Search Results (136)

Shape memory alloys (SMAs) are known for their exceptional mechanical properties, particularly their superior wear resistance compared to conventional alloys with similar surface hardness. Rare earth oxides are often used as additives to further improve these characteristics. This study investigates the effects of different CeO₂ (cerium dioxide) concentrations (0.01 wt.%, 0.1 wt.%, 0.5 wt.%, and 1.0 wt.%) on the properties of CuAlMnFe alloys produced via powder metallurgy (PM). Various analyses were performed, including scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD), as well as hardness, wear, and corrosion tests. The increase in wear rate is closely related to the formation of precipitates from CeO₂ addition. Improvements in wear resistance and hardness are attributed to the effects of grain refinement and solid solution strengthening due to CeO₂. Specifically, the wear rate increased from 1.5 × 10⁻³ mm³/(Nm) to 3.4 × 10⁻³ mm³/(Nm) with higher CeO₂ content. Additionally, the friction coefficient of the CuAlMnFe alloy was reduced with CeO₂ addition, indicating enhanced frictional properties. The optimal CeO₂ concentration of 0.5% was found to improve grain uniformity, resulting in better wear resistance. Incorporating CeO₂ particles into CuAlMnFe alloy enhances hardness and reduces wear rate when used in appropriate amounts. Additionally, it exhibits superior corrosion resistance, as evidenced by a positive shift in corrosion potential in Tafel measurements in solutions and a decrease in corrosion current density. The C0.5 specimen showed the highest corrosion potential (E_corr, −588 V) and the lowest corrosion current density (i_corr, 6.17 μA/cm²) during electrochemical corrosion in 3.5 wt.% NaCl solution. Full article

This study synthesized FeNiCuAlX high-entropy alloys (HEAs) (where X = Cr, Co, Mn) using arc melting and investigated their high-temperature oxidation behavior in air at 900 °C. The oxidation kinetics of all alloys followed a parabolic rate, with the oxidation rate constants (kp) of FeNiCuAlCr, FeNiCuAlCo, and FeNiCuAlMn being approximately two to three orders of magnitude lower than that of the FeNiCu alloy. Specifically, FeNiCuAlCr exhibited the lowest kp value of 1.72 × 10⁻⁶ mg²·cm⁴/s, which is significantly lower than those of FeNiCuAlCo (3.29 × 10⁻⁶ mg²·cm⁴/s) and FeNiCuAlMn (1.71 × 10⁻⁵ mg²·cm⁴/s). This suggests that the addition of chromium promotes the formation of a dense Al₂O₃/Cr₂O₃ oxide layer, significantly enhancing the oxidation resistance. Furthermore, corrosion resistance was assessed through potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution. FeNiCuAlCr demonstrated exceptional resistance to localized corrosion, as indicated by its low corrosion current density (45.7 μA/cm²) and high pitting potential (−0.21 V), highlighting its superior corrosion performance. Full article

This study evaluates the wear and corrosion resistance of the Cu-50Ni-5Al alloy reinforced with CeO₂ nanoparticles for potential use as anodes in molten carbonate fuel cells (MCFCs). Cu–50Ni–5Al alloys were synthesized, with and without the incorporation of 1% CeO₂ nanoparticles, by the mechanical alloying method and spark plasma sintering (SPS). The samples were evaluated using a single scratch test with a cone-spherical diamond indenter under progressive normal loading conditions. A non-contact 3D surface profiler characterized the scratched surfaces to support the analysis. Progressive loading tests indicated a reduction of up to 50% in COF with 1% NPs, with specific values drop-ping from 0.48 in the unreinforced alloy to 0.25 in the CeO₂-doped composite at 15 N of applied load. Furthermore, the introduction of CeO₂ decreased scratch depths by 25%, indicating enhanced wear resistance. The electrochemical behavior of the samples was evaluated by electrochemical impedance spectroscopy (EIS) in a molten carbonate medium under a H₂/N₂ atmosphere at 550 °C for 120 h. Subsequently, the corrosion products were characterized using X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the CeO₂-reinforced alloy exhibits superior electro-chemical stability in molten carbonate environments (Li₂CO₃-K₂CO₃) under an H₂/N₂ atmosphere at 550 °C for 120 h. A marked reduction in polarization resistance and a pronounced re-passivation effect were observed, suggesting enhanced anodic protection. This effect is attributed to the formation of aluminum and copper oxides in both compositions, together with the appearance of NiO as the predominant phase in the materials reinforced with nanoparticles in a hydrogen-reducing atmosphere. The addition of CeO₂ nanoparticles significantly improves wear resistance and corrosion performance. Recognizing this effect is vital for creating strategies to enhance the material’s durability in challenging environments like MCFC. Full article

