The Structure and Bond Strength of Composite Carbide Coatings (WC-Co + Ni) Deposited on Ductile Cast Iron by Thermal Spraying

An investigation was conducted to determine the role of Ni particles in the WC-Co coating produced with the supersonic method on microstructure, mechanical, and wear properties in a system of type: WC-Co coating/ductile cast iron. The microstructure of the thermal-sprayed WC-Co + Ni coating was characterized by scanning electron and transmission electron microscopes as well as the analysis of chemical and phase composition in microareas (EDS, XRD). The microstructure of the WC-Co + Ni coating consisted of large, partially molten Ni particles and very fine grains of WC embedded in cobalt matrix, coming to the size of nanocrystalline. Moreover, the results were discussed in reference to examination of bending strength considering cracking and delamination in the system of (WC-Co + Ni)/ductile cast iron as well as hardness and wear resistance of the coating. It was found that the addition of Ni particles was significantly increase resistance to cracking and wear behavior in the studied system.     

Microstructure and Adhesion Strength of Ni<Subscript>3</Subscript>Ti Coating Prepared by Mechanical Alloying and HVOF

In the present work we report the development of Ni₃Ti intermetallic compound by high energy ball milling of Ni and Ti powders. The ball milled powders were taken at various intervals (4, 6, 8, 10, and 11 h) to analyze the formation of Ni _x Ti _x intermetallic compounds. The ball milled powders were analyzed using scanning electron microscopy and X-ray diffraction. The layered shaped powder particles of Ni₃Ti phase were formed after 11 h of ball milling, which was confirmed by X-ray peaks. Further High-Velocity Oxy-Fuel (HVOF) process was used to coat Ni₃Ti and Ni₃Ti + (Cr₃C₂ + 20NiCr) on MDN 420 steel. Both the coated materials displayed excellent cohesion with minimal porosity less than 2%. The tensile adhesion strength test was carried out on these coatings to check the bond strength. Out of the two the Ni₃Ti coating showed excellent bond strength of 41.04 MPa compared to that of Ni₃Ti + (Cr₃C₂ + 20NiCr) coating.     

Characterization of Microstructure and Wear Resistance of PEO Coatings Containing Various Microparticles on Ti6Al4V Alloy

Titania-based composite coatings were prepared by plasma electrolytic oxidation (PEO) treatment of Ti6Al4V alloy in electrolyte with α-Al₂O₃, Cr₂O₃ or h-BN microparticles in suspension. The microstructure, composition of PEO composite coatings were analyzed by SEM, EDS and XRD. The wear resistance of composite ceramic coatings was studied by ball-on-disk wear test at ambient temperature and 300 °C. The results showed that the addition of microparticles accelerated the growth rate of PEO coating and changed the microstructure and composition of PEO coating. PEO coating was porous and mainly composed of rutile-TiO₂, anatase-TiO₂ and Al₂TiO₅. PEO/α-Al₂O₃ (Cr₂O₃ or h-BN) composite coating only had small micropores and appeared some α-Al₂O₃ (Cr₂O₃ or h-BN) phase. Besides, the addition of α-Al₂O₃ (Cr₂O₃ or h-BN) microparticles greatly improved the wear resistance of PEO coating. At ambient temperature, abrasive wear dominated the wear behavior of PEO coating, but abrasive wear and adhesive peel simultaneously happened at 300 °C. Whether at ambient temperature or 300 °C, PEO composite coating had better wear resistance than PEO coating. Besides, PEO/h-BN composite coating outperformed other composite coatings regardless of the temperature.     

High-Temperature Erosive Behavior of Plasma Sprayed Cr<Subscript>3</Subscript>C<Subscript>2</Subscript>-NiCr/Cenosphere Coating

This research examines the deposition of Cr₃C₂-NiCr/cenosphere and Cr₃C₂-NiCr coatings on MDN 321 steel through the process of plasma spray. In this process, the solid particle erosion test is established at 200, 400, 600 °C with 30° and 90° impact angles. Alumina erodent is adopted to investigate the erosive behavior of the coating at higher temperatures. The properties of the Cr₃C₂-NiCr/cenosphere coating are established based on the microhardness, the adhesive strength, the fracture toughness, and the ductility. To quantify volume loss as a result of erosion, an optical profilometer is used. At higher temperature, decrease in the erosion volume loss of Cr₃C₂-NiCr/cenosphere and Cr₃C₂-NiCr coatings is observed. The erosion-resistive property of Cr₃C₂-NiCr/cenosphere coating is higher than that of MDN 321 steel by 76%. This property is influenced by high-temperature stability of mullite, alumina, and protective oxide layer that is formed at elevated temperatures. The morphology of eroded coating discloses a brittle mode of material removal.     

