Investigation of mechanical properties and devitrification of Cu-based bulk glass formers alloyed with noble metals

The mechanical properties, glass-forming ability, supercooled liquid region and devitrification behaviour of the Cu-Zr-Ti-(Pd, Ag, Pt and Au) bulk glass formers were studied by using a mechanical testing machine, X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and isothermal calorimetry. The bulk glassy alloys of diameter 2 mm were formed in the Cu₅₅Zr₃₀Ti₁₀Pd₅ and Cu₅₅Zr₃₀Ti₁₀Ag₅ alloys while Cu₅₅Zr₃₀Ti₁₀Au₅ bulk alloy showed mixed glassy and crystalline structure. No glassy phase was formed in the Cu₅₅Zr₃₀Ti₁₀Pt₅ bulk alloy whereas the glassy phase was formed in all of the ribbon samples prepared by rapid solidification. The studied alloys except for the Pt-bearing one have slightly increased compressive fracture or yield strength values compared to ternary Cu₆₀Zr₃₀Ti₁₀ glassy alloy. At the same time Pd and Au addition significantly expand the supercooled liquid region of Cu-Zr-Ti glassy alloy and increase Young's modulus. A nanoicosahedral phase is primarily formed in the Cu₅₅Zr₃₀Ti₁₀(Pd,Au)₅ glassy alloys in the initial stage of the devitrification process by nucleation and three-dimensional diffusion-controlled growth. Nearly the same quasilattice constant obtained in the Cu₅₅Zr₃₀Ti ₁₀(Pd,Au)₅ alloys illustrates the same type of the icosahedral phase in these alloys. However, no icosahedral phase was found in the Cu₅₅Zr₃₀Ti₁₀(Ag,Pt)₅ alloys.