The Effect of Iron and Oxygen Additions on the Properties of Zr-Al-Cu-Ni Bulk Metallic Glass Forming Alloys
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INTRODUCTION The new class of multicomponent metallic glasses with excellent glass forming ability and wide supercooled liquid region has attracted a lot of interest recently [1-31. These alloys can be prepared as bulk samples even at low cooling rates of 10 K/s or less and have considerable potential as advanced engineering materials due to their excellent processing capabilities of the supercooled liquid, low coefficient of friction, high wear resistance as well as high strength and good corrosion resistance [4]. These alloys contain highly reactive elements and oxygen or metallic contaminations are frequently present already in the starting constituents, e.g. transition metal or rare earth elements. Furthermore, contaminations might also be introduced during alloy preparation by quenching or solid state processing. For example, mechanically alloyed powders typically contain some iron impurities due to the wear debris of the steel milling tools [5, 6]. In the past evidence has built up that for instance already a small amount of oxygen significantly affects the glass transition and crystallization behavior of metallic glasses [7, 8]. However, no detailed understanding of the role of contaminations on the properties of bulk metallic glass forming alloys exists up to now. The aim of this paper is to study the influence of iron and oxygen additions on the glass transition and crystallization behavior of the bulk metallic glass forming Zr 65A17.5CU17 .5Ni1 0 alloy in some detail for different iron and oxygen contents. EXPERIMENTAL METHODS Prealloyed ingots were molten from pure elements (purity 99.9%) in an arc furnace under a Ti-gettered argon atmosphere. Amorphous ribbons 10 mm in width were quenched by singleroller melt-spinning in a Buihler melt-spinning device under argon. The oxygen containing alloys were prepared by adjusting the oxygen partial pressure upon arc-melting and melt-spinning. 465 Mat. Res. Soc. Symp. Proc. Vol. 455 © 1997 Materials Research Society
Thermal analysis was performed in a Netzsch DSC 404 differential scanning calorimeter at a heating rate of 20 K/mmn in purified argon. X-ray diffraction patterns were measured with a Philips PW3020 Bragg-Brentano diffractometer equipped with a secondary graphite monochromator using CuKa radiation. Chemical analysis was done by electron microprobe analysis, atomic absorption spectroscopy, hot extraction and optical emission spectroscopy.
RESULTS AND DISCUSSION Figure 1 shows x-ray diffraction patterns for as-quenched Zr'65 A1T 5Cu1 7 5Nit0 ribbons with different iron or oxygen content. All diffraction patterns exhibit only the typical broad diffuse maxima characteristic of an amorphous phase. No indication for crystalline phases is evident in the x-ray patterns, even for large iron contents. The scattering vector Qp related to the position of the first diffuse maximum between 300 < 20 < 50° and defined as Qp= 4rtsin90 m~/, shifts to larger values with increasing Fe content (Fig. 2). A linear extrapolation to 100% Fe gives Qp =
31 nm~t which is simila
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