Magnetoresistive properties of Ni-doped La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> manganites

La_0.7Sr_0.3Mn_1?x Ni _x O₃ (x = 0, 0.025, 0.050 and 0.075) ceramics were prepared by the conventional solid-state reaction method. The partial substitution of Mn by Ni²⁺ leads to a decrease in cell volume as well as a structural transition from the rhombohedral to the orthorhombic structure. Ni²⁺ doping increases the electrical resistivity, decreases the semiconductor–metal transition temperature (T _ms) and relatively enhances the room temperature magnetoresistance (MR), especially in x = 0.025 and around T _ms. With respect to conduction mechanism, the small polaron hopping (SPH) and the variable range hopping (VRH) models were used to examine conduction in the semiconducting region.     

Properties of the Ti<Subscript>40</Subscript>Zr<Subscript>10</Subscript>Cu<Subscript>36</Subscript>Pd<Subscript>14</Subscript> BMG Modified by Sn and Nb Additions

The results of investigation of the influence of additions of 2 and 3 at.% of Sn and simultaneously of Sn and 3 at.% Nb on microstructure and properties of the bulk metallic glasses of composition (Ti₄₀Cu_36?x Zr₁₀Pd₁₄Sn _x )_100?y Nb _y are reported. It was found that the additions of Sn increased the temperatures of glass transition (T _g), primary crystallization (T _x ), melting, and liquidus as well as supercooled liquid range (ΔT) and glass forming ability (GFA). The nanohardness and elastic modulus decreased in alloys with 2 and 3 at.% Sn additions, revealing similar values. The 3 at.% Nb addition to the Sn-containing amorphous phase decreased as well all the T _g, T _x , T _L, and T _m temperatures as ΔT and GFA; however, relatively larger values of this parameters in alloys containing larger Sn content were preserved. In difference to the previously published results, in the case of the amorphous alloys containing small Nb and Sn additions, a noticeable amount of the quenched-in crystalline phases was not confirmed, at least of the micrometric sizes. In the case of the alloys containing Sn or both Sn and Nb, two slightly different amorphous phase compositions were detected, suggesting separation in the liquid phase. Phase composition of the alloys determined after amorphous phase crystallization was similar for all compositions. The phases Cu₈Zr_3, CuTiZr, and Pd₃Zr were mainly identified in the proportions dependent on the alloy compositions.     

Superconducting cellular MgB<Subscript>2</Subscript>

A new composite superconducting material in the form of a cellular structure consisting of large Mg grains surrounded by thin MgB₂ layers has been prepared. The superconducting properties of such a cellular structure were found to depend on the thickness of the superconducting layer d _s. As d _s decreases from ～30 to 1 μm, the critical temperature decreases by more than 10 K. The derivative of the upper critical field with respect to the temperature (dH _c2/dT) near T _c increases from ～0.2 T/K at high d _s to ～0.35 T/K at d _s ～6 μm. The critical current density of the cellular samples calculated for the area of the superconductor section is above 10⁵ A/cm² (T = 4.2 K and H = 1 T).     

Tribological Properties of HVOF-Sprayed TiB<Subscript>2</Subscript>-NiCr Coatings with Agglomerated Feedstocks

Boride materials have drawn great attention in surface engineering field, owing to their high hardness and good wear resistance. In our previous work, a plasma-sprayed TiB₂-based cermet coating was deposited, but the coating toughness was significantly influenced by the formation of a brittle ternary phase (Ni₂₀Ti₃B₆) derived from the reaction between TiB₂ and metal binder. In order to suppress such a reaction occurred in the high-temperature spraying process, the high-velocity oxygen-fuel spraying technique was applied to prepare the TiB₂-NiCr coating. Emphasis was paid on the microstructure, the mechanical properties, and the sliding wearing performance of the coating. The result showed that the HVOF-sprayed coating mainly consisted of hard ceramic particles including TiB₂, CrB, and the binder phase. No evidence of Ni₂₀Ti₃B₆ phase was found in the coating. The mechanical properties of HVOF-sprayed TiB₂-NiCr coating were comparable to the conventional Cr₃C₂-NiCr coating. The frictional coefficient of the TiB₂-NiCr coating was lower than the Cr₃C₂-NiCr coating when sliding against a bearing steel ball.     

The effects of pH and citric acid concentration on the characteristics of nanocrystalline NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> powder synthesized by a sol-gel autocombustion method

We have performed a qualitative analysis of the band structure of DyNi₂B₂C using the LDA + U method. The special structure of the antiferromagnetic order has a stabilizing effect on the superconductivity of the Ni 3d _xy band which is due to the canceling of four Dy moments nearest to each Ni site, which agrees with the phenomenological theory.     

