Powder Metallurgy and Metal Ceramics最新文献

The TC4 (Ti6Al4V) titanium alloy fabricated by Selective Laser Melting (SLM) has gained significant attention in recent years due to its exceptional properties, including high strength-toweight ratio, excellent corrosion resistance, and biocompatibility. This study examines the effect of heat treatment on the microstructure, phase composition, and mechanical properties of SLMfabricated TC4 alloy, to provide a more comprehensive understanding of the material's behavior under varying thermal conditions. Experimental results demonstrated that the as-deposited TC4 alloy has a relative density above 0.99. The as-deposited TC4 alloy was mainly composed of closepacked hexagonal structure α/ α′ phases. In addition, a small amount of β-phase was also detected. After annealing treatment, the TC4 alloy showed a similar phase composition. The microstructure of the as-deposited TC4 alloy was composed of acicular martensite a′phase accompanied by α-phase in β-matrix. After annealing treatment, the acicular α′ martensite decomposed, transforming the microstructure into a lamellar structure consisting of α- and β-phases. The microhardness was to 351.7 HV_0.2, the tensile strength was approximately 1,120 MPa, and the yield strength comprised approximately 1,080 MPa of the TC4 alloy fabricated by SLM. The tensile fracture surface of the asdeposited alloy demonstrated a mixture of brittle and ductile fracture. A quasi-cleavage river pattern and a small amount of irregular dimples can be observed. After annealing treatment, the elongation increased to 16.5% due to a slight decrease in hardness and tensile strength. The Vickers hardness was 323.1 HV_0.2, the tensile strength was approximately 960 MPa, and the yield strength was about 925 MPa, respectively. The amounts and the size of dimples increased significantly and displayed typical ductile fracture. This research would provide valuable insights into optimizing the performance of SLM-fabricated TC4 alloys for various engineering applications.

The paper presents a comprehensive analysis of leading trends in nickel powder production techniques. The physical and technological properties of nickel powders are systematized according to chemical composition, average size and morphology of particles and their agglomerates, specific surface area, and apparent density. These data will be useful to potential consumers for the optimal design of functional properties of nickel powder products. The review compares industrial and modern techniques, focusing on their key advantages and disadvantages. The development of new process methods and techniques, such as reduction of nickel oxides with hydrogen in fluidized bed reactors and rotary furnaces, is demonstrated. Various methods for synthesizing nanosized nickel powders for special applications, being at the laboratory research stage, are considered. These methods include deposition and thermal decomposition from solutions using various precursors, synthesis under microwave radiation, laser ablation, plasma chemical synthesis, green synthesis, etc. The properties of powders produced by the reduction of nickel precursors with hydrazine, alkali metal borohydrides, polyols, urotropine, polystyrene, etc. are analyzed. Environmetal and human health concerns related to nickel powder production methods are briefly discussed. Carbonyl, electrolytic, and hydrometallurgical methods allow the production of nickel powders in large quantities but involve high energy consumption and production toxicity. Wet chemistry methods for producing nanosized nickel powders use various toxic chemical reagents, potentially causing environmental issues when implemented industrially. Hydrogen reduction of nickel oxide, as an environmentally friendly method, offers unconditional advantages, including reduced greenhouse gas emissions and zero solvent waste.

The thermal processes of recrystallization in porous copper compacts heated after cold pressing in a steel die were experimentally studied. The recrystallization stages, with temperatures corresponding to data determined with metallographic and other research methods, were identified. Only the first tempering stage was found to occur uniformly throughout the entire volume at a heating temperature of 190°C. Upon further heating, a linear stage ensued, where the temperature remained consistent throughout the entire volume of the material, persisting until the next stage. This was accompanied with energy release, as confirmed by a zero temperature gradient across all regions within the sample. With an increase in temperature to 210–215°C, a thermal surge was observed and visible temperature asynchronization was noted in individual volumes of the sample. However, this was followed by a temperature gradient between individual volumes. At this stage, asynchronized thermal behavior within the sample was observed for the first time, as evidenced by the emergence of thermal waves. Subsequent stages demonstrated nonlinear thermal behavior, evidenced by several competing processes leading to the wave-like transfer of energy accumulated as the copper powders deformed during cold pressing. Like recrystallization processes with first-order reactions in the high-temperature synthesis of intermetallic and other compounds, the emergence of thermal waves was due to several competing processes. Thus, if microplastic deformation processes occurred during recrystallization, then traveling waves could arise in the system, which was actually revealed. This could lead to thermal interference and subsequently to local buildup of thermal energy, potentially causing a sharp increase in temperature in individual areas of the wires deformed during switching and, as a result, their ignition. The temperature surges observed were likely to cause the combustion of insulating materials. Therefore, this can explain the causes of accidents that occur in the operation of complex mechanisms with numerous electrical circuits.

