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In this study, crystalline Co2B powder production was carried out by a one-step carbothermal reduction method starting from cheap, easily accessible oxide-based materials. Firstly, to determine the carbothermic CoxB formation conditions, the decomposition temperatures of the raw materials were analysed by TG/DTA, and the temperature-varying Gibbs free energies of the expected reactions were calculated. Then, Co2B production was carried out at constant CoO/B2O3/C (3.22/1.5/1.3) weight ratios at temperature (1273-1473 K) and time (30-270 min). Scanning electron microscopy (SEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) were used to characterize the particles. XRD results showed that reaction temperature and time are the primary control on CoxB formation and singlephase crystalline Co2B particles with crystallite sizes of 88 nm were successfully produced at 1473 K and 150 min. The permanent magnetization, saturation magnetization, and coercivity values of Co2B particles were defined as 16.58 Oe, 35.361 emu/g, 0.501 emu/g, respectively. [ABSTRACT FROM AUTHOR]

The solidification evolution of an ASTM F75 alloy was studied for samples quenched during directional cooling. These samples were obtained using five extraction rates (1.2–18 mm/min) and two temperature gradients (6 and 12 K/mm), leading to a 25-fold change in the cooling rate (0.13–3.31 K/s). The solidification range for this alloy is observed to be approximately 200 °C. The solid grows more rapidly in the first 100 °C of this interval, where a solid fraction of approximately 0.8–0.9 is reached. Coarsening of the Secondary Dendrite Arm Spacing, SDAS, occurs mainly during this growth period. This behavior defines an effective temperature interval for the SDAS coarsening instead of the whole solidification interval. Consideration of this effective temperature interval enables us to reconcile the measured SDAS-cooling rate relationship with that obtained from the data for the cast samples. A model of the SDAS coarsening during anisothermal solidification of multicomponent alloys is proposed. The predictions of this model compare well with the present experimental results.

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. [ABSTRACT FROM AUTHOR]

The paper studies the influence of manganese ion implantation on the cavitation erosion behaviour of the HIPed Stellite 6. The implantation process was conducted using implantation energy 175 keV, and the fluences of implanted ions were set at 5×1016 Mn+/cm² and 1×1017 Mn+/cm². The microstructure of the samples was investigated using scanning electron microscopy and X-ray diffraction. The cavitation erosion tests were carried out according to the ASTM G32 standard with the stationary specimens configuration. The cavitation erosion-damaged surfaces of unimplanted and implanted samples were qualitatively investigated using scanning electron microscopy. Moreover, the phase development due to the ion implantation and cavitation erosion was analysed using the X-ray diffraction technique. The HIPed Stellite 6 microstructure is based on the cobalt-containing matrix consisting of γ (face-centred cubic) and" (hexagonal close-packed) crystal structures and Cr7C3 chromium carbides. Generally, the applied implantation parameters have a minimal effect on the microstructure and erosion resistance. The X-ray diffraction analysis shows a negligible effect of implantation on the microstructure. The implantation using 1 × 1017 Mn+/cm2 seems the most promising for prolonging the cavitation erosion incubation stage as well as for minimalizing the material loss (30.4 mg) and erosion rate (1.8 mg/h); the unimplanted Stellite 6 shows these indicators at the comparable level of 34.5 mg and 2.0 mg/h, respectively. The study confirmed that cavitation loads induce the face-centred cubic to hexagonal close-packed phase transformation in the cobalt-based matrix. The cavitation erosion mechanism relies on the material loss initiated at the carbides/matrix interfaces. Deterioration starts with the cobalt matrix plastic deformation, weakening the restraint of Cr7C3 carbides in the metallic matrix. First, the deformed cobalt matrix and then hard carbides are removed at the interfaces. Further, the cobaltbased matrix undergoes cracking, accelerating material removal, pits formation, and craters growth. [ABSTRACT FROM AUTHOR]