The metal-based/ceramic interface structure is a key research focus in science, and addressing the stability of the interface has significant scientific importance as well as economic value. In this project, the work of adhesion, heat of segregation, electronic structure, charge density, and density of states for doped-M (M = Ti, Mg, Cu, Zn, Si, Mn, or Al) Ni (111)/Al₂O₃ (0001) interface structures are studied using first-principle calculation methods. The calculation results demonstrate that doping Ti and Mg can increase the bonding strength of the Ni–Al₂O₃ interface by factors of 3.4 and 1.5, respectively. However, other dopants, such as Si, Mn, and Al, have a negative effect on the bonding of the Ni–Al₂O₃ interface. As a result, the alloying elements may be beneficial to the bonding of the Ni–Al₂O₃ interface, but they may also play an opposite role. Moreover, the Ti and Mg dopants segregate from the matrix and move to the middle position of the Ni–Al₂O₃ interface during relaxation, while other dopants exhibit a slight segregation and solid solution in the matrix. Most remarkably, the segregation behavior of Ti and Mg induced electron transfer to the middle of the interface, thereby increasing the charge density of the Ni–Al₂O₃ interface. For the optimal doped-Ti Ni–Al₂O₃ interface, bonds of Ti–O and Ti–Ni are found, which indicates that the dopant Ti generates stable compounds in the interface region, acting as a stabilizer for the interface. Consequently, selecting Ti as an additive in the fabrication of metal-based ceramic Ni–Al₂O₃ composites will contribute to prolonging the service lifetime of the composite. Full article

This study attempts to use fly ash as the brazing filler additive to increase the sustainable use of coal-fired power plant by-product materials. The experimental results show that adding 5 wt% fly ash into the Ag paste filler contributes to the interfacial reactions in heterogeneous reactive air brazing (RAB) of the ZrO₂ and Crofer alloy. The Ag-rich phase dominates the brazed zone. The interfacial reaction layers contain oxidation of the Cu-Ti coating layer, Crofer alloy, and the Si/Al-rich oxides from the fly ash particles. The 5% fly ash RAB joint maintained airtightness for 280 h under 2 psig helium at room temperature. When the test temperature was raised to 600 °C for 24 h, the pressure of the joint assembly still did not drop. When the fly ash addition was increased to 10 wt%, the joint assembly was no longer leak-free at room temperature. Many visible voids and cracks exist in the brazed zone and at the ZrO₂/braze and braze/Crofer interfaces. A high volume fraction of the fly ash particles results in many brittle Si/Al-rich oxides in the joint after RAB, and the fracture of these oxides significantly deteriorates the airtightness of the joint. This study shows the feasibility and potential of introducing 5 wt% fly ash particles to the Ag-rich paste filler during the RAB of ZrO₂ and Crofer for airtight applications. Full article

The self-healing characteristics of Al6061 reinforced with CuO have been examined experimentally. The solder alloys 60Pb40Sn and 99.3Sn0.7Cu with low melting points are incorporated to strengthen the Al6061 MMCs’; the self-healing properties have been investigated. Developed self-healing samples have undergone testing for hardness, tensile, and impact characteristics in accordance with ASTM standard test protocols. The findings demonstrate how the solder filling affects the mechanical characteristics of self-healed Al6061 alloy and its MMCs’. The results showed that the composites formed a decent bond between the solder and matrix, confirming successful fabrication. Pb-Sn filled samples demonstrated higher self-healing efficiency for tensile and impact of 90.02% and 90.30% with 6 wt.% of CuO, respectively, and Sn-Cu filled samples witnessed higher self-healing efficiency for tensile and impact of 91.81% and 91.09% with 6 wt.% of CuO respectively. However, the self-healed composite did not split in two when subjected to Charpy impact and tensile strength tests, and the healing efficiency of Sn-Cu-filled composites is higher than that of the Pb-Sn-filled composites. Full article

Sinter-based additive manufacturing (AM) requires sintering for the densification of green bodies. Al powder is difficult to sinter due to the dense oxide film on the surface, and it is difficult to apply to sinter-based AM. Liquid phase sintering using Al-based eutectic alloy powder is promising for sintering Al powder without external pressure. In this study, Al powders with various oxide film thicknesses were sintered using Al-X eutectic alloy powders (X=Cu, Ca, and Mg) to clarify suitable alloy elements in the sintering aids for the liquid phase sintering. When an as-supplied Al powder with an oxide film thickness of approximately 2 nm (presumably amorphous Al₂O₃ film) was used, Al-Cu and Al-Ca aids promoted the densification, whereas numerous pores were observed in the sample sintered using Al-Mg aid. The pores would be formed during the cooling after sintering, along with the homogenization of Mg distribution. When Al powder with an oxide film thickness of around 4 nm was used, a high relative density of over 95% was maintained using Al-Cu aid, whereas the relative density of the sample sintered using Al-Ca aid significantly degraded, presumably due to the formation of Ca-based oxide. These results indicate that the Al-Cu eutectic alloy powder is a promising sintering aid for the liquid phase sintering of Al powder. Full article

