0.2 which was 3.4 times that of TC4 alloy substrate. The coatings exhibited diverse wear mechanisms that gradually transitioned from severe fatigue spalling and oxidative wear to slightly abrasive wear. The corrosion current density of Co-based coatings in 3.5 wt% NaCl solution first increased and then decreased as B contents increased. Coatings with 4% B content, however, exhibited the best corrosion resistance, which was most suitable for improving the corrosion resistance of Ti alloy.

Enhanced Anti-Corrosion Performance of Co-Cr-Mo Alloy in Molten Al by Prior Oxidation Treatment

Co-based alloys are promising alternatives to replace the currently used tool steels in aluminum die-casting molds for producing sophisticated products. Although the reaction is significantly less severe compared to that of tool steels, bare Co-29Cr-6Mo (CCM) alloy is still gradually corroded under molten Al, leading to the local failure of the alloy due to the formation of intermetallic compounds between the matrix and molten Al. This study indicated that prior oxidation treatment at 750 °C on CCM alloy is beneficial in enhancing the corrosion resistance of the alloy to molten Al. The is more pronounced in the alloy after a longer oxidation treatment. However, after oxidation for longer than 24 h, the protectiveness of the film cannot be enhanced anymore. In addition, even after the full failure of the oxide film, the thickness loss rate of a sample with prior oxidation treatment is much lower than that of a bare sample. This can be attributed to the fact that network-aligned oxide particles of the cone structure boundary inhibit both the outwards movements of alloying elements and the dissolution of the intermetallic layer.

Effect of Sn doping on low-temperature growth of Ge epilayers on half-metallic Co2FeSi

In this study, we demonstrate the low-temperature growth of a Ge layer via Sn doping in a ferromagnet/Ge/Co-based Heusler alloy multilayer on a Si(111) substrate having a vertically stacked structure. The continuous doping of 5% Sn into the Ge interlayer enables the epitaxial growth of the Ge layer on the Co-based Heusler alloy, even at ∼110 °C, and reduces the surface roughness. Elemental mapping shows that low-temperature growth via Sn doping suppresses interdiffusion at the Ge/Co-based Heusler alloy interface. The magnetic properties of the all-epitaxial CoFe/Ge/Co-based Heusler alloy structure are improved. For vertical spin-valve devices with Sn doping, the room-temperature spin signal is enhanced. These results indicate that the chemically abrupt Ge/Co-based Heusler alloy interface enhances the magnitude of the room-temperature spin signal owing to Sn-induced low-temperature growth.

Structures and electrochemical performances of La0.7Sm0.3MgNi3·6Co0.4 + xwt.%Ni (x = 0,5,10,15,20) alloys applied to Ni-MH battery

The La–Mg–Ni–Co-based AB2-type alloys, namely La0.7Sm0.3MgNi3·6Co0.4xwt.%Ni (x = 0,5,10, 15, 20), were synthesized through ball milling. The study focused on investigating the impact of Ni content on the structures and electrochemical properties. The structures of the samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Transmission electron microscope (TEM). It has been demonstrated that the experimental samples consist of a primary phase, LaMgNi4, and a secondary phase, LaNi5. The abundance of phases undergoes significant changes with variations in Ni content, while the phase composition remains constant. The results indicate that a rise in Ni concentration results in an elevation of the LaNi5 phase and a reduction of the LaMgNi4 phase. Additionally, ball milling and the addition of nickel contribute to the refinement of the alloy grains. As the nickel concentration reached 20 wt%, the cycle retention rate(S30) of the composite alloy electrode achieved its maximum value of 73.42 %. In addition, the electrochemical kinetic test findings demonstrated that the maximum D value of the hydrogen diffusion system was 1.807 × 10−10 cm2/s and that the maximum current density of the composite hydrogen storage alloy electrode was 723 mA/g when x = 0 wt%.

Forming characteristics analysis of variable-process alternated overlapping strategy based on contour description for laser melting deposition

To predict the geometric characteristics and improve the forming quality and macro-micro defects of multi-track overlapping cladding layer effectively, the experimental research of laser melting deposition single-track Co-based alloy on 42CrMo substrate was carried out. The influence trends of laser process parameters on the single-track cladding height and cladding width were analyzed, and the regression prediction models were established. A variable-process alternated overlapping strategy was proposed using the geometric functions to fit the single-track profile. The surface forming quality and macro-micro defect of different overlapping cladding layers were compared and evaluated. The results showed that the cladding height and cladding width regression models established by an improved optimization algorithm had an excellent prediction effect. The variable-process alternated overlapping cladding layer prepared by the parabolic function had a flat surface, and the fluctuation distance was 81.56 μm, which was significantly improved compared with other overlapping strategies. The surface flatness of the continuous overlapping cladding layer was the worst and the spheroidization defect was the most unsatisfied. The internal defects of the constant-process alternated overlapping cladding layer were the most terrible, with more non-fusion and cracks caused by oxides. The variable-process alternated overlapping strategy proposed in this study can effectively prepare a multi-track cladding layer with a smooth surface and dense interior, which provides essential theoretical guidance for the near-net forming of component surface deposition and repair.

