Effects of B upon glass forming ability of Al87Y8Ni5 amorphous alloy

In this study, 15 at.% of boron is added to increase the thermal stability and amorphous forming ability of Al87Y8Ni5 alloy ribbons by single roller melt-spinning process. Thermal properties including crystallization activation energy and the Avrami exponent of crystallization are investigated using non-isothermal and isothermal analyses. Only the (Al87Y8Ni5)85B15 amorphous alloy ribbon demonstrates a glass transition temperature (Tg) at 529 K, and its ΔTx (=Tx − Tg) value is 24.6 K. Crystallization kinetic study show that the 15 at.% of boron increases the activation energy for crystallization from 159 to 228 kJ/mol. The Avrami exponent n value of Al87Y8Ni5 amorphous alloy is 1.5 ∼ 2.1 indicating a decreasing nucleation rate with crystallization time, whereas the n value of (Al87Y8Ni5)85B15 amorphous alloy ribbon is 2.3 ∼ 3.1 or the nucleation rate increases with time. The addition of boron could affect the crystal symmetry in atomic clusters and thus the phase separation behavior in the amorphous alloy. Boron is shown to delay the nucleation of boron-containing Al nano-crystals in crystallization. The maximum hardness is obtained for both non-boron and boron added alloys after crystallization at 592–596 K region due to formation of nano-crystallites. The highest hardness achieved is 575 and 595 Hv for Al87Y8Ni5 and (Al87Y8Ni5)85B15 alloys, respectively. Both the Al nano-crystals and solute-rich amorphous phase formed by phase separation contribute to the hardness increase.

• 15 at.% boron added to Al87Y8Ni5 alloy demonstrates glass transition in contrast to its non-boron opponent.
• A large 24.6 K ΔTx (Tx−Tg) liquid supercooling range indicates (Al87Y8Ni5)85B15 a possible ductile Al-based amorphous alloy.
• Boron is effective in improving thermal stability of Al87Y8Ni5 amorphous alloy by increasing the activation energy for crystallization by 43%.
• The hardness in crystallization of the boron-containing alloy could achieve as high as 595 Hv.
• Boron could affect the short-range and medium-range symmetry which delays the nucleation and crystallization kinetics.