This Part 3 focuses on the detailed study of the nanostructures forming in amorphous microwires which were previously received and described in the Part 2. The clustering process was studied at long-term DC Joule heating's much lower the crystallization temperature. Particular attention is paid to the study of the redistribution of the components of the initial stage of crystallization. The studies were carried out using the Atom Probe Tomography method (APT), which allows for the identification of individually considered atoms. A description and analysis of APT data processing techniques are provided for studying the cluster structure and distribution of elements in the amorphous matrix and crystalline phases. To identify crystalline phases, data obtained using High-Resolution Transmission Electron Microscopy (HR-TEM) and Scanning Transmission Electron Microscopy (STEM), as well as X-Ray Powder Diffraction (XRPD) with synchrotron radiation source were used. The applied techniques made it possible to establish that the formation of nuclei of crystalline phases is preceded by three stages of the amorphous microwire matrix evolution. At the first stage, clusters of the first and second coordination spheres appear. At the second stage, the clusters coagulate and become more than 2 nm in diameter, the stage ends with the predominance of Co-rich and silicide Me-Si clusters. At the third stage, they grow to an average diameter of 4.5 nm, the predominance of clusters of this type remains, and the formation of nuclei of crystalline phases α-Co and Co 2 Si, with a size of about 8 nm, occurs. This stage is characterized by high stable soft magnetic properties. With a further increase in the heat treatment temperature, a gradual deterioration of the soft magnetic properties and further structural transformation occur – structures of joint crystalline phases from two crystalline phases α-Co and Co 2 Si are formed in the amorphous matrix, and crystallization occurs with the alternation of these two phases. This leads to a significant redistribution of alloy components. As a result, an amorphous barrier layer is formed in the amorphous matrix near the surface of the growing two-phase substructures, enriched in chromium and silicon; this layer affects the growth of crystalline phases, slowing it down. • The effect of the DC Joule heating on the amorphous state evolution is shown. • Clusters and nuclei of crystalline phases using Atom Probe Tomography method were investigated. • The formation of nuclei of crystalline phases is preceded by three stages of the amorphous microwire matrix evolution. • The influence of chromium on the processes of clustering and the formation of crystalline phases is shown. • At the initial stage of crystallization in the amorphous matrix the formation of crystalline two-phase substructures is observed. [ABSTRACT FROM AUTHOR]

• Results of experimental determination of fatigue life of S960 steel with surface layers are presented. • Laser cladded functional layers are aluminium bronze, hardchrome, cobalt alloy and stainless steel. • The fatigue life is characterized by S-N curves determined on specimens subjected to three-point bending. • The residual life is discussed in relation to the influence of the HAZ of the base material and defects of microstructure at the interface of the HAZ and laser cladded layers. This study evaluates the fatigue life of S960 high-strength steel with laser-cladded layers of aluminium bronze, hard chrome, cobalt alloy, and stainless steel, using three-point bending tests. Our results demonstrate that while these cladded layers offer potential for enhanced surface properties, they generally reduce the material's fatigue life due to alterations in the heat-affected zone and the introduction of microstructural defects at layer interfaces. The extent of fatigue life reduction varies with the type of cladded layer, highlighting the importance of optimizing laser cladding parameters to minimize detrimental effects and improve component longevity. [ABSTRACT FROM AUTHOR]

The combustion of highly exothermic multicomponent mixtures of Co3O4/Cr2O3/Nb2O5/Al with additives of MoO3, WO3, and carbon (graphite) under overload up to 200 has been studied. It has been shown that the introduction of carbon into the initial mixture has a marked effect on the combustion, formation of chemical composition, and structure of combustion products. When the weight percentage of carbon in the initial mixture increases from 0 to 3.9%, the burning rate decreases by more than half and the rate of dispersion of combustion products and the mass loss increase markedly. Under the action of overload, the two-phase melt of combustion products is stratified into two layers, which crystallize upon cooling. The lower metal layer contains Co, Nb, Cr, W, Mo, C, and impurity aluminum, and the upper layer contains mainly Al2O3. With an increase in the carbon content above 4.0%, the separation of the metal and oxide phases ceases, and with a further increase, the flammability limit is reached. With an increase in the carbon content in the mixture from 0 to 3.9%, its concentration in the cast composite material reaches 5.4%, the Al content is about 4.0% and the content of Co, Nb, Cr, W, and Mo changes slightly. The combustion slag contains reducing metal oxide (Al2O3) and impurity Cr2O3 dissolved in it. [ABSTRACT FROM AUTHOR]

