Effect of Additional Elements on Glass Transition Behavior and Glass Formation Tendency of Zr–Al–Cu–Ni Alloys

Abstract

The glass transition temperature (T_g) and crystallization temperature (T_x) of the Zr₆₅Al₁₀Cu₁₅Ni₁₀ base glassy alloys containing additional M (M=Ti, Hf, V, Nb, Cr, Mo, Fe, Co, Pd or Ag) elements were examined as a function of M elements, with the aim of finding an effective element for the increase in ΔT_x (=T_x−T_g) and of confirming the appropriateness of the previous empirical rules for the appearance of large ΔT_x. As the additional amount of the M elements except Hf increases, T_g increases gradually, whereas T_x decreases significantly and leads to the decrease in ΔT_x. No effective M element leading to the increase in ΔT_x is found. The ineffectiveness is attributed to the partial generation of repulsive bonding nature of Cu–M (M=V, Nb, Cr, Mo, Fe, Co, Pd or Ag) and Zr–M (M=Ti of Hf) pairs which does not satisfy the empirical rules. The area ratio of the glassy region in the arc-melted ingots with a maximum thickness of about 8 mm was found to increase from 67% for the Zr–Al–Cu–Ni alloy to about 90% for the Zr-based alloys containing 5%Ti, 2.5%Nb or 5%Pd, though ΔT_x decreases significantly by the addition of these elements. The great effectiveness of the three elements on the glass-formation tendency in the arc-melted ingots is interpreted to originate from the suppression of the growth reaction of crystalline nulcei which pre-exist in the arc-melted alloy. Furthermore, the disagreement between the glass-formation tendency evaluated by ΔT_x and the area ratio of the glassy region is thought to result from the difference in the dominant factors which are the crystalline nucleation and growth reactions for the ΔT_x of the melt-spun glassy alloys and the growth reaction for the area ratio of the glassy region in the arc-melted ingot. The finding of the additional elements leading to the increase in the glass-formation tendency of the arc-melted alloys, regardless of the magnitude of ΔT_x, seems to be a very encouraging event for future development of bulk glassy alloys.