Abstract:
Metallic glasses exhibit unique properties due to their unusual amorphous microstructure. Because they do not possess slip systems and lattice dislocations as in crystalline materials, metallic glasses manifest large elastic deformation before yielding and show high yield stresses [1]. Bulk glassy/nanostructured Ti-based multicomponent alloys are attractive advanced high-strength materials for structural and functional applications, e.g. aerospace and biomedical industries [2]. Typically, the specific strength, elastic strain limits and corrosion resistance of such alloys are significantly higher than for conventional microcrystalline materials. However, the glass-forming ability (GFA) of titanium alloys is poor compared with other easy glass-forming alloys (e.g. Zr-, Cu-, Pd-, Fe-based alloys).
In this work we report on the structural competition and glass formation in two Ti-based systems with different GFA: Ti-Cu-Ni-Sn-Si-B and Ti-Zr-Si. The microstructures in the Ti50Cu20Ni24Sn3Si2B1 glass-forming alloy were tailored by melt-spinning and copper mold casting into different sizes. A glassy phase dominates in the as-spun ribbon, while the as-cast Ø2 and Ø3 mm rods are metallic glass matrix composites composed of micrometer-sized bcc NiTi dendrites surrounded by a thin metallic glass network as well as a fine distribution of CuTi3 intermetallics. The glass-forming ability, thermal stability and microstructural characteristics of as-cast rods and melt-spun ribbons were investigated by differential scanning calorimetry (DSC), X-ray diffraction and transmission electron microscopy. Crystallization behavior of Ti-Cu-Ni-Sn-Si-B and Ti-Zr-Si glassy ribbons was investigated by viscosity measurements and DSC in the mode of isochronal and isothermal annealing. The viscosity was measured by parallel plate rheometry in a large time and temperature range and compared with the DSC measurements near the glass transition temperature.
Support by the EC (FP7 VitriMetTech-ITN) is gratefully acknowledged.
[1] A.L. Greer, Materials Today 12 (2009) 14
[3] M. Calin, A. Gebert, A.C. Ghinea, P.F. Gostin, S. Abdi, C. Mickel, J. Eckert, Mat.Sci.Eng. C 33 (2013) 875-883
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