The effect of the conditions and temperature of static tensile deformation on the mechanical properties and structure of a high-temperature KKh28M6 cobalt alloy (Co–Cr–Mo system) prepared by selective laser melting is studied. An effect of the loading conditions at temperatures of 900–1100°C on the ultimate tensile strength of the alloy is revealed. [ABSTRACT FROM AUTHOR]

Two alloys were used in order to extend the service life of marine engine exhaust valve head. Layers of cobalt base alloys were made of the powders with with chemical composition as follow: the layer marked L12; C-1,55%; Si-1,21%; Cr-29,7%; W-9%; Ni-2%; Mo

Implants are widely used in orthopedic surgery and are gaining attention of late. However, their use is restricted by implant-associated infections (IAI), which represent one of the most serious and dangerous complications of implant surgeries. Various strategies have been developed to prevent and treat IAI, among which the closest to clinical translation is designing metal materials with antibacterial functions by alloying methods based on existing materials, including titanium, cobalt, tantalum, and biodegradable metals. This review first discusses the complex interaction between bacteria, host cells, and materials in IAI and the mechanisms underlying the antibacterial effects of biomedical metals and alloys. Then, their applications for the prevention and treatment of IAI are highlighted. Finally, new insights into their clinical translation are provided. This review also provides suggestions for further development of antibacterial metals and alloys. [ABSTRACT FROM AUTHOR]

Implants are widely used in orthopedic surgery and are gaining attention of late. However, their use is restricted by implant-associated infections (IAI), which represent one of the most serious and dangerous complications of implant surgeries. Various strategies have been developed to prevent and treat IAI, among which the closest to clinical translation is designing metal materials with antibacterial functions by alloying methods based on existing materials, including titanium, cobalt, tantalum, and biodegradable metals. This review first discusses the complex interaction between bacteria, host cells, and materials in IAI and the mechanisms underlying the antibacterial effects of biomedical metals and alloys. Then, their applications for the prevention and treatment of IAI are highlighted. Finally, new insights into their clinical translation are provided. This review also provides suggestions for further development of antibacterial metals and alloys.

Nowadays, high-precision machines require lightweight materials with very high strength. Ion implantation is used to improve the mechanical strength of the material. A further paper presents the influence of manganese and nitrogen ion implantation on changes of microhardness of the surface layer of cobalt alloy. Samples were analyzed with the SEM-EDS Phenom ProX microscope. Microhardness was assessed with the Vickers method, and the loads of 1 gf (0.00981 N) and 5 gf (0.049 N) was applied using a FM-800 from Future-Tech microhardness meter. At a load of 1 gf, the penetration depth of the implanted specimens was reached not exceeding 0.5 um. At this depth, all samples showed an increase in microhardness compared to the unimplanted sample. The highest increase in microhardness was achieved after implantation of Mn ions with dose D=1∙1017 Mn+/cm2 and energy E=175 keV. The increased load on the indenter to 5 gf reduced the microhardness differences between implanted and unimplanted samples.

The article describes the method of obtaining a special medical alloy based on Co-Cr, which is also used to create implants for large joints of a man (hip and knee). The analysis of the optimal relationship between the alloy components is carried out. Also in this article the results of investigations of technological plasticity, microstructure, phase composition of samples from alloy are presented. Co-Cr analysis, subjected to longitudinal draft and extrusion.

The paper presents the effect of ZrO2 layer deposition by the ALD process on the physicochemical properties of cobalt-based alloys (Realloy C and EOS CoCr SP2) intended for application in prosthetic dentistry. The paper shows the results of the surface roughness measurements made by the AFM method as well as the wettability and free surface energy measurements. Additionally,potentiodynamic tests of pitting corrosion resistance and electrochemical impedance spectroscopy in a solution of artificial saliva were carried out. Tests were carried out on the samples in the initial state and after surface modification with the ZrO2 layer. Based on these results, the usefulness (e.g. enhancement of corrosion resistance and biocompatibility) of the proposed ZrO2 layer on the cobalt alloys was assessed.

