To improve the AlCoCrFeNi high entropy alloys’ (HEAs’) toughness, it was coated with different amounts of Cu then fabricated by the powder metallurgy technique. Mechanical alloying of equiatomic AlCoCrFeNi HEAs for 25 h preceded the coating process. The established powder samples were sintered at different temperatures in a vacuum furnace. The HEAs samples sintered at 950 °C exhibit the highest relative density. The AlCoCrFeNi HEAs model sample was not successfully produced by the applied method due to the low melting point of aluminum. The Al element’s problem disappeared due to encapsulating it with a copper layer during the coating process. Because the atomic radius of the copper metal (0.1278 nm) is less than the atomic radius of the aluminum metal (0.1431 nm) and nearly equal to the rest of the other elements (Co, Cr, Fe, and Ni), the crystal size powder and fabricated samples decreased by increasing the content of the Cu wt%. On the other hand, the lattice strain increased. The microstructure revealed that the complete diffusion between the different elements to form high entropy alloy material was not achieved. A dramatic decrease in the produced samples’ hardness was observed where it decreased from 403 HV at 5 wt% Cu to 191 HV at 20 wt% Cu. On the contrary, the compressive strength increased from 400.034 MPa at 5 wt% Cu to 599.527 MPa at 15 wt% Cu with a 49.86% increment. This increment in the compressive strength may be due to precipitating the copper metal on the particles’ surface in the nano-size, reducing the dislocations’ motion, increasing the stiffness of produced materials. The formability and toughness of the fabricated materials improved by increasing the copper’s content. The thermal expansion has increased gradually by increasing the Cu wt%.

This study investigates the influence of titanium dioxide (TiO ₂ ) incorporation (0–50 wt.%) on the structural, thermal, and tribological properties of metakaolin-based geopolymer composites (GPCs). The bulk density of the composites increased progressively from 1.81 g/cm ³ for the control sample to 2.86 g/cm ³ at 50 wt.% TiO ₂ , while apparent porosity decreased from 33.47 to 23.48%. Water absorption was correspondingly reduced from 8.43 to 5.34% after 24 h immersion, confirming the pore-filling effect of TiO ₂ . XRD and FTIR analyses indicated the coexistence of amorphous aluminosilicate gel, residual quartz, and anatase reflections, with Ti–O and Ti–O–Si vibrations confirming the physical embedding of TiO ₂ without disrupting the geopolymeric framework. SEM micrographs revealed that higher TiO ₂ content led to a denser morphology with fewer pores, confirming densification. DSC/TGA revealed that TiO ₂ addition enhanced stability and reduced low-temperature mass loss. Pin-on-disc testing showed that adding 40 wt.% TiO ₂ significantly improved tribological performance, reducing the wear rate from 3.45 × 10 ⁻⁵ to 1.12 × 10 ⁻⁵ mm ³ /N m and the steady-state friction coefficient from 0.36 to 0.29. These results confirm the dual role of TiO ₂ as a microstructural densifier and a reinforcing agent, enabling the development of geopolymer composites with enhanced durability, thermal stability, and wear resistance suitable for high-performance structural applications in extreme environments.

In this work, Porous copper foam samples were fabricated by a space-holder technique with water-atomized copper powder and sodium chloride (NaCl) particles in weight fractions ranging from 10 to 35 wt%. The powders were mechanically mixed at a 10:1 ball-to-powder ratio and 150 rpm for 2 h. The effects of space-holder content on the physical, mechanical, tribological, and electrochemical performance were systematically investigated. Increasing the NaCl fraction precisely controlled the total porosity, from 39.15% to 57.76%, and reduced the bulk density from 5.452 to 3.785 g/cm³. XRD and SEM analyses confirmed a single-phase FCC copper matrix and a structural transition from isolated pores to a highly interconnected open-cell network. Consequently, Vickers hardness, compressive yield strength, energy absorption capacity decreased from 52.12 to 29.23 HV, 18.25 to 1.65 MPa, and 35.73 to 10.46 MJ/m³, respectively, following a modified Gibson–Ashby model (R ² = 0.95). Concurrently, the coefficient of friction and specific wear rate increased (reaching a maximum of 0.73 mm³/N·m under 15 N for 35 wt% NaCl) due to strut thinning and localized delamination. Electrochemical evaluation in 3.5 wt% NaCl solution revealed an optimization threshold for sample fabricated with 25 wt% NaCl, which exhibited the lowest corrosion rate of 0.918 mm/y, and the highest polarization resistance (Rp) of 267.28 Ω, due to a stable Cu ₂ O passive film. Exceeding this threshold at 30 and 35 wt% NaCl led to structural instability and stagnant electrolyte zones, accelerating corrosion kinetics. Overall, lower-porosity porous copper foam architectures offer superior structural energy absorption, whereas the 25 wt% NaCl configuration achieves an optimal balance between mechanical integrity and corrosion resistance.