Al laminates are widely used in various applications due to their light weight, corrosion resistance, and good electrical conductivity. In this work, aluminum laminates were reinforced with glass fibers and a boron nitride (BN) epoxy resin. Different concentrations of BN (0, 0.3, 0.6, 0.9, and 1.2 wt.%) were incorporated into the epoxy matrix. The laminates were prepared using a vacuum infusion process (VIP) technique. The addition of BN significantly improved the thermal conductivity of the composites. To further improve the interfacial adhesion between the aluminum alloy sheets and the composite layers, plasma surface treatment was applied to the 6061-T6 aluminum alloy sheets. Plasma surface treatment is a well-known technique that can modify the surface properties of materials, including roughness, wettability, and chemical functionality. By introducing surface roughness and functional groups, plasma treatment can improve adhesion between dissimilar materials. After plasma treatment, the surface morphology and composition of the aluminum alloy sheets were analyzed using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive spectrometry (SEM-EDS). XPS provides information about the chemical composition and bonding state of the surface, while SEM-EDS provides a detailed view of the surface morphology and elemental distribution. Surface roughness and wettability were measured using a surface roughness tester and a contact angle goniometer. The Al/GF/BN/EP laminates were prepared using a thermoforming technique. Mechanical properties including peel, interlaminar shear, tensile, and flexural strength were evaluated. The laminates prepared by plasma surface treatment showed improved mechanical properties with increasing BN concentration up to 0.9 wt.%. This improvement can be attributed to the synergistic mechanism of mechanical and chemical bonding between the metal layer and the composite layer, which is facilitated by the increased surface roughness and the presence of functional groups (C–N and C=N).

The processes occurring in the simultaneous contact of ZrO₂ ceramics with two metal melts, inert (Cu, Cu–Ga, Ge, Cu–Ge) and active (Cu–Ga–Ti, Cu–Ti), were studied. The experiments were conducted in a high vacuum using thin ZrO₂ ceramic plates, with one side in contact with a droplet of active melt and the opposite side with a droplet of inert melt. In the simultaneous interaction of active and inert metal melts with zirconium dioxide, the interface processes showed mutual influence: oxygen-deficient zirconium dioxide (ZrO_2–x) was formed through the absorption of oxygen from ZrO₂ by the active melt. This contributed to the dissolution of zirconium from the solid oxide in the inert melt, thereby activating it and increasing its adhesion to the substrate. At the same time, the dissolution of zirconium in the inert melt reduced the oxygen deficiency in zirconium dioxide, i.e., restoring its stoichiometry and promoting further absorption of oxygen by the active melt. Thus, with the simultaneous contact of active and inert melts with ZrO₂, a larger amount of oxygen dissolves in the active melt, which leads to the saturation of the active melt with oxygen. This results in effects such as the loss of metallic luster and spherical shape of droplets in the active melt, delamination of the active melt, and increase in the thickness of the transition layers at the interface between the active melt and ZrO₂. The results are significantly influenced by the amounts of inert and active melts in contact with ZrO₂ and by the concentration of the active component (titanium) in the system. The results can be used in the development of methods for brazing and metallization of ceramic materials and techniques for the manufacture and use of refractories and high-temperature electrochemical devices.