Metallic biomaterials are considered safe materials for the fabrication of orthopedic prostheses due to their mechanical stability. Among this group, cobalt-chromium-molybdenum alloys are commonly used. Nevertheless, adverse reactions on tissues caused by the liberation of metallic ions are a limitation. Therefore, the modification of biometallic material surfaces has become a topic of interest, especially the improvement of the wear resistance to retard the degradation of the surface. In this work, dimples obtained at different processing parameters by an ns-pulse laser were texturized on an ASTM F-1537 cobalt alloy. Surfaces were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy, and Raman spectroscopy. The mechanical integrity of the surface was evaluated using a 3D surface analyzer and Vickers indentation tests. The tribological response was studied employing a ball-on-disc tribometer under lubricated conditions tracking the coefficient of friction, volume loss, wear rate, and surface damage by SEM. The variation of the laser power, repetition rate, and process repetitions slightly modified the chemistry of the surface (oxides formation). In addition, the rugosity of the zone treated by the laser increased. The texturized samples decreased the wear rate of the surface in comparison with the untreated samples, which was related to the variation of the dimple diameter and dimple depth.

Two alloys were used in order to extend the service life of marine engine exhaust valve head. Layers of cobalt base alloys were made of the powders with chemical composition as follow: the layer marked L12; C-1.55%; Si-1.21%; Cr-29.7%; W-9%; Ni-2%; Mo<0.01%; Fe-1.7%; Co-54.83% and the layer marked N; C-1.45%; Co-38.9%; Cr-24.13%; Ni-10.43%; W-8.75%; Fe-7.64%; Mo-7.56%; Si-2.59%. Base metal was valve steel after heat treatment. It was consisted of: C-0,374%; Cr-9,34%; Mn-0.402%; Ni-0.344%; Si-2.46%; Mo-0.822%; P-0.0162%; S-0.001%. Layers on the valve faces were produced by laser cladding using the HPDL ROFIN DL020 laser. Grinding treatment is a very popular form of regeneration of seat and valve plug adhesions. Properly performed grinding operation ensures dimensional and shape accuracy of the surface from 7 to 5 accuracy class and surface roughness Ra not less than 0.16 µm, depending on the object and method of grinding. The 75H and 150S types are a significantly simplified form of valve plug face grinders. Finishing treatment was carried out with a Chris-Marine AB75H sander on a sanding stand equipped with a compressed air system - the stand was designed by the author. The sander has been set up to the surface of the valve stem so that the grinding angle of the valve faces is 30°+10°. A flat grinding wheel T1CRA54--K was used for machining. The plunge feed was 0.01 mm/rev. The thickness of the welded layer after grinding was 1.2 mm. Both valves were installed in the ship's engine and were used in real life. After 2000 hours of operation, the valve marked N was damaged. The valve marked L12 showed no damage and was in operation for the next 1000 hours. [ABSTRACT FROM AUTHOR]

