Preparation of bulky amorphous Zr-Al-Co-Ni-Cu alloys by copper mold casting and their thermal and mechanical properties

Abstract

Bulky amorphous alloys were found to form in Zr-Al-M (M = Co, Ni, Cu) systems by arc melting on a copper hearth. The largest thickness for glass formation is 6.1 mm for Zr60Al10Co3Ni9Cu18, 6.8 mm for Zr60Al15Co5Ni15Cu5 and 6.2 mm for Zr55Al20Co17.5Ni2.5Cu5. The optimum composition for glass-forming ability shifts from the Cu-rich side to the Co-rich side through the Ni-rich side with increasing Al content from 10 to 20%. The use of a metallic mold casting process enabled the formation of amorphous cylinders with the largest diameter of 7 mm for the three alloys. The compositional effect for the large glass-forming ability has also been discussed by taking the present data into consideration. The cast amorphous Zr60Al10Co3Ni9Cu18 alloy subjected to tensile testing exhibits distinct serrated flow before final fracture. The generation of the serrated flow is noticed because the alloy has a ductile nature which enables the momentary stop of the shear sliding. The Young's modulus, tensile fracture strength and fracture elongation are 97 GPa, 1510 MPa and 2.0%, respectively. The fracture occurs along the maximum shear plane and the fracture surface consists of a well-developed vein pattern. The size of their veins is about 10 times as large as that for the melt-spun ribbon and hence the shear deformation region occurs in a much wider region for the cast alloy, indicating the necessity of a larger amount of energy up to final fracture. The finding of the amorphous alloys with the large glass-forming ability and the extremely ductile nature is important for the subsequent development of metallic glassy materials.