首页|Structural evolution and thermal stability of functionally graded NiTi nano-glass thin films alloys during crystallization
Structural evolution and thermal stability of functionally graded NiTi nano-glass thin films alloys during crystallization
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NSTL
Elsevier
? 2022Functionally graded and composite materials are known as new materials, which exhibit higher performances and provide a comprehensive application. This paper introduces a bi-layer Ni-rich/NiTiCu alloy with a composite structure comprising nano-crystal, glassy and amorphous microstructure. The successive crystallization of amorphous Ni-rich/NiTiCu bi-layer thin films deposited at room temperature was studied by annealing at 773 K for 15, 30, and 60 min. Different experiments, including scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD), high-resolution transmission electron microscopy (HRTEM), and thermodynamics calculations (CALPHAD) were conducted to analyze the microstructure. The crystal nucleation, glassy/amorphous thermal stability against alloying elements, and related interfaces were studied. The as-deposited thin films were fully amorphous and had a rounded nano-glassy structure. HRTEM images indicated no long-range periodic lattice and the interface between layers was flat and sharp. Short-time annealing depicts non-spherical crystal nuclei in the amorphous NiTiCu layer with a diffuse interface. In contrast, after 60 min annealing, the NiTiCu and NiTi layers were fully and mostly crystallized with different structures, respectively. The results confirm the higher thermal stability of the amorphous NiTi binary alloy. Thermodynamic and diffusion studies indicate that the higher driving force of amorphous to B2 ordered structure against Cu addition along with the higher Cu diffusivity compared with Ni and Ti are responsible for lower thermal stability of NiTiCu.
NSTL
Elsevier
