Effects of Changes in Chemistry and Testing Temperature on Mechanical Behavior of Al-Based Amorphous Alloy Ribbons
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INTRODUCTION
A combination of good strength and low density (i.e., specific strength) is necessary for structural materials. Significant interest has developed in amorphous and nanocrystalline aluminum alloys in recent years because of their high strength and low density.[1] The most important group of Al-based amorphous alloys are the aluminum-rare earth-transition metal (Al-RE-TM) system alloys because of their good glass-forming ability and mechanical properties.[2–4] These alloys have been shown to exhibit strengths almost twice that of conventional Al alloys (7075-T6: ry 500 MPa) with similar densities as conventional Al alloys.[1] Recent research has been investigating the effects of annealing on devitrification and the subsequent mechanical properties of an Al-Gd-Ni alloy.[3,5–7] The results showed that Al87Gd6Ni7 exhibited a low-onset crystallization temperature Tx1, 462 K (189 C), and tensile tests showed that the precipitation of pure a-Al nano particles from the glassy matrix, thereby enriching the local matrix in Gd and Ni, produced embrittlement. In the past decade, many efforts have investigated the effects of compositional changes on the thermal stability of amorphous alloys.[2,8–10] It has been shown that an increase in the amount of transition metal elements has a significant effect on Tx for Al-RE-TM amorphous alloys.[2] In this study, the effects of Fe and Co additions in an Al-Gd-Ni amorphous alloy (Al87Gd6Ni7) are represented. The flow and fracture behavior across a range of testing temperatures and strain rates is characterized. CHUN-KUO HUANG, Graduate Student, and JOHN J. LEWANDOWSKI, Leonard Case Professor of Engineering, are with the Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, USA. Contact e-mail: [email protected] Manuscript submitted November 24, 2009. Article published online May 25, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
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EXPERIMENTAL PROCEDURES
The materials (Al86Gd6Ni7Fe1, Al86Gd6Ni7Co1, Al85Gd6Ni7Fe2, and Al85Gd6Ni7Fe1Co1) were produced by Ames Laboratory (Ames, IA) via the melt spinning technique using a rotating chilled copper block at a wheel speed of 16 m/s. The melt spinning process was in a well-controlled He atmosphere of 0.3 atm. The as-received ribbons have a thickness of 50 lm and a width of 1.8 mm. The ribbons were confirmed amorphous by X-ray diffraction (XRD; X1; Scintag, Cupertino, CA) using Cu Ka radiation with a scan rate of 3 deg/min on the air side of the ribbons in addition to transmission electron microscopy (TEM) described subsequently. Thermal stability analysis was performed by differential scanning calorimetry (DSC; DSC822e; Mettler Toledo, Aurora, IL) with a heating rate of 3 K/min (3 C/min)—identical to the heating rate used in the high-temperature tensile tests. Young’s modulus was measured via the nanoindentation technique (Hysitron Triboscope, Minneapolis, MN) using a load of 2000 uN and a loading rate of 1 9 104 N/s. A Nikon QM hot microhardness tester (Nikon Instruments, Melville, NY) with a
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