This article presented an investigation into the microstructure evolution of a hot-extruded Cu-0.23Al₂O₃ alloy during thermomechanical treatment. The results demonstrated that cold rolling deformation introduced high-density dislocations into the matrix, resulting in a significant enhancement in the strength of the Cu-0.23Al₂O₃ alloy. Subsequent annealing at 500 for 1 h led to a reduction in dislocation density in the sample. Consequently, the strength of the sample decreased very slightly, while the elongation increased from 14% to 39%. There was little growth of the nano-scale Al₂O₃ particles due to their excellent thermal stability, with the average size remaining approximately 10 nm after annealing. The comprehensive properties of the Cu-0.23Al₂O₃ alloy were improved synchronously by thermomechanical treatment, with a tensile strength of 301 MPa and an electrical conductivity of 98.5%IACS. The calculation results of the strengthening mechanism indicated that refinement strengthening, work hardening and Orowan strengthening mainly contributed to the high strength of the Cu-0.23Al₂O₃ alloy. Full article

This study systematically investigated the effects of tailored heat treatments on the microstructural evolution, mechanical properties, and erosion–corrosion resistance of Cu-10Ni-3Al-1.8Fe-0.8Mn alloy. Four heat treatment conditions—as-cast (AC-1); homogenized (H-2); and deformation–aged at 500 °C (D-3) and 750 °C (D-4)—were applied to elucidate the interplay between microstructure and performance. The D-3 specimen, subjected to deformation followed by aging at 500 °C for 0.5 h, demonstrated superior properties: a Vickers hardness of 118 HV5 (83.3% higher than H-2) and an erosion–corrosion rate of 0.0075 mm/a (84.1% reduction compared to H-2). These enhancements were attributed to the uniform dispersion of nanoscale Ni₃Al precipitates within the matrix, which optimized precipitation strengthening and reduced micro-galvanic corrosion. The D-3 specimen also formed a dense, crack-free Cu₂O corrosion product film with a flat matrix interface, confirmed by SEM cross-sectional analysis and electrochemical impedance spectroscopy (EIS), exhibiting the highest charge transfer resistance and film impedance. Full article

Advancements in electrical components have intensified the challenges for copper alloy wear resistance and high-temperature performance in electrical applications. The surface coating preparation of Cu alloys is crucial for enhancing their lifespan and promoting sustainable resource development. This study explored the microstructure and properties of Cu-Cr-X coatings (X = Mo/W, Al₂O₃/TiO₂) on Cu alloy substrates via laser-cladding to improve wear resistance and hardness, vital for electrical component reliability and switching capacity. The process involved adjusting the power and reinforcing the phase particle size. The results showed hardness > 110 HV for all coatings (vs. 67.4 HV for the substrate). Cu-Cr-W achieved the highest hardness at 179 HV due to W dispersion and WCr precipitate reinforcement. It also maintained a stable CoF and the lowest wear rate (1.87 mg/km), with a fivefold wear resistance compared to the substrate alone. Cu-Cr-W excelled in lifespan extension and material loss reduction due to superior hardness, wear resistance, and conductivity. Full article

In this study, the applicability of an Al-Si alloy with 30 wt% added scrap for automobile pistons was evaluated by investigating the melt quality, microstructural characteristics, and tensile properties under modified GBF (gas bubbling filtration) process conditions, including increasing rotor rotation speed and adjusting the air-line supply and the inclination angle of the impeller blade. The melt quality was dramatically improved under modified GBF process conditions, resulting in a very clean melt, with the D.I. value decreasing by 28%, the length of the oxide layer per kilogram decreasing by 65%, and inclusion content decreasing by 97% compared to that of the conventional GBF process conditions. Additionally, the size of primary Si decreased from 40 µm to 27 µm, and the eutectic Si and intermetallic compounds were refined, showing a very fine microstructure. The identified phases included Al₄Cu₂Mg₈Si₇, Al_xCu_yNi_z, and MgO. The ultimate tensile strength was 275 MPa, and the elongation was 6.0%, indicating improved tensile properties compared to those of the conventional GBF process conditions. The fracture behavior changed from a brittle microcleavage fracture mode to a ductile dimple fracture mode as the primary Si, eutectic Si particles, and intermetallic compounds were refined under modified GBF process conditions. These results confirmed that Al-Si alloy with added scrap can be used as a material for automobile pistons. Full article