Differences in Oxidation Behavior of Conventionally Cast and Additively Manufactured Co-Base Alloy MAR-M-509

AbstractHigh-temperature oxidation behavior of conventionally cast and additively manufactured (AM) Co-base alloy MAR-M-509 was compared in the present study. The specimens were exposed in air at 1000 °C and characterized by means of scanning electron microscopy equipped with energy/wavelength dispersive x-ray spectroscopy (EDX/WDX) and electron backscatter diffraction as well as transmission electron microscopy. Substantial differences in the oxidation processes of two alloy versions were observed. Faster oxidation of the cast alloy was mainly induced by (1) oxidation of coarse primary carbides, (2) internal oxidation and nitridation processes and (3) incorporation of other alloy constituents (e.g., Co, Ni, W) into the Cr-oxide scale. AM specimens, in contrast, formed a more homogeneous, thinner and better adherent external oxide scale. The results are discussed in terms of differences in the chemical composition and alloy microstructure, including the grain size distribution in the material and the morphology of the strengthening precipitate phases.

Clinical and laboratory study of corrosion resistance of a base dental alloy for selective laser melting.

CAD/CAM technologies are becoming widely used for the production of metal ceramic dental restorations. Powder Co-based alloys are developed for selective laser melting. The corrosion resistance of the dental alloy affects the biocompatibility, functional suitability, and longevity of the prosthetic restoration.

Effect of Y2O3 on the Microstructures and Properties of Magnetic Field-Assisted Laser-Clad Co-Based Alloys

Effect of Y2O3 on the Microstructures and Properties of Magnetic Field-Assisted Laser-Clad Co-Based Alloys

High-throughput design of Co-based magnetic Heusler compounds

High-throughput (HTP) density functional theory (DFT) calculations are carried out on Co-based Heusler alloys, i.e., Co2YZ and X2CoZ (where X, Y, and Z range from lithium (Li) to bismuth (Bi) excluding inert gas and 4f rare-earth elements) in both cubic and tetragonal structures of the regular and inverse Heusler phases. After evaluating the thermodynamic stabilities based on the formation energy (ΔEf) and the distance to the convex hull (ΔEHD), we validate the HTP calculations with 65 experimentally known cases and further predict 158 novel compounds with ΔEHD smaller than 50 meV/atom, in which 117 compounds exhibit finite magnetization larger than 1 μB/f.u.. The novel Co-based Heuslers predicted by our HTP work also includes some all-d-metal compounds. In contrast to the conventional Heuslers with dominating pd hybridization, the all-d-metal Heuslers consisting of mainly dd hybridization cannot be properly interpreted by Burch’s rule. The Slater–Pauling rule, on the other hand, is found to well describe the relationship between the intrinsic magnetic properties, including the total spin moment and Curie temperature, and the number of valence electrons. Furthermore, magneto-crystalline anisotropy is calculated for stable tetragonal compounds, providing useful information for potential applications in the fields of permanent magnets and magnetic recording materials.

A study of crystallization behavior and magnetic property of Co-based alloy

The crystallization behavior and magnetic properties of Co-based alloy are investigated by DSC, XRD, TEM, VSM, and impedance analyzer. The results indicate that the non-isothermal crystallization of Co50Fe25Nb15B10 alloy has a significant glass transition with a supercooled liquid region of about 80 K. When the heat treatment is above crystallization temperature, some phases appear successively as the Co2B and (Co, Fe)21Nb2B6, and with the increase of annealing temperature, the values of coercivity Hc and saturation magnetic induction strength Bs increase correspondingly. After measuring the impedance effect of the Co-based alloy, it is found that the increase in impedance value is attributed to the decrease in magnetic anisotropy performance of the alloy, and the impedance curves of both amorphous and nanocrystalline alloys show a similar single peak trend. However, the crystallization phases after annealing form with a large size that hind the magnetization process resulting in a significant decrease of (ΔZ/Z)max value.

Effect of heat treatment on the microstructure and mechanical properties of a dual phase Al14Co41Cr15Fe10Ni20 high entropy alloy

The microstructure and mechanical properties of Al14Co41Cr15Fe10Ni20 high entropy alloy is investigated in this work. Both the as-cast and homogenized (1200 °C/20 h) alloys show a dual phase microstructure consisting from a dendritic solid solution FCC phase and an interdendritic B2 (BCC) phase. Aging treatments in the temperature range of 750 °C–1000 °C were applied on samples for 20 h. Uniform distribution of precipitates in both dendritic and interdendritic regions were observed after performing the aging treatments. It is observed that with increasing the aging temperature from 750 °C to 1000 °C, the size of precipitates increases and the hardness of alloys decreases due to over-aging. The aged alloy with optimized hardness was selected for further room temperature and high temperature tensile tests. The results of mechanical tests indicate that the room temperature mechanical properties of the investigated alloy are comparable to the mechanical properties of commercial Co-based alloys, although the high temperature ductility of the alloy is very poor in comparison with commercial alloys. The obtained results in this work could be used for the further development of high entropy alloys with dual phase FCC/B2 microstructures.