In this study, the surface extrusion densification process is used to improve the surface density, hardness, and mechanical strength of powder metallurgy gears. A mixture of pre-alloyed powders, 0.3 wt.% graphite, and 0.4 wt.% Lube HD lubricant was used as experimental raw materials. These powders were compacted into experimental gears at a pressure of 1,600 MPa and then sintered at 1,120°C for 30 minutes. The sintered gears achieved surface densification by passing through extrusion dies under pressure at a 1 mm/sec speed. The influence of different extrusion amounts (∆W = 0, 0.046, 0.116, 0.186, and 0.246 mm) on the microstructure and mechanical properties of iron-based powder metallurgy gears was investigated (∆W is defined as the reduction in the cross- bar distance between two teeth in the extrusion die plate). The results show that surface densification by extrusion can simultaneously apply normal stress and shear stress, resulting in a reduction of porosity on the gear surface, which in turn forms a densified layer on the surface. The thickness of the densified layer increases with the amount of extrusion. In addition, the surface densification by extrusion improves the surface microhardness and crushing strength of the gears. In particular, the gears with ∆W = 0.246 mm have the highest surface microhardness and fracture toughness. The porous model in DEFORM was used to simulate the surface extrusion densification process. The simulation results showed trends in the relative density distribution consistent with the experimental results, with a higher relative density at the gear surface, followed by a decrease as the distance from the surface increased and the densified region expanded with increasing extrusion amounts. In addition, there was a high degree of correlation between the simulated and experimental results in terms of densification layer thickness.

Thermal barrier coatings (TBCs) play a critical role in protecting metallic substrates from high-temperature degradation in aerospace and industrial applications. This study was undertaken to synthesize and evaluate a novel lanthanum phosphate zirconate (LaPZ) composite as a potential candidate for TBCs. The LaPZ composite was synthesized by a high-energy ball milling method followed by calcination, which allows precise control over the composition and microstructure. The synthesized LaPZ composite was characterized by various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermal analysis. Lanthanum phosphate was prepared by precipitation method: calcined at 700°C and further calcined at 1,200°C for 2 h. LP-C was used for the preparation of composite powders. It was ball milled at 350 rpm for 8 h, wet milled with distilled water in a high energy planetary mill with zirconia media, and calcined at 1,300°C for 4 h. X-ray diffraction analysis at 1,300°C revealed LaPZ composite powders with a cubic pyrochlore structure of La₂Zr₂O₇ and monoclinic LaPO₄. To obtain the pyrochlore structure, LaP and zirconia were taken in two different molar ratios, namely 1 : 1 (LaPZ 1) and 1 : 2 (LaPZ 2). The coefficient of thermal expansion (CTE) of the LaPZ 1 coating was approximately 8.97 · 10^–6 K^–1. The LAPZ 2 coating exhibited a CTE of 9.15 · 10^–6 K^–1 when exposed to temperatures ranging from 0 to 1,400°C. Samples maintained stable thermal expansion up to 1,400°C, indicating the suitability of LaPZ for TBC applications.

The influence of detonation spraying parameters on the porosity and adhesion of (Ti, Cr)C–Ni coatings was studied. These detonation coatings were applied from (Ti, Cr)C-based composite powders containing 18, 25, and 33 wt.% Ni onto a steel substrate. The particle-size distribution of the powders was –63+40 μm. A Dnipro-5M installation was used for detonation spraying. The flow rate of acetylene and oxygen, the air pressure for ejecting detonation products, and the spraying distance were varied in the spraying process. The structure of the coatings was examined by optical microscopy and electron probe microanalysis. The adhesion of the (Ti, Cr)C–Ni coatings was determined by the pin method, and the porosity was measured by the linear Rosival method. In the detonation spraying of (Ti, Cr)C–Ni composite powders, particles of double titanium–chromium carbide refined to 6–7 μm, contributing to the development of a fine and uniform structure of the detonation coatings. It was found that the detonation spraying parameters should be adjusted upward when the nickel content changed from 18 to 33 wt.% in the (Ti, Cr)C–Ni composite powders. The increase in the nickel content from 18 to 33 wt.% resulted in higher adhesive strength and lower porosity of the coatings. In the research, an acceptable level of adhesive strength and porosity could not be reached for the (Ti, Cr)C–18 wt.% Ni detonation coating. The (Ti, Cr)C–33 wt.% Ni detonation coating exhibited the highest adhesive strength (101 MPa) and the lowest porosity (2%) among the studied coatings and is thus promising for further research of its tribological properties.

