Ti-based bulk metallic glasses (BMGs) have significant advantages such as high specific strength, high corrosion resistance, and relatively lower cost. But the high glass-forming ability is always combined with toxic component Be. The critical size of Ti-based alloys without Be are far away from the centimeter degree. For industrial applications, it is of great interest to develop Be-free Ti-based BMGs with high glass forming ability. Based on Ti-Cu-Sn ternary alloys, adopting the “3D pinpointing approach”, compositional dependence of glass-forming ability (GFA) for Ti-(Cu1-xNix)-Sn (0.2 x 0.3) quaternary alloys was systematically investigated. The glass-forming ability for these alloys was evaluated by using copper mold casting. X-ray diffraction, scanning electron microscopy, and differential scanning calorimetry were employed to characterize the structures and glass nature. The following conclusions are drawn:
(1) Ti-Cu-Sn Glass ribbons with 158 m thickness were obtained by melt-spinning method. With the increasing of the Sn component, the crystallization and melting behavior changed significantly. Every crystallization curve exhibits visible glass transition temperature Tg and the reduced glass transaction Trg are around 0.56. There are four phases in the arc-melting Ti49Cu45Sn6 alloy and the process of the solidifications is: LTi3Sn Ti5Sn3CuTiCuTi3Cu4. Rods with 1 mm diameter are fully crystalline.
(2) The alloy with the optimal GFA is located at Ti38Cu37.8Ni16.2Sn8. Its critical size for metallic glass formation is nearly 1 mm in diameter for the rods fabricated by using copper mold casting. This metallic glass exhibits the supercooled liquid region ∆Tx of 56 K and the reduced glass transaction temperature Trg of 0.57. By characterizing the microstructure of the arc-melted Ti38Cu37.8Ni16.2Sn8 alloy, it is indicated that solidification of the melt underwent a pseudo binary eutectic reaction of (L—〉TiCuNi+Ti5Sn3Cu).
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