Comments on the Paper “Production of Zr<SUB>55</SUB>Cu<SUB>30</SUB>Ni<SUB>5</SUB>Al<SUB>10</SUB> Glassy Alloy Rod of 30 mm in Diameter by a Cap-Cast Technique” (Yoshihiko Yokoyama, Enrico Mund, Akihisa Inoue and Ludwig Schultz, Mater. Trans. 48 (2007) 3190–3192.)

Abstract

1. Summary of the Title Paper This paper describes a new casting technique and the required oxygen level for successful production of Zr55Cu30Ni5Al10 glassy alloy rod up to 30 mm in diameter. The casting technique named ‘‘cap-cast method’’ consisted of arc-melting the alloy followed by quick casting into water cooled copper mold; a copper ‘‘cap’’ is used to compress the alloy melt at 1 kN from the top surface immediately after casting. This cap is needed to prevent shrinkage cavity and to enhance the cooling speed of the alloy melt. Low oxygen level, less than 45 mass ppm in the starting zirconium metal, was required to obtain homogeneous Zr55Cu30Ni5Al10 glassy alloy rod. Otherwise, crystalline inclusions were observed in the glass matrix. It is also stated that ‘‘the formation of a single glassy phase in the half topside of master alloy’’ was confirmed for the as-arc melted button ingots, cooled naturally on the copper hearth. It is concluded that (1) the purity level of alloy component is an important factor to produce glassy alloy rods with large size and (2) the Zr55Cu30Ni5Al10 glassy alloy rods of up to 30 mm in diameter could be produced by means of the cap-cast technique; the critical size of glassy alloy rods is 20 mm by the conventional cast technique using copper molds.