Composition design procedures of Ti-based bulk metallic glasses using the cluster-plus-glue-atom model

It is known that bulk metallic glasses are interpreted by simple composition formulas [cluster](glue atom)1 or 3, with the valence electron number per unit formula (e/u) being universally 24. In the present work, this cluster-plus-glue-atom approach was explored in great details for the objective of establishing the standard procedures towards designing bulk metallic glasses, via example of Ti-Cu-based alloys. The cluster selection from devitrification phases and the e/u calculation methods were first clarified. Then, step-by-step procedures toward developing alloys with high glass forming abilities were proposed. The cluster formula [Ti-Cu6Ti8]Cu3, with e/u ≈ 23.6, was taken as the basic composition formula. Upon properly alloying with Zr and Sn, large glass forming abilities up to 5 mm in diameter were experimentally reached at Ti40Zr10Cu56.94Sn3.06 via copper mold suction casting. Another alloy Ti45.71Zr11.43Cu39.29Sn3.57 showed a slightly inferior glass forming ability of 4 mm but contained the highest Ti(Zr) content of all the Ti-based BMGs, Ni-, Pd- and Be-free. The thus-obtained bulk metallic glasses generally exhibited high compressive strengths of about 1.8 GPa and nearly zero ductilities, except a Co-alloyed one, [Ti-Cu5.3Sn0.5Co0.2Ti6.2Zr1.8]Cu3, whose compressive ductility exceeded 6%. [Display omitted]