Short-range atomic order in Fe<Subscript>2</Subscript>B powders

The possibility of application of a local atomic displacement (LAD) model for describing the mechanism of formation of a low-field part (H _hf ≤ 23.6 T) of a hyperfine-field distribution P(H) in a Fe₂B alloy at early stages of grain refinement has been investigated. It has been found that the appearance of Mössbauer contributions, which are not typical of the tetragonal C16 structure, in the P(H) function of the Fe₂B alloy is induced by a decrease in the relative interatomic distances Δr _Fe-B/r _Fe-B to ≤0.18 for some configurations of iron and boron atoms in the unit cell.     

Transport phenomena in the La<Subscript>0.72</Subscript>Ba<Subscript>0.28</Subscript>MnO<Subscript>3</Subscript> single crystal

Results of an experimental study of the temperature dependences of the magnetization M, electrical resistivity, magnetoresistance, thermo-and magnetothermo-emf, and Hall effect of the La_0.72Ba_0.28MnO₃ single crystal are presented. An analysis of the temperature dependences of kinetic properties shows that, at low temperatures, electrons are principal charge carriers in La_0.72Ba_0.28MnO₃ and the metallic conduction takes place. As the temperature increases to T ≈ 145 K, the sign of the ordinary Hall coefficient reverses; this indicates the change in the type of the majority charge carriers. Within a certain temperature range which lies substantially below the Curie temperature (T _C ), a metal-semiconductor transition occurs. Near the Curie temperature and within the paramagnetic range, the manganite under study is a semiconductor; the conduction is mainly effected by holes activated to the mobility edge. The critical behavior of the resistance and magnetoresistance is discussed.     

Corrosion Behavior and Microhardness of Ni-P-SiO<Subscript>2</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nano-composite Coatings on Magnesium Alloy

In the present work, nano-composites of Ni-P-SiO₂-Al₂O₃ were coated on AZ91HP magnesium alloy. The surface morphology of the nano-composite coating was studied by field emission scanning electron microscopy (FESEM). The amount of SiO₂ in the coating was determined by energy-dispersive analysis of x-ray (EDX), and the crystalline structure of the coating was examined by x-ray diffractometer (XRD). All the experiments concerning the corrosion behavior of the coating carried out in 3.5 wt.% NaCl solution and evaluated by electrochemical impedance spectroscopy (EIS) and polarization technique. The results showed that an incorporation of SiO₂ and Al₂O₃ in Ni-P coating at the SiO₂ concentration of 10 g/Land 14 g/LAl₂O₃ led to the lowest corrosion rate (i _corr = 1.3 µA/cm²), the most positive E _corr and maximum microhardness (496 VH). Furthermore, Ni-P-SiO₂-Al₂O₃ nano-composite coating possesses less porosity than that in Ni-P coating, resulting in improving corrosion resistance.     

Structure,magnetic and magnetocaloric properties of nonstoichiometric TbCo<Subscript>2</Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> compounds

The structure and magnetic and magnetocaloric properties of new nonstoichiometric TbCo₂Ni _x compounds (0 ≤ x ≤ 0.4) have been studied. The alloys with х ≤ 0.1 have been shown to be single-phase with the MgCu₂-type structure; in alloys with х > 0.1, an additional phase with a PuNi₃-type structure has been formed. It has been found that the concentration dependences of the Curie temperature and magnetic moment of the 3d-metal sublattice have a maximum at x = 0.025. The magnetocaloric effect magnitude for the TbCo2Nix compounds has been estimated using the results of magnetic and heat-capacity measurements.     

WC-Co and Cr<Subscript>3</Subscript>C<Subscript>2</Subscript>-NiCr Coatings in Low- and High-Stress Abrasive Conditions

The article deals with the evaluation of abrasive wear resistance and adhesive strength of thermally sprayed coatings. The main attention was paid to differences between low- and high-stress abrasive conditions of the measuring. Conclusions include the evaluation of specific properties of the WC-Co and the Cr₃C₂-NiCr High Velocity Oxygen Fuel coatings and the evaluation of the changes in the behavior of the abrasive media. Mainly, the relationship between the low- and high-stress abrasion conditions and the wear mechanism in the tested materials was described. For the wear test, the abrasive media of Al₂O₃ and SiO₂ sands were chosen. During wear tests, the volume loss of the tested materials and the surface roughness of the wear tracks were measured. The wear tracks on the tested materials and abrasive sands’ morphologies were observed using Scanning Electron Microscopy. It was found that high-stress abrasive conditions change the coatings’ behavior very significantly, particularly that of the Cr₃C₂-NiCr coating. Adhesive-cohesive properties of the coatings and relationships among individual structure particles were evaluated using tensile testing. It was found that the weak bond strength among the individual splats, structure particles, and phases plays a role in the poor wear resistance of the coatings.     