A CuNiCe-O nanocomposite was fabricated on the Cu₄₀Ni₂₀Al₁₀Ce₂₆Pt₃Ru₁ metallic glass (MG) ribbon surface by dealloying. The influences of Ni and dealloying time on the morphology and EOR performance were analyzed. The results suggest that the catalytic activity and stability of the dealloyed MG ribbon could be significantly enhanced owing to the alloying of Ni to the Cu₆₀Al₁₀Ce₂₆Pt₃Ru₁ MG ribbon precursor. The activated D-Cu₄₀Ni₂₀Al₁₀Ce₂₆Pt₃Ru₁ ribbon obtained at an etching time of 3 h had a better electrochemical ethanol oxidation reaction (EOR) performance than other dealloyed samples due to the formation of abundant active sites and the presence of defects within the CuNiCe-O composite. Full article

To improve high-temperature oxidation resistance for Ti6Al4V alloy, Al_xCoCrCu_yFeNi (x = 0, 0.3, 0.5, 0.7, 1.0; y = 1.0, 0.7, 0.5, 0.3, 0, x + y = 1.0) high-entropy alloy (HEA) coatings were prepared on the Ti6Al4V alloy substrate by a laser cladding technique. The results show that the coatings were mainly composed of FCC, BCC, and Ti-rich phases. Severe segregation of the Cu element occurred in the CoCrCuFeNi HEA coatings as a Cu-rich phase (FCC2). The Cu-rich phases decreased with a decreasing Cu content and completely disappeared until the Al content reached 1.0. The microhardnesses of the Cu_1.0, Cu_0.7Al_0.3, Cu_0.5Al_0.5, Cu_0.3Al_0.7, and Al_1.0 HEA coatings were 2.01, 2.06, 2.08, 2.09, and 2.11 times that of the substrate, and compared with those of a Ti6Al4V alloy substrate, the oxidation rates of the HEA coatings decreased by 55%, 51%, 47%, 42%, and 35%, respectively. The surface oxides of the five coatings were mainly composed of CuO, TiO₂, Fe₃O₄, Cr₂O₃, and Al₂O₃. The increase in the Al content promoted the generation of Al₂O₃ film and Cr₂O₃ on the surfaces of the coatings, which significantly improved the high-temperature antioxidant performance of the high-entropy alloy coatings for 50 h at 800 °C. When x = 1.0, the coating showed the best high-temperature antioxidant performance. Full article

Copper matrix composites (Cu-MCs) have garnered significant attention due to their exceptional electrical, wear-resistant, and mechanical properties. Among them, Al₂O₃/Cu composites, reinforced with Al₂O₃, are a focal point in the field of high-strength, high-conductivity copper alloys, owing to their high strength, excellent electrical conductivity, and superior resistance to high-temperature softening. Cold deformation is an effective method for enhancing the mechanical properties of Al₂O₃/Cu composites. However, during cold deformation of large-cross-sectional Al₂O₃/Cu composites, the inhomogeneity in microstructure and properties induced by varying stress states cannot be overlooked. In this study, cold deformation of 1.12 wt% Al₂O₃/Cu large-cross-sectional composites was performed using a rolling process, coupled with finite element numerical simulations, to investigate the distribution characteristics of microstructure and properties during the rolling process. The results indicate that under cold deformation, the hardness of the material increases linearly from the surface layer to the core, while the change in electrical conductivity is minimal. The increase in hardness is closely related to variations in dislocation density and grain size, with dislocation density being the dominant strengthening mechanism. Quantitative analysis reveals that strain inhomogeneity during cold deformation is the primary cause of microstructural differences, leading to variations in mechanical properties at different positions. This study provides a theoretical basis for understanding the inhomogeneity of cold deformation in large-sized Al₂O₃/Cu composites and for controlling their microstructure–property relationships. Full article

Commercially pure Cu features excellent electric conductivity but low mechanical properties. In order to improve the mechanical properties of Cu, strengthening elements can be added to prepare alloys or composites featuring enhanced performances. This study focuses on the detailed characterization of the microstructure of a Cu composite strengthened with Al₂O₃ particles during high shear strain processing. The Cu-Al₂O₃ mixture was prepared by powder metallurgy and directly consolidated by the intensive plastic deformation method of hot rotary swaging. Samples cut from the consolidated piece were further processed by the severe plastic deformation method of high pressure torsion (HPT). The primary aim was to investigate the effects of varying degrees of the imposed shear strain, i.e., the number of HPT revolutions, microstructure development (grain size and morphology, texture, grain misorientations, etc.) of the consolidated composite; the microstructure observations were supplemented with measurements of Vickers microhardness. The results showed that the added oxide particles effectively hindered the movement of dislocations and aggravated grain fragmentation, which also led to the relatively high presence of grain misorientations pointing to the occurrence of residual stress within the microstructure. The high shear strain imposed into (the peripheral region of) the sample subjected to four HPT revolutions imparted equiaxed ultra-fine grains and an average Vickers microhardness of more than 130 HV0.1. Full article