Institute of Fundamental Technological Research

In this study, the AlCoCrFeNiTi0.2 high-entropy alloy (HEA) was plasma nitrided to investigate the microstructure and mechanical properties of high-entropy nitrides formed in the surface layer of the bulk sample. XRD measurements revealed a BCC → FCC crystal structure transformation, with the σ phase disappearing and hexagonal aluminum nitride emerging. Further experimental studies on the nitrided samples, including SEM, EDS, and EBSD, uncovered element segregation into multiple FCC phases with similar lattice constants, such as the NaCl-type (AlCrCoFeNiTi0.2)N high-entropy nitride. These observations align with theoretical analysis based on KKR-CPA calculations. Additionally, plasma nitriding induced high surface porosity; however, micropillar compression testing combined with nanoindentation revealed localized areas with significant hardness. A substantial reduction in the coefficient of friction was also observed. These findings not only provide deeper insights into the nitriding process of complex alloys, like dual-phase HEAs, but also hold promise for further exploration in the manufacturing of super-hard surfaces with high-entropy nitrides, enhancing mechanical properties for applications in harsh environments.

This study examines nitrogen ion implantation's effects on the microstructure, mechanical behavior, and tribological performance of an octonary high-entropy thin film metallic glass HfMoNbTaTiVWZr. Ion implantation led to binary nitride formation, elemental redistribution, and surface modifications while maintaining significant degree of amorphization, what indicates local atomic rearrangement rather than crystallization. Structural and chemical analyses using TEM, XRD, and EDS mapping revealed phase stability changes and preferential segregation of heavy elements like hafnium and tantalum at high doses. Hardness enhancement was attributed to solid solution strengthening, fine nitride formation, increased lattice distortion, residual stress, and densification. At an optimal implantation dose (1e17 ions/cm2), hardness increased to 20 GPa, reducing the coefficient of friction and improving wear resistance. A comparison with a magnetron-sputtered (HfMoNbTaTiVWZr)N thin film showed distinct hardness-depth profiles, confirming localized strengthening effects. These findings highlight nitrogen implantation as an effective surface engineering technique for optimizing material performance in demanding applications

High entropy film metallic glasses, Ion implantation, Microstructure, Indentation, Surface characteristics

High entropy alloys, high entropy nitrides, nitriding, nanoindentation, ion implantation