Precipitation of icosahedral quasicrystalline phase in Hf 69.5 Al 7.5 Ni 11 Cu 12 metallic glass
- PDF / 820,001 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 15 Downloads / 205 Views
Akihisa Inoue Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Received 26 September 2000; accepted 1 February 2001)
A Hf69.5Al7.5Ni11Cu12 metallic glass was prepared by a single roller melt-spinning method, and the crystallization process was studied by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The metallic glass crystallizes through three exothermic reactions. The low-temperature exothermic reaction corresponded to the precipitation of an icosahedral quasicrystalline phase. Further annealing at higher temperature led to the decomposition of the icosahedral quasicrystalline phase to other stable crystalline phases, indicating that the precipitated icosahedral quasicrystalline phase was in a metastable state. The crystallization process of the present alloy was compared with that of other Hf–Al–Ni–Cu alloys, and the reason for the precipitation of the icosahedral quasicrystalline phase was discussed.
I. INTRODUCTION
II. EXPERIMENTAL
Recently, a Hf-based icosahedral quasicrystalline phase (I-phase) was reported, which was found in the initial crystallization processes of metallic glasses.1–3 The compositions of these Hf-based glassy alloys are analogous to those of the well-known Zr-based metallic glasses. In the Zr–Al–Ni–Cu alloy system, Inoue et al. reported the preparation of cylindrical bulk glassy alloys with diameters of 16 and 30 mm, corresponding to the compositions of Zr55Al10Ni5Cu304 and Zr65Al7.5Ni10Cu17.5,5 respectively. It has been found that the partial substitution of Cu by noble metals (Pd, Pt, Au, and Ag) in Zr65Al7.5Ni10Cu17.5 leads to the precipitation of the Iphase in the initial crystallization process.6–8 From the similarity between Hf and Zr, the crystallization process of Hf65Al7.5Ni10Cu12.5Pd52 and Hf65Al7.5Ni10Cu17.59 metallic glasses has been studied. The initial precipitation phases are an I-phase and a face-centered cubic Hf2Ni (fcc-Hf2Ni) phase for the former and later alloys, respectively. To clarify the possibility of I-phase formation in the Hf–Al–Ni–Cu alloy system without the addition of Pd, several amorphous alloys have been prepared and their crystallization process has been studied. Precipitation of an I-phase in Hf69.5Al7.5Ni11Cu12 metallic glass was revealed, and the result is reported in this paper.
The alloy ingot with nominal atomic percent composition of Hf69.5Al7.5Ni11Cu12 was prepared by arc melting a mixture of pure metals. From the alloy ingot, a ribbon with a cross section of about 0.03 × 1 mm2 was prepared by a single roller melt-spinning method in an argon atmosphere. The melt-spun ribbon was annealed in an evacuated quartz tube. The structure was examined by x-ray diffraction (XRD), and the thermal stability was investigated by differential scanning calorimetry (DSC) at a heating rate of 0.67 K/s. The microstructure was examined with a transmission electron microscope (TEM) JEM-3000F (JEOL, Tokyo, Japan) operated at 300 kV. The diameter of the electron beam was focused to 1.0 and 2.4
Data Loading...
