Effects of Ag and Co microalloying on glass-forming abilities and plasticity of Cu-Zr-Al based bulk metallic glasses

Abstract

The influences of Ag and Co additions on the thermal stability and glass-forming abilities of twenty (Cu46-xZr47Al7Agx)100-yCoy (x = 0, 1, 2, 3, 4 and y = 0, 0.5, 1, 1.5) alloys were systematically investigated by X-ray diffraction and differential scanning calorimeter techniques. The mechanical performances (i.e., hardness, strength, and plasticity) of the alloys were evaluated, and the plasticization mechanisms of four representative (Cu46-xZr47Al7Agx)100-yCoy specimens were discussed based on the observations of scanning electron microscopy and high-resolution transmission electron microscopy. It is found that (Cu43Zr47Al7Ag3)99.5Co0.5 bulk metallic glass exhibits excellent thermal stability and improved plasticity after compression tests. The improvement can be attributed to the large amount and density of shear bands, the coexistence of a large area of smooth regions, the vein-like pattern, and the river-like pattern on the fractures. More importantly, the new-formed B2-CuZr phases and nanocrystallines during compressive tests also contribute to the improved plastic deformation ability by exalting the number and density of shear bands.