Simultaneous amorphous and nanocrystalline surface layers formation in tantalum by high-temperature ultrasonic nanocrystal surface modification treatment

High-temperature ultrasonic nanocrystal surface modification (HT-UNSM) at 450 °C was applied to tantalum (Ta) to induce severe surface plastic deformation (S 2 PD), producing a simultaneous amorphous/nanocrystalline layer confirmed by transmission electron microscopy (TEM) and fast Fourier transform (FFT) diffraction analysis. X-ray diffraction (XRD) further confirmed nanocrystallization of the α-Ta phase and complete elimination of the metastable β-Ta phase. The duplex architecture is attributed to extreme contact-pressure-driven amorphization at the surface and thermally-assisted dynamic nanocrystallization in the subsurface, demonstrating HT-UNSM as an effective strategy for tailoring near-surface microstructure and mechanical performance.