Formation, Mechanical and Electrical Properties of Ni-based Amorphous alloys and their Nanocrystalline Structure
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I10.4.1
Formation, Mechanical and Electrical Properties of Ni-based Amorphous alloys and their Nanocrystalline Structure Xiangcheng Sun1 and Tiemin Zhao2 1
Center for Materials for Information Technology, The University of Alabama, Tuscaloosa, Alabama, 35487-0209 2 Lab of RSA, Institute of Metal Research, CAS, Shenyang, P. R. China ABSTRACT A Ni-based amorphous alloy in Ni60Ti20Zr20 system was prepared by melting spinning. The glass transition temperature (Tg) was as high as about 760 K, the supercooled liquid region was quite wide, ∆Tx = 50 K (∆Tx= Tx-Tg, Tx crystallization temperature), and the reduced glass transition temperature (Tg/Tm) was 0.60. The amorphous alloys exhibited a high tensile strength (σf = 1015 MPa) at room temperature. The electrical conductivity obeyed a T1/2 law over the range of 15 K< T < 300 K, which can be explained by an electron-electron interaction model. After annealing the amorphous alloy into primary crystallization, a nanocomposites consisted of metastable Ti2Ni and Zr2Ni nanophases with size less than 15 nm embedded in the amorphous matrix was appeared. INTRODUCTION Binary alloys can be stabilized by adding a third element which has an atomic size different from the other two elements [1], and, if that element has a very low heat of mixing with one of the other elements. Ni-Ti [2], and Ni-Zr [3] binary alloy systems have been prepared by mechanically alloying (MA) over wide composition ranges due to the large negative heat of mixing. From the related studies [4, 5], one expects that if an appropriate amount of Zr was added into Ni-Ti or Ti was added into Ni-Zr binary alloys, the glass forming ability (GFA) both Ni-Ti and Ni-Zr may be greatly enhanced. As important engineering materials, a number of Ni-based amorphous ternary alloys had ever been produced in Ni-Fe-B [6], Ni-Si-P-B [7] and Zr-Ni-M (M=Pd, Au, Pt) [8, 9] by melting spinning. It is rather important for the future progress of bulk amorphous alloys to fabricate new Ni-based amorphous alloys that high glass forming ability (GFA), good mechanical properties and high corrosion resistance. On the other hand, it is also the aim of the present work to investigate the amorphization possibility and their corresponding mechanical and physical properties. From both fundamental and technological points of view, it will be useful to optimize the microstructure, and to develop economic bulk Ni-based amorphous alloys. EXPERIMENTAL 99.99% pure Ni, Zr, and Ti were melted and cast into ingots of nominal composition Ni60Ti20Zr20 by non-consumable arc melting under a highly pure argon atmosphere. Amorphous alloy ribbons (about 3 mm wide, 0.02 mm thick) were derived by melt spinning onto a copper wheel from the Ni60Ti20Zr20 ingots.
I10.4.2
The thermal properties were measured by differential scanning calorimetry (DSC, TA Instruments model) at a heating rate of 40 K/min. The values of the glass transition temperature Tg, the onset temperature for first crystallization peak Tx, were determined from the DSC curves with an accuracy of ±1 K.
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