Effect of additional elements on glass transition behavior and glass formation tendency of Zr-Al-Cu-Ni alloys

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 Delta T-x (=T-x-T-g) and of confirming the appropriateness of the previous empirical rules for the appearance of large Delta T-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 Delta T-x. No effective M element leading to the increase in Delta T-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 are-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 Delta T-x decreases significantly by the addition of these elements. The great effectiveness of the three elements on the glass-formation tendency in the are-melted ingots is interpreted to originate from the suppression of the growth reaction of crystalline nulcei which pre-exist in the are-melted alloy. Furthermore, the disagreement be tween the glass-formation tendency evaluated by Delta T-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 Delta T-x of the melt-spun glassy alloys and the growth reaction for the area ratio of the glassy region in the are-melted ingot. The finding of the additional elements leading to the increase in the glass-formation tendency of the are-melted alloys, regardless of the magnitude of Delta T-x, seems to be a very encouraging event for future development of bulk glassy alloys.