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 Zr 60 Al 10 Co 3 Ni 9 Cu 18 , 6.8 mm for Zr 60 Al 15 Co 5 Ni 15 Cu 5 and 6.2 mm for Zr 55 Al 20 Co 17.5 Ni 2.5 Cu 5 . 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 Zr 60 Al 10 Co 3 Ni 9 Cu 18 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.