Production of Zr55Cu30Ni5Al10 Glassy Alloy Rod of 30 mm in Diameter by a Cap-Cast Technique
used for the preparation of the master alloy. The purity of these metals; Zr(+Hf), Cu, Ni and Al were 99.99 mass%, 99.999 mass%, 99.99 mass% and 99.999 mass%, respectively. The alloy ingots were completely remelted, and cast into cylindrical rod samples with diameters from � 16 mm to � 30 mm by a modified cap-casting method, as shown in Fig. 1. The cap-cast technique was designed to obtain high cooling rate even at the upper part of cast specimen. The cast structure was examined by scanning electron microscopy (SEM), and the compositions of the quenched samples were determined with an electron probe microanalyzer (EPMA). The phase identification of the cast samples was performed by X-ray diffractometry. Oxygen concentration of the bulk glassy alloys was measured by a helium carrier fusioninfrared absorption. Microscopic cast structures were examined by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) using a JEOL 4000 FX. TEM samples were prepared by an electrolytic polishing machine using nitric methanol (30 vol% HNO3) at about 250 K.
Glassy solidification criterion of Zr50Cu40Al10 alloy
We examined the solidification morphology and structure of arc-melted Zr50Cu40Al10 glass-forming alloys. Since the crystal growth rate is much lower than the velocity of isothermal plane of glass transition temperature (Tg), arc-melted Zr50Cu40Al10 alloy sometimes reveals glassy phase at finally solidified region (top-side) after crystal growth (bottom side). Vitrification in front of the crystalline solidification interface of arc-melted Zr50Cu40Al10 alloy Zr can be seen when the crystal phase is an Al-supersaturated B2-type ZrCu phase.
Solidification condition of bulk glassy Zr60Al10Ni10Cu15Pd5 alloy by unidirectional arc melting
The relation between the formation of a glassy phase and the solidification parameters of moving velocity of liquid/ solid interface (V), temperature gradient (G) and cooling rate (R) was examined for a Zr 60 Al 10 Ni 10 cu 15 Pd 5 alloy, with the aim of clarifying a solidification condition for formation of a bulk glassy alloy by a unidirectional arc-melting method. The glassy phase was obtained in the condition of V> 4 mm/s, G>4 K/mm and R>40K/s. The decrease in G causes the formation of equiaxed dendrites, oriented dendrites and cell structure. The supercooling for the present alloy was measured to be as large as 385 K at a low cooling rate of 40K/s. The large supercooling ability is presumably due to the formation of a highly dense random packed structure where the nucleation of a crystalline phase and the atomic rearrangement for growth reaction are difficult. The glass formation of the present multicomponent alloy in the unidirectional arc melting method seems to be dominated by the ease of the supercooling ability rather than the achievement of high cooling rate.