Optimal glass-forming composition and its correlation with eutectic reaction in the Ti-Ni-Al ternary system

The composition dependence of glass-forming ability was investigated for the Ti-Ni-Al ternary alloys. Glassy ribbons were fabricated via single-roller melt spinning. The optimal glass-forming composition was located at Ti₅₄Ni₃₂Al₁₄, with a critical thickness of about 90 μm for complete glass formation. With respect to the Ti-Ni binary alloy, Al addition in the system only marginally improves the glass-forming ability. It is attributed to a small atomic size difference between Ti and Al. For the Ti₅₄Ni₃₂Al₁₄ alloy, together with the binary eutectic Ti₇₆Ni₂₄ and hypereutectic Ti₆₈Ni₃₂ alloys for comparison, phase selection in the arc-melted ingots was investigated. The optimal glass-forming composition, Ti₅₄Ni₃₂Al₁₄, is near the univariant eutectic groove of [L → Ti(Al)₂Ni + β-Ti(Al)] in the phase diagram. It is suggested that if the primary crystallization of the Ti₂Ni intermetallic can be suppressed, solidification of deeply undercooled melt will undergo such a eutectic reaction prior to glass formation.