Oxidation and crystallization of an amorphous Zr 60 Al 15 Ni 25 alloy
- PDF / 267,024 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 87 Downloads / 257 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Oxidation and crystallization of an amorphous Zr60 Al15 Ni25 alloy X. Sun, S. Schneider, U. Geyer, W. L. Johnson, and M-A. Nicolet California Institute of Technology, Pasadena, California 91125 (Received 23 January, 1995; accepted 5 June, 1996)
The amorphous ternary metallic alloy Zr60 Al15 Ni25 was oxidized in dry oxygen in the temperature range 310 ±C to 410 ±C. Rutherford backscattering (RBS) and cross-sectional transmission electron microscopy (TEM) studies suggest that during this treatment an amorphous layer of zirconium-aluminum-oxide is formed at the surface. Nickel was depleted in the oxide and enriched in the amorphous alloy near the interface. The oxide layer thickness grows parabolically with annealing duration, with a transport constant of 2.8 3 1025 m2ys 3 exps21.7 eVykTd. The oxidation rate may be controlled by the diffusion of Ni in the amorphous alloy. At later stages of the oxidation process, precipitates of nanocrystalline ZrO2 appear in the oxide near the interface. Finally, two intermetallic phases nucleate and grow simultaneously in the alloy, one at the interface and one within the alloy. An explanation involving preferential oxidation is proposed.
I. INTRODUCTION
Recently, a novel group of amorphous metallic alloys such as ZrAlNi,1 ZrAlCu,2 ZrAlNiCu,3 and ZrTiNiCuBe4 with excellent glass-forming ability and high thermal stability has been discovered. Most of these alloys are Zr-based, and highly reactive with oxygen. It is therefore of general interest and practical relevance to study the mechanism of oxidation and its influence on nucleation of crystalline phases near the glass transition temperature. The present study examines the temperature-dependent oxidation behavior of the amorphous Zr60 Al15 Ni25 alloy. II. EXPERIMENTAL
Zr60 Al15 Ni25 ingots were prepared by induction melting on a water-cooled copper boat under a Tigettered argon atmosphere. Small pieces of the initial ingot were levitation-melted in a high-frequency rf field. The samples were subsequently quenched into thin foils in a pure argon-filled twin-piston rapid quencher. The thickness of these quenched foils is about 50 mm. The foils were exposed to dry oxygen in an openended quartz-tube furnace over a temperature range of 310 ±C to 410 ±C. The oxygen gas flow was adjusted to 100 cm3ymin. Other samples were annealed in a vacuum-tube furnace with a base pressure of 4 3 1027 Torr. Rutherford backscattering spectrometry (RBS) was performed to analyze the concentration depth profiles using 2.0 MeV and 6.2 MeV 4 He21 ions. RBS data analysis was performed using the standard procedures.5 In order to study the structure of the as-quenched and annealed foils, x-ray diffraction using Co Ka radiation (l 0.1790 nm) was applied. The microstructure and composition of the samples were also studied by TEM 2738
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 11, Nov 1996
Downloaded: 14 Mar 2015
and analyzed by energy-dispersive analysis of x-rays (EDS). These samples were pre
Data Loading...
