Powder Metallurgy and Metal Ceramics最新文献

In this study, the creep behavior, mechanical properties, and microstructure evolution of AA 1050/SiC/Cu composite strips fabricated by accumulative roll bonding (ARB) process are experimentally investigated. All specimens were fabricated with different SiC wt.% with a maximum of eight cumulative cycles of ARB. The study of creep behavior and mechanical properties showed the formation of a 17 μm atomic diffusion layer at the interface during ARB under three creep loading conditions, namely 35 MPa at 225°C, 35 MPa at 275°C, and 30 MPa at 225°C. An intermetallic compound formed near Al, resulting in a 40% increase in interface thickness with increasing temperature at constant stress. However, the creep failure time decreased by 44% and the stress level decreased by 13% at a constant temperature without any significant effect on the interface thickness. In different conditions, it was observed that at a constant temperature with an increase in stress level, the second steady state creep rate of the creep curve reaches to 39%, while it decreases to 2% with a small increase in temperature. It can be concluded that the applied temperature and stress affect the creep properties and especially lead to an increase in the steady-state creep rate of the creep curves with higher stresses. This trend was the opposite for the creep temperature at higher temperature levels. Furthermore, dynamic recrystallization was observed through the crystalline structure of the samples.

The tribotechnical properties of the Cu–(4–6) wt.% Ni–(1–1.5) wt.% Ti–(7–10) wt.% Al–(0.5–0.8) wt.% Si‒(5–8) wt.% CaF₂ antifriction composite were studied. The effect of tribofilms that form and evolve in the friction process in air at loads of 2.0 MPa and rotational speeds from 5,000 to 15,000 rpm on the tribological properties was analyzed. The evolution of dissipative tribofilms and the counterface occurs through a bifurcation mechanism with a transition to one of two attractors, depending directly on the high-speed loading modes. At speeds of 5,000–13,000 rpm, a continuous homogeneous lubricating layer forms on the contacting surfaces. Electron microscopy and elemental mapping of the tribofilm confirmed that the distribution of elements was uniform, promoting high antifriction properties and a sustained self-lubrication mode. With increase in the rotational speed to 15,000 rpm, the system exhibits a self-organization effect in the formation of a coarse heterogeneous tribofilm. This tribofilm loses its continuity and is an accumulation of phases, leading to a sharp decline in antifriction properties. The dual formation of tribofilms is decisively influenced by operating conditions, particularly the intensity of external energy. Depending on this energy, tribofilms show different structures and manifest in two functionally opposite types, transforming from antifriction films to friction ones, resulting in significantly different tribotechnical properties. Copper-based antifriction composites can be recommended as an effective alternative to cast bronzes for operation at rotational speeds of 5,000–13,000 rpm and loads of 2.0 MPa in the friction units of forming, printing, and offset cylinders in high-speed printing equipment.

Experimental studies were conducted to refine the theoretical provisions concerning the mechanism and kinetics of penetration for a metal melt consisting of destructive reagents, such as gallium, indium, tin, and zinc (destructive composition), along the grain boundaries in unstressed metal samples. It was experimentally confirmed that the penetration rate of the destructive composition was limited by processes at the liquid phase front, including dissolution of intergranular boundary areas, recrystallization to form solid solution crystals, and opening of new crack areas under the pressure of growing crystals. The experimental findings indicated a significant decrease in the strength of aluminum alloys resulting from the effect of the destructive composition. Analytical dependences and corresponding empirical coefficients characterizing the effects of the destructive composition on structural aluminum alloy elements under tensile loads were derived. These empirical coefficients enable the determination of conditions under which aluminum alloy structures fail under the influence of destructive compounds, considering the tensile stresses. The effect of the destructive alloy on the onset of fatigue damage and the durability of aluminum alloy structures under asymmetric cyclic stresses was examined. Significant reduction in the fatigue strength of aluminum structures under the influence of the destructive composition was experimentally confirmed.

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.