Abstract
Glassy ribbons of Zr65Al7.5Ni10Cu17.5‒xAux (x = 6‒17.5 at%), cold-rolled at liquid-nitrogen temperature, transform into glass and icosahedral quasicrystalline [glass’ + (IQ)] or [glass’ + IQ + dodecagonal quasicrystalline (DoQ) + approximant crystalline (APC)] phases. The rolled ribbons show plasticity, an unprecedented contrast to the extreme brittleness of all alloys containing large size IQ-, DoQ- and APC particles reported to date. After thickness reductions (R) of 50‒70%, the structure is [glass' + IQ] for 6‒15Au and [glass' + IQ + DoQ + APC] phases for 17.5Au. The IQ and DoQ particle diameters are 50‒100 nm and 150‒200 nm, respectively, much larger than the 10‒15 nm for the IQ phase when induced by annealing. On cold-rolling, the Vickers hardness decreases by up to 24% at R = 70%, in contrast to the hardening effect of annealing-induced transformation. Tensile tests on cold-rolled ribbons show evidence for preferential slip at pre-existing shear bands. The rolling-induced quasicrystalline phases have quasiperiodic atomic arrangements that are incompletely developed and do not extend over long range; the high density of internal defects and strains appears to promote plasticity. The success in synthesizing plastic [glass’ + IQ] and [glass’ + DoQ + APC] alloys may provide a new method for ductilization of brittle materials, and is promising for the development of a new type of structural material.
Highlights
Metallic materials consist of up to three types of phases with crystalline, glassy, or quasicrystalline atomic configurations
Metallic glasses can be cast in bulk form with maximum diameter above 1 cm in a wide variety of alloy systems, and they possess several properties that are attractive compared to their crystalline counterparts [3,4,5,6], e.g. higher strength, elastic strain, electrical resistivity, thermal expansion coefficient, surface smoothness, optical reflectivity, corrosion resistance, viscous deformability, and net-shape
The amorphicity of the samples was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM)
Summary
Metallic materials consist of up to three types of phases with crystalline, glassy (amorphous), or quasicrystalline atomic configurations. Metallic glasses can be cast in bulk form with maximum diameter above 1 cm in a wide variety of alloy systems, and they possess several properties that are attractive compared to their crystalline counterparts [3,4,5,6], e.g. higher strength, elastic strain, electrical resistivity, thermal expansion coefficient, surface smoothness, optical reflectivity, corrosion resistance, viscous deformability, and net-shape castability due to the much smaller shrinkage during solidification. IQ alloys show very high hardness, high wear resistance and electrical resistivity, and low thermal conductivity in comparison with conventional crystalline alloys [9,10,11]. These properties of IQ alloys may be attractive, their ultra-high brittleness has precluded their development as practical engineering materials. This brittleness is thought to originate from the difficulty of dislocation movement in the quasiperiodic lattice and from the strong covalent nature of the bonding between their constituent elements [9,10,11]
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