From the wide range of engineering materials traditional Stellite 6 (cobalt alloy) exhibits excellent resistance to cavitation erosion (CE). Nonetheless, the influence of ion implantation of cobalt alloys on the CE behaviour has not been completely clarified by the literature. Thus, this work investigates the effect of nitrogen ion implantation (NII) of HIPed Stellite 6 on the improvement of resistance to CE. Finally, the cobalt-rich matrix phase transformations due to both NII and cavitation load were studied. The CE resistance of stellites ion-implanted by 120 keV N+ ions two fluences: 5 × 1016 cm−2 and 1 × 1017 cm−2 were comparatively analysed with the unimplanted stellite and AISI 304 stainless steel. CE tests were conducted according to ASTM G32 with stationary specimen method. Erosion rate curves and mean depth of erosion confirm that the nitrogen-implanted HIPed Stellite 6 two times exceeds the resistance to CE than unimplanted stellite, and has almost ten times higher CE reference than stainless steel. The X-ray diffraction (XRD) confirms that NII of HIPed Stellite 6 favours transformation of the ε(hcp) to γ(fcc) structure. Unimplanted stellite ε-rich matrix is less prone to plastic deformation than γ and consequently, increase of γ phase effectively holds carbides in cobalt matrix and prevents Cr7C3 debonding. This phenomenon elongates three times the CE incubation stage, slows erosion rate and mitigates the material loss. Metastable γ structure formed by ion implantation consumes the cavitation load for work-hardening and γ → ε martensitic transformation. In further CE stages, phases transform as for unimplanted alloy namely, the cavitation-inducted recovery process, removal of strain, dislocations resulting in increase of γ phase. The CE mechanism was investigated using a surface profilometer, atomic force microscopy, SEM-EDS and XRD. HIPed Stellite 6 wear behaviour relies on the plastic deformation of cobalt matrix, starting at Cr7C3/matrix interfaces. Once the Cr7C3 particles lose from the matrix restrain, they debond from matrix and are removed from the material. Carbides detachment creates cavitation pits which initiate cracks propagation through cobalt matrix, that leads to loss of matrix phase and as a result the CE proceeds with a detachment of massive chunk of materials.

The main purpose of the research was to analyze the influence of surface modification of the cobalt-based alloy used in dental prosthetics by applying zirconium oxide (ZrO2) layers using the ALD (Atomic Layer Deposition) method. The samples were made using the DMLS (Direct Metal Laser Sintering) technique, and their surfaces were prepared in accordance with the principles of removable partial dentures (RPDs). A 50 nm-thick zirconium oxide coating was applied to the prepared substrates. This paper deals with the issues of prosthetic stomatopathy, which is a complex of pathological changes occurring in approx. 40% of the Polish population using removable dentures. Often, these changes, occurring on the mucosa, are related to improper performance, allergic reactions or the multiplication of bacteria on the surface of partial dentures. An innovative method of surface modification was proposed, together with the analysis of its influence on the physicochemical properties of the alloy and the adhesion of bacteria to the surface.

Nickel is often added to cobalt-based superalloys to stabilize their austenitic structure. In this work the effects of Ni on several high temperature properties of a chromium-rich cobalt-based alloy reinforced by high fraction of TaC carbides are investigated. Different thermal analysis techniques are used: differential scanning calorimetry (DSC), thermo-mechanical analysis (TMA) and thermogravimetry (TG). Results show that the progressive addition of nickel did not induce great modifications of microstructure, refractoriness or thermal expansion. However, minor beneficial effects were noted, including reduction of the melting temperature range and slight decrease in thermal expansion coefficient. The most important improvement induced by Ni addition concerns the hot oxidation behavior. In this way, introducing several tens wt % Ni in this type of cobalt-based alloy may be recommended.

Nowadays, high-precision machines require lightweight materials with very high strength. Ion implantation is used to improve the mechanical strength of the material. A further paper presents the influence of manganese and nitrogen ion implantation on changes of microhardness of the surface layer of cobalt alloy. Samples were analyzed with the SEM-EDS Phenom ProX microscope. Microhardness was assessed with the Vickers method, and the loads of 1 gf (0.00981 N) and 5 gf (0.049 N) was applied using a FM-800 from Future-Tech microhardness meter. At a load of 1 gf, the penetration depth of the implanted specimens was reached not exceeding 0.5 um. At this depth, all samples showed an increase in microhardness compared to the unimplanted sample. The highest increase in microhardness was achieved after implantation of Mn ions with dose D=1⋅1017 Mn+/cm² and energy E=175 keV. The increased load on the indenter to 5 gf reduced the microhardness differences between implanted and unimplanted samples. [ABSTRACT FROM AUTHOR]

