Effects of Annealing and Annealing with Pressure on Devitrification of Al 87 Ni 7 Gd 6
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Effects of Annealing and Annealing with Pressure on Devitrification of Al87Ni7Gd6 Paul Wesseling, B.C. Ko, L.O. Vatamanu, J. Caris and J.J. Lewandowski Case Western Reserve University, Department of Materials Science and Engineering Cleveland, Ohio 44106, U.S.A. ABSTRACT The effects of annealing for 30 minutes at temperatures ranging from 123-232°C on the structure evolution, resulting hardness, and tensile properties were determined for amorphous ribbons of Al87Ni7Gd6. Structure evolution was determined using a combination of XRD, DSC, and TEM, while micro-hardness and tensile testing of ribbon specimens was used to evaluate the mechanical properties. Significant effects of annealing on the evolution of structure and properties were obtained, while the superposition of 940 MPa pressure during annealing further enhanced the structure evolution with corresponding changes to the resulting properties. INTRODUCTION Amorphous metals provide interesting combinations of physical and mechanical properties [1], while devitrification of the amorphous systems often produces significant changes to both the physical [1] and mechanical [1,2,3,] properties. Annealing of various Al based amorphous alloys has been shown to produce structures that range from α-Al nano-particles to coarser intermetallic particles depending on the composition and annealing temperatures under investigation [4]. The strengthening that accompanies devitrification in such systems has been proposed to arise from a number of different sources, including changes to the composition of the amorphous matrix [5], the precipitation of defect-free nano-particles [6], or combinations of such effects. Although annealing has been shown to produce embrittlement of various amorphous systems [1,3,7], this is not always observed. Recent reports on various amorphous aluminum alloys also suggest strengthening without embrittlement [6]. The present work was conducted to determine the effects of isothermal annealing for 30 minutes at different temperatures for amorphous Al87Ni7Gd6 . In addition, isothermal annealing experiments were conducted with 940 MPa superimposed pressure over the same temperature range. MATERIALS AND CHARACTERIZATION The amorphous ribbons (Al87Ni7Gd6 in at%) were produced via melt spinning using a chilled copper block at 2900 RPM [8]. The resulting ribbons had a thickness of approximately 30 µm and a width of 2.5 mm and were stored at 0°C until any experiments were conducted. Characterization was obtained by a combination of techniques. XRD (Scintag X1 apparatus) using Cu-Kα radiation was used with a scan rate of 1.2 deg/minute; thermal analysis via differential scanning calorimetry (MDSC, TA 2910) using a heating rate of 20K/min); and Transmission electron microscopy (TEM) analyses on a Philips CM20 operated at 200 kV. The TEM foils were prepared using the following solution and current settings: electro-polished at approximately -30°C in a 30% Nitric acid + 70% Methanol solution; the current and voltage settings were 0.1 A and 10V, respecti
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