Effects of ion irradiation on the microstructure and mechanical properties of titanium-based metallic glasses
Abstract
Metallic glass specimens with a nominal composition of Ti₄₀Cu₃₄-ₓPd₁₄Zr₁₀Sn2Siₓ (at.%), where x = 2, 3, and 5, were subjected to annealing and/or ion irradiation and their microstructure and mechanical properties were characterized by a combination of X-ray diffraction (XRD), transmission electron microscopy (TEM), nanoindentation, scanning probe microscopy (SPM), and atomic force microscopy (AFM). No evidence of crystallization was observed for the specimens that were annealed at temperatures below the glass transition temperature and those irradiated with 4 MeV Fe²⁺ ions at room temperature, regardless of the fluence used. Annealing at temperatures below the glass transition temperature resulted in an increase in hardness and higher plastic deformation energy values, which suggests a reduction in ductility. Conversely, ion irradiation at room temperature resulted in a reduction in reduced elastic modulus, hardness, and plastic deformation energy, which suggests an improvement in ductility. For the specimens irradiated with 3.5 MeV Cu²⁺ ions at elevated temperatures, it was found that there is a critical temperature below which the specimens remained amorphous. When ion irradiation was performed at temperatures higher than the critical temperature, the specimens crystallized to depths beyond the range of the implanted ions. This critical temperature was found to be equal to the glass transition temperature when ion beam heating was minimized. By subjecting a crystallized Ti₄₀Cu₃₁Pd₁₄Zr₁₀Sn₂Si₃ specimen to a second step irradiation with 3.5 MeV Cu²⁺ ions using a fluence of 1 x 10¹⁶ ions/cm² at room temperature a metallic glass-matrix composite containing discontinuous crystalline phases, 10 - 80 nm in diameter, was created. Formation of nanocrystals in the composite was seen to result in an increase in reduced elastic modulus and hardness, and to shift the deformation mechanism towards less shear localization and more homogenous plastic flow compared to the as-spun specimen. These observations confirm that formation of nanocrystals can promote initiation of a larger number of shear bands and inhibit shear band propagation, which could lead to an improvement in ductility.
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- OSU Dissertations [11222]