Cobalt alloys are used when improved cavitation-erosion (CE) resistance is needed. Low temperature plasma nitriding - (LTPN) is known to greatly enhance the CE resistance of austenitic and duplex stainless steels, due to formation of a very hard, super-saturated fcc - phase, known as expanded austenite or S-phase. In this work, Low Temperature Plasma Nitriding of a non-standard Co-Cr alloy was carried out to explore the formation of an expanded S-phase hard layer and to assess its effect on the CE resistance of the Co-Cr alloy. The Co-Cr samples, containing α-fcc and ε-hcp solid solutions phases, were plasma nitrided at 350 °C and 400 °C for 20 h. The CE tests were carried out in a vibratory cavitation equipment according to ASTM G32-92. Microstructural and micromechanical characterization of the specimens indicated the formation of an expanded S-phase fcc layer, containing small amounts of CrN. Plasma nitriding at 400 °C and greater amounts of α-fcc volume fraction in the matrix led to thicker and harder (10.5 GPa) S-phase layers. The 400 °C nitrided samples exhibited higher CE resistances than the non-nitrided samples, with up to 267% greater incubation times and 5 times reduced wear rate. All Co30Cr19Fe samples showed higher CE resistances than AISI 304 and only the solution-treated sample showed lower CE resistance than Stellite 6. The results are discussed in terms of the mechanisms of material removal, during the initial stages of CE, which are controlled by plastic deformation, with formation of slip steps, grain boundaries protrusion and material removal from these protruded areas. Twin boundaries are preferably eroded. The increase in nitrogen content increases the elastic energy returned to the environment and decreases the amount of plastic energy absorbed by the alloy, at cavitation impact spots. • Cavitation erosion resistance of low temperature plasma nitrided Co30Cr19Fe alloy was determined; • Low temperature plasma nitriding greatly improved wear resistance and mechanisms; • A expanded and distorted austenite layer, known as S-phase, was formed for all conditions; • Plasma-treated Co30Cr19Fe samples exhibited higher cavitation erosion resistance than Stellite 06 and AISI 304. [ABSTRACT FROM AUTHOR]

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The material subject to investigation was two commercial alloys of cobalt CoCrW (No. 27 and 28) used in prosthodontics. The scope of research included performing an analysis of microstructure and functional properties (microhardness, wear resistance and corrosion resistance), as well as dilatometric tests. The examined alloys were characterized by diverse properties, which was considerably influenced by the morphology of precipitates in these materials. Alloy No. 27 has a higher corrosion resistance, whereas alloy No. 28 shows higher microhardness, better wear resistance and higher coefficient of linear expansion. Lower value of the expansion coefficient indicates less probability of initiation of a crack in the facing ceramic material.

Wear resistant alloys are required for deployment in pressurised water reactor primary circuits and in this context, the corrosion behaviour of a cast cobalt-based alloy following exposure for 30 days in lithiated water at 300 °C was investigated. Corrosion of the surface was observed, resulting in the formation of a ∼100 nm thick chromium- and silicon-rich oxide. Preferential corrosion of the matrix at its interface with just one of the carbide types was observed to a depth of ∼1 μm; for the first time this was shown to be not due to any inhomogeneity in the matrix but instead to be an electrochemical effect. [ABSTRACT FROM AUTHOR]

The paper presents the effect of ZrO2 layer deposition by the ALD process on the physicochemical properties of cobalt-based alloys (Realloy C and EOS CoCr SP2) intended for application in prosthetic dentistry. The paper shows the results of the surface roughness measurements made by the AFM method as well as the wettability and free surface energy measurements. Additionally, potentiodynamic tests of pitting corrosion resistance and electrochemical impedance spectroscopy in a solution of artificial saliva were carried out. Tests were carried out on the samples in the initial state and after surface modification with the ZrO2 layer. Based on these results, the usefulness (e.g. enhancement of corrosion resistance and biocompatibility) of the proposed ZrO2 layer on the cobalt alloys was assessed. [ABSTRACT FROM AUTHOR]

The results of qualitative and quantitative changes in phase composition as well as microstructure changes of amorphous Co 69 Fe 4 Cr 4 Si 12 B 11 microwires at three stage crystallization process of are presented. After first and second stages the amount of crystalline Co-phase was 36 wt%. To study magnetization of the alloy during heating, exposure and cooling a unique vibration magnetometer with a chemical microreactor was used. The unique vibration magnetometer was used for low inertia real-time measurements under controlled atmosphere. The Curie temperatures of phases formed in the crystallization process were determined. Based on the analysis of magnetization kinetic curves, nucleation and growth mechanisms were established on the stage of primary crystallization. It was found that a one-dimensional mechanism is responsible for the growth of Co-based crystals and leads to the formation of a specific needle-shaped structure. At the second crystallization stage of a metastable phase with a Co 23 B 6 structure type was formed. The Curie temperature of this phase was 165 °C. [ABSTRACT FROM AUTHOR]