Features of the thermal behavior of PMMA/C<Subscript>60</Subscript> film composites

Polymethylmethacrylate-based film composites containing small additives of fullerenes (up to 3 wt %) are obtained. The thermal behavior of the obtained materials is studied by DSC in the temperature range from 25 to 130°C. It is found that the character of the DSC curve depends on the composite composition. For films containing up to 0.1 wt % C₆₀, one glass transition temperature (T _g ^soft) is observed, while in the case of films with a higher concentration of the filler, two glass transition temperatures (T _g ^soft and T _g ^solid) are observed. It is found that the dependence of T _g ^soft value on the content of fullerenes is nonmonotonic with a minimum at 0.5 wt % of C60.     

Effect of compaction method on the structure and properties of bulk Cu + Cr<Subscript>3</Subscript>C<Subscript>2</Subscript> composites

Cu + Cr₃C₂ composites have been produced using the mechanical alloying of the elemental components, followed by severe plastic deformation by torsion, magnetic-pulse pressing, and electric-pulse plasma sintering. The composites are studied using X-ray diffraction and light and electron microscopy, as well as measurements of the hardness, density, and electric conductivity. Magnetic-pulse pressing at a temperature of 500°C makes it possible to produce volume nanocomposites with a homogeneous distribution of dispersed carbides over the copper matrix, which has a density of 96%, a Vickers microhardness of 4.6 GPa, a Rockwell hardness of 69 HRA, and an electric conductivity of 19% IACS units. Using electric-pulse plasma sintering at a temperature of 700°C, composites with the nanostructured copper matrix, which contains carbide inclusions and consists of domains surrounded by a layer of nearly pure copper, have been produced. These composites have a density of 88%, a Vickers microhardness of 4.0 GPa, a Rockwell hardness of 58 HRA, and electric conductivity of 26% IACS units.     

Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiC Composite Prepared by Spark Plasma Sintering Process: Evaluation of Mechanical and Tribological Properties

Al₂O₃-10TiC composites were synthesized by spark plasma sintering (SPS) process. Microstructural and mechanical properties of the composite reveal homogeneous distribution of the fine TiC particles in the matrix. The samples were produced with different sintering temperature, and it shows that the hardness and density gradually increases with increasing sintering temperature. Abrasion wear test result reveals that the composite sintered at 1500 °C shows high abrasion resistance (wt. loss ~ 0.016 g) and the lowest abrasion resistance was observed for the composite sample sintered at 1100 °C (wt. loss ~ 1.459 g). The profilometry surface roughness study shows that sample sintered at 1100 °C shows maximum roughness (R_a = 6.53 µm) compared to the sample sintered at 1500 °C (R_a = 0.66 µm) corroborating the abrasion wear test results.     

Effects of hBN Content on the Microstructure and Properties of Atmospheric Plasma-Sprayed NiCr/Cr<Subscript>3</Subscript>C<Subscript>2</Subscript>-hBN Composite Coatings

NiCr/Cr₃C₂-hBN composite coatings with different contents of hBN were prepared by atmospheric plasma-spray technology. The microstructural, mechanical, and tribological properties of the coatings were systematically investigated. The results show that the flowability and apparent density of NiCr/Cr₃C₂-hBN composite powders, as well as the microhardness and tensile strength of the NiCr/Cr₃C₂-hBN composite coating, gradually decrease with the increase of hBN in the composite powders. The addition of hBN is benefit to the friction coefficient of the coatings, but it is positive to the wear rate. When the content of hBN is up to 20%, the friction coefficient of the composite coating is lowest, but the wear rate of the composite coating is highest.     

Effect of partial substitution of calcium for yttrium on the structure and properties of the Y<Subscript>0.9</Subscript>Ca<Subscript>0.1</Subscript>Ba<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6.8</Subscript> superconductor

The crystal structure of the high-temperature Y_1–xCa_xBa₂Cu₃O_6.8 superconductor has been studied in a temperature range of 80–300 K using low-temperature X-ray diffraction analysis; its microstructure has been studied by scanning and transmission electron microscopy. Changes of the bond length in the structure of principal phase and precipitation topology of impurity phases and their compositions have been analyzed. An addition of calcium was shown to increase the environmental tolerance of the principal Y123 phase and its microhardness and ensures the low unchanged coefficient of thermal expansion. All of the facts indicate that the material can be used to manufacture composite superconducting articles.