Influence of helium ion irradiation on the mechanical properties of high-entropy (Hf,Ta,Ti,V,Zr)-nitride, -carbide and -diboride thin films: A comparative study

Abstract

In this study, high-entropy (Hf, Ta, Ti, V, Zr)- nitride, -carbide, and -diboride thin films were synthesized via magnetron sputtering and implanted with helium ions using a helium ion microscope. All films exhibited a stable single-phase structure, with no amorphization observed even at high ion fluences. At a helium ion dose of 5 × 10^17 ions/cm^2, volumetric swelling was 15.1 ± 0.8 % for the carbide, comparable to that of tungsten, but lower for the nitride (10.7 ± 1.2 %) and diboride (11.7 ± 0.5 %). Initial hardness values were 26.9 ± 1.3 GPa for the nitride, 32.4 ± 1.5 GPa for the carbide, and 38.9 ± 0.7 GPa for the diboride, where the strongest decrease upon irradiation was observed for the carbide (ΔH = -38 ± 7 % at 5 × 10^17 ions/cm^2). Compression testing revealed that, despite its brittle nature, the diboride exhibited measurable plasticity after irradiation. Fracture toughness tests revealed K_IC values of 2.83 ± 0.21 MPa√m for the nitride, 2.48 ± 0.07 MPa√m for the carbide, and 3.47 ± 0.14 MPa√m for the diboride. The carbide's low fracture toughness likely contributes to its higher mechanical degradation, attributed to inter-void fracture mechanisms.