The first principle molecular dynamics simulations based on the density functional theory were performed to study the local structure of Co B-based glassy alloys. It was evidenced that the B-centered non-distorted (regular) Kasper polyhedra with a coordination number (CN) of 9–10, i.e. <0, 3, 6, 0> and <0, 2, 8, 0>, are primary structure-forming clusters in Co B-based glassy alloys. The formation of these regular clusters can be attributed to the efficient dense packing as well as the strong chemical interaction indicated by the results of chemical short range order parameter and electronic charge density. Compared with the Co 65 B 35 glassy alloy, the Ta-bearing Co 57 B 35 Ta 8 alloy has a higher fraction of Z9 and Z10 (Z = CN) Kasper polyhedra. A higher fraction of these regular Kasper polyhedra and their efficient and stable packing over medium range are likely to constitute the relatively stable regions which may compete with the corresponding crystals, and thus reduce atomic diffusivity and increase the viscosity of liquid/glassy structures. This result is in favor of higher thermal stability and better resistance to plastic flow. Therefore, the Co 57 B 35 Ta 8 glassy alloy possesses a larger glass-forming ability and a higher mechanical strength than the Ta-free glassy alloy. [ABSTRACT FROM AUTHOR]

The influence of nitrogen ion implantation on the tribological properties of Stellite 6 cobalt alloy was investigated. The tribological tests were conducted using a pin / ball on disc in the atmosphere of engine fuels. In the study, cobalt alloy was implanted with 60 keV nitrogen ions at the fluence of 1·1016 and 5·1016 N+/cm2. The wear trace was measured using the Form Talysurf Intra Taylor Hobson profilometer. The results demonstrate that nitrogen ion implantation affects the friction coefficient and wear. The effect of nitrogen ion implantation depends on the environment in which the tribological test is carried out, the sample temperature and the presence of friction products in the friction node. [ABSTRACT FROM AUTHOR]

The series of amorphous ferromagnetic glass-coated microwires of composition Co69Fe4Cr4Si12B11, manufactured by Taylor-Ulitovsky technique, was investigated. The series consisted of six types microwires fabricated under different technological conditions. The metallic nucleus and glass coating diameters of microwires ranged within 11-20 µm and 26-35 µm, respectively. Investigation of the magnetic properties of microwires was carried out using induction and the small-angle magnetization rotation techniques. The anisotropy field, the magnetostriction constant and the average value of the quenching stresses are estimated for all types of microwires. Based on the experimental data obtained, influence of technological parameters on the microwire's magnetic properties was investigated. [ABSTRACT FROM AUTHOR]

Cerebral aneurysm clip blades crossing during surgery is well known as scissoring. Scissoring might cause rupture of the aneurysm due to laceration of its neck. Although aneurysm clip scissoring is well known, there have been few reports describing the details of this phenomenon. Quasi-scissoring phenomenon was introduced mechanically by rotating the clip head attached to a silicone sheet. The anti-scissoring torque during the twist of the blades was measured by changing the depth and the opening width. The closing force was also evaluated. Sugita straight clips of titanium alloy and cobalt alloy were used in the present study. In both materials, the anti-scissoring torque and the closing force were bigger 3 mm in thickness than 1 mm. The initial closing forces and the anti-scissoring torque values at each rotation angles were increased in proportion to depth. Closing forces of titanium alloy clip were slightly higher than those of cobalt alloy clip. By contrast, anti-scissoring torque values of cobalt alloy clip were bigger than those of titanium alloy clip in all conditions. In condition of 3 mm in thickness and 3 mm in depth, anti-scissoring torque vales of titanium alloy clip decreased suddenly when an angle surpassed 70 degrees. Aneurysm clip scissoring phenomenon tends to occur when clipping the aneurysm neck only with blade tips. Based on the results of this experiment, titanium alloy clip is more prone to scissoring than cobalt alloy clip under the condition that the wide blade separation distance and the shallow blade length. Graphical abstract: [ABSTRACT FROM AUTHOR]