The isoperibolic calorimetry method was used to determine the mixing enthalpy of liquid alloys in the Ni–Tb system in the composition range 0 < x_Ni < 0.6 at 1660 ± 1 K. The minimum mixing enthalpy of melts in this system was –41.8 ± 0.9 kJ/mol at x_Ni = 0.6. The activities of components and the mole fractions of associates in these melts were calculated according to the ideal associated solution (IAS) model with our and literature values of formation enthalpies for compounds in the Ni–Tb system and with phase diagram data. Two associates were selected for the calculations: TbNi and TbNi₅. The activities of the components showed large negative deviations from the ideal solution, with the simplest associate, TbNi, being predominant (x_max = 0.65). The second associate was present in a much smaller proportion (x_max = 0.22). These data correlate with the mixing enthalpies of the melts, formed with significant exothermic effects. To assess the reliability of the formation enthalpies of compounds and melts in the Ni–Tb system, they were compared with those of LnNi₅ compounds and liquid alloys in the Ni–Ln system. All were determined with different options of the calorimetry method. Hence, to be compared, they were plotted as a function of the Ln atomic number. Most of the data points aligned with two trend lines, except for the data for compounds in binary Ni–Gd(Dy, Er) systems and melts in binary Ni–Ce (Eu, Yb) systems. Regarding these ΔH_min values, which are more exothermic (Ni–Ce system) and less exothermic (Ni–Eu(Yb) systems) than all others, they may be attributed to the electronic structures of atoms in the components of the melts. The Eu and Yb atoms are known to have half-filled and completely filled 4f orbitals, while the Ce atom contains one electron in the 4f orbital. Therefore, Eu and Yb are divalent and Ce is tetravalent in the nickel alloys. Since nickel is a strong electron acceptor, the energy of its interaction with Ce is greater and that with Eu and Yb is lower compared to other neighboring lanthanides.

This paper considers the dependence of the thermodynamic properties of glass-forming liquid alloys of the (Fe, Co, Ni, Cu)–Ti–Zr systems on composition and temperature. The associate solution model (ASM) was used as a calculation tool. The results of the calculations correspond to the experimental data on the integral mixing enthalpy, presented in the first part of the work, and reveal the regularities of changes in other thermodynamic functions and the features of interaction between components in these liquid alloys. It was established that the excess thermodynamic mixing functions in each system have negative values, which are determined by pair interactions between Fe, Co, Ni, and Cu as electron acceptors and Ti and Zr as electron donors. The trend of changes in the minimum values of excess thermodynamic mixing functions of the systems shows an increase in their absolute values along the 3d-series from iron to nickel and a significant decrease for copper, which corresponds to a change in the acceptor capacity of metals along the transition series. The temperature dependence of the thermodynamic mixing functions consists in an increase in negative deviations from ideality and an increase in the intensity of interaction between components with a decrease in temperature. The formation of glass-forming liquid alloys from pure metals is accompanied by an increase in the thermodynamic stability of the liquid phase, which is reflected in negative values of the Gibbs mixing energy. In the range of 800–1873 K, the Δ_mG function of liquid equiatomic alloys of the systems considered shows values at the level of –20...–35 kJ/mol. Within the framework of ASM, using the total mole fraction of associates as a quantitative estimate of the degree of short-range chemical order, it is shown that liquid alloys of the Me–Ti–Zr system are characterized by significant chemical ordering, which increases with decreasing temperature. Using the empirical rule, the experimentally known compositions of amorphous alloys for the Cu–Ti–Zr and Ni–Ti–Zr systems were interpreted and the composition regions of liquid alloy amorphization were predicted for the Fe–Ti–Zr and Co–Ti–Zr systems.