A Ti-6Al-4V titanium alloy exhibits low hardness and poor wear resistance under sliding contact. This study evaluates the effect of low-pressure gas oxynitriding (LPON) followed by low-temperature oxidation on its microstructure and tribological performance. Specimens were nitrided at 1000 °C for 100 min, then oxidized at 450–600 °C for 120 min. Microstructural and phase changes were characterized by SEM and XRD; surface roughness, hardness, and wear were assessed using 3D laser scanning microscopy, microhardness profiling, and pin-on-disk tests under 2 N and 4 N loads. XRD revealed TiN, Ti₂N, Ti₂AlN, and TiO₂ phases, with oxidation temperature governing TiN grain growth and nitride-to-oxide transformation. Oxidation at 500–550 °C formed a dense TiO₂-rich layer over a stable TiN/Ti₂N substrate, achieving hardness up to ~670 HV_0.025 and the lowest wear volume. At low load (2 N), nitriding alone provided the highest wear resistance, while at higher load (4 N), oxidation yielded only slight improvement due to oxide embrittlement. Excessive oxidation at 600 °C increased roughness, induced spallation, and reduced wear resistance. The optimal condition (550 °C) offered synergistic protection from nitrides and stable oxides, enhancing load-bearing capacity. Overall, duplex nitriding–oxidation is most effective for low-to-moderate load applications, with potential use in biomedical implants, aerospace fasteners, and precision components.

Aluminum-air battery is a kind of energy storage device that use aluminum metal as the negative electrode material and oxygen in the atmosphere as positive reactant, and it is also usually called a power generation device of semi-fuel cell. Among the potential next-generation candidates, Ag catalysts are promising due to their high activity and low cost, but weaker oxygen adsorption has hindered industrialization. To address this bottleneck, Ag-alloying has emerged as a principal strategy. In this work, we successfully synthesized uniformly dispersed silver-coated copper (Cu@Ag) particles with BET surface areas ranging from 0.880 to 1.489 m ² /g using a chemical displacement method, and applied them as catalysts with inherent oxygen reduction reaction (ORR) activity in metal-air batteries. Cu@Ag particles was mixed with MnO ₂ in various ratios of 10:0 to 0:10. Results showed that 5 wt% Ag content yielded optimal thermal stability, and the best Cu@Ag:MnO ₂ ratio was 3:7 that demonstrated the highest ORR activity by using CV analysis, with reduction potentials of −0.121 V and −0.124 V at scan rates of 20 and 50 mV/s, respectively. These findings suggest that Cu@Ag enhances catalytic efficiency and can improve power output in metal–air batteries.

In this study, a low-pressure gas nitriding technique was employed to fabricate a nitride layer with strong interfacial bonding on the surface of Ti-6Al-4V titanium alloy. The microstructure of the modified surface layer was characterized using metallographic analysis and X-ray diffraction (XRD), while its adhesion, hardness, and wear resistance were systematically evaluated. The results demonstrated that vacuum nitriding led to the formation of a uniform and dense nitride layer composed primarily of TiN and Ti2N phases. This layer exhibited fine nitride particles and excellent metallurgical bonding with the substrate. The surface hardness reached values exceeding HV0.205 750, with a core hardness of approximately 300–320 HV and an effective hardened depth of 60–110 μm. Notably, a maximum surface hardness of HV0.025 1098 was achieved after nitriding at 1000 °C for 130 minutes. The significant increase in hardness is attributed to the formation and enrichment of hard nitride phases as nitriding time increases. However, extended nitriding duration also led to a slight rise in wear volume under a 4 N load. Compared to the untreated alloy, the nitrided specimens showed markedly improved wear resistance. At a nitriding temperature of 1000 °C, the average wear volume under conditions of 2 N for 100 minutes and 4 N for 60 minutes was 0.152 mm ³ and 1.869 mm ³ , respectively, indicating a substantial reduction in material loss.