From the quaternary Ti-Zr-Hf-Ni phase diagram, the cross-section at 20 at. % Ni was selected for investigation. The icosahedral quasicrystalline, crystalline and amorphous phases were observed to form in nine kinds of rapidly solidified (Ti Zr Hf)80Ni20 (+ + =1) alloys at different compositions. The quasilattice constants of 0.519 and 0.531 nm were obtained for the icosahedral phase formed in the melt-spun Ti40Zr 20Hf20Ni20 and Ti20Zr 40Hf20Ni20 alloys, respectively. The icosahedral phase formed in the melt-spun Ti40Zr20Hf 20Ni20 alloy especially is thermodynamically stable. The supercooled liquid region of the Ti20Zr20Hf 40Ni20 glassy alloy reached 64 K. From these results a comparison of quasicrystal-forming and glass-forming abilities was carried out. The quasicrystal-forming ability was reduced and glass-forming ability was improved with an increase in Hf and Zr contents in the (Ti Zr Hf) 80Ni20 alloys. On the other hand, an increase in Ti content caused an improvement in quasicrystal-forming ability.
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