The development of porous hydroxyapatite (HA) and composite TiO 2 /HA coatings on metallic biomaterials has received a great deal of attention during recent years. This is due to their superior properties in biomedical applications, including the better biointegration and mechanical stability of implants in the bone. Their poor adhesion strength to metallic substrates often makes them unsuitable for use in medicine, therefore the present work has focused on the electrophoretic deposition of the porous HA and nanocrystalline nc-TiO 2 /HA coatings which adhere well to the metallic substrate, as well as investigation of their influence on the Co-28Cr-5Mo alloy’s electrochemical corrosion resistance in Ringer’s solution. The mixture of nanometric and submicron size HA and nanometric TiO 2 powders were used to electrophoretically deposit porous coatings on a cobalt alloy. The microstructure of the coating and substrate has been examined by scanning- and transmission electron microscopy and X-ray diffractometry. Both types of coatings, 6 μm thick, were highly porous with an open pore diameter up to 1 μm. The HA coatings were composed of nanocrystalline nc-HA particles uniformly distributed within submicrocrystalline sm-HA particles. In the nc-TiO 2 /HA coating, three types of particles occurred, namely nc-HA, nc-TiO 2 and sm-HA. The HA coating was free of microcracks and voids, while “dried mud” microcracks occurred in the nanocomposite nc-TiO 2 /HA coating due to a mismatch in the coefficient of thermal expansion for both coating components. The transformation of anatase-to-rutile was observed after sintering of the nc-TiO 2 /HA coatings. The adhesion of the coatings to the underlying substrate material was investigated by the micro-scratch technique. The results show that EPD is convenient for deposition of well-adhered porous HA and nc-TiO 2 /HA coatings on a cobalt alloy. However, due to a homogeneous morphology free of microcracks, the HA coating exhibited much better adhesion to the substrate material than that of the nc-TiO 2 /HA coating. The application of both types of coating improved the corrosion resistance of the cobalt alloy in Ringer’s solution. The corrosion resistance of the HA coated alloy free of microcracks was higher than that of the nc-TiO 2 /HA coated one. The results of this work confirm EPD as a convenient method to develop porous coatings on cobalt alloys with potential medical application. [ABSTRACT FROM AUTHOR]

The problem of creation of small size wideband sensitive sensors of magnetic field with a narrow directional diagram and a small coefficient of thermal drift is actual and requires searching for new magnetic materials. We present the results of the development of the flux-gate sensors with the 20 μm magnetic core of amorphous foils of ММ-3Со and ММ-5Со cobalt alloys and magnetoelectric transducers with magnetic field sensitive element of NiMnGa martensite single-crystal. The peculiarities of our sensors are the usage of the parametric amplification and related to it the strong nonlinearity of the dependences of magnetic permeability of amorphous foil and NiMnGa single-crystal magnetostriction on the magnetic field amplitude. [ABSTRACT FROM AUTHOR]

A silicate ceramic and a Co-based superalloy are put in contact at 700 °C and are submitted to fretting wear (small amplitude reciprocating movements). The present interface is a plane to plane 4 mm contact that is studied in cross section through SEM-EDX, high resolution TEM and XPS. The tribological test results in the formation of thick (20 μm), compact third body that adheres on both counterparts in the interface. This third body, which is formed from mixed, grinded and sintered debris reacting with surrounding oxygen, is a glaze layer. The glaze layer created on the ceramic seems homogeneous at microscale but evidences a nanostructure of metallic 20 nm crystalline grains embedded in an amorphous oxidized matrix. This structure is similar in the layer adhering on the alloy but the matrix is crystalline, suggesting that the amorphization is promoted by ceramic elements. The main wear process argued is the wrenching of metallic grains that undergo further grinding without recrystallization, associated with diffusion and selective oxidation of some metallic elements. [ABSTRACT FROM AUTHOR]