Bulk amorphous Co-Ni-based alloys with a large supercooled liquid region

Abstract

An amorphous alloy with a large supercooled liquid region above 80 K was synthesized for Ni40Co20Fe5Cr5Mo5Nb 5P14B6. The glass transition temperature (Tg), crystallization temperature (Tx) and melting temperature (Tm) of the amorphous alloy are 710, 791 and 1162 K, respectively, and the reduced glass transition temperature (Tg/Tm) is as high as 0.61. The amorphous alloy crystallizes through a single exothermic reaction and the crystallized structure consists of Ni, Ni3B, Ni3P, Cr3P, Ni6Mo2P and CO12Nb2P7 phases. The high thermal stability of supercooled liquid results from the crystallization mode requiring the necessity of long-range redistribution of alloy components. By use of the alloy with the high Tg/Tm value, bulk amorphous alloy rods were prepared in the diameter range up to 1 mm by copper mold casting. No difference in the thermal stability and crystallization mode is recognized for the amorphous rods. The tensile fracture strength and elongation of the amorphous alloy rod with a diameter of 1 mm are 2800 MPa and 1.88%, respectively. The tensile fracture takes place along the shear-type fracture mode and its surface consists mainly of a well-developed vein pattern. The extension of bulk amorphous alloys to the Ni-Co-based system is encouraging for the future prospect of bulk amorphous alloys as basic science and engineering materials. ©2000 The Japan Institute of Metals.