Bulk titanium-rich alloys containing nanoscale disordered regions
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INTRODUCTION
IT is well known that amorphous materials can have a significant impact on technology if they can be fabricated in bulk form. However, amorphous alloys prepared by present methods, such as sputtering, vapor deposition, melt spinning, mechanical alloying, etc., are generally in the form of ribbons or particles. Although these ribbons or particles can be consolidated into bulk form, this is not an ideal way to prepare amorphous bulk materials due to resulting interfaces, porosity, and possible crystallization in the consolidated bulk. Some special methods have been introduced that can fabricate amorphous bulk materials with diameters of a few millimeters, including containerless solidification of alloys in a drop-tube,[1] pressure quenching,[2] and fluxing.[3] Recently, researchers have focused on looking for easy glass forming alloys in which an amorphous phase can be obtained at a slow cooling rate from the melt. They succeeded in the following alloy systems: Al-TM-RE ternary[4,5] (where TM 5 transition metals, RE 5 rare earths, and Y, Zr, Hf, or Rh), Mg-based,[6] Zr-based (Zr-Ni-CuAl[7] and Zr-Ti-Cu-Ni-Be[8]), Ti(34.4 pct)-Zr-Ni-Cu,[9] and Pd-based (Pd-Ni-P[10] and Pd-Cu-Ni-P[11]). This realization of bulk vitrification via melt quenching in a diverse group of alloys, without employing special techniques, gives the new promise of creating large-scale amorphous materials. Meanwhile, there have been a few reports concerning ‘‘spontaneous vitrification’’ of a metastable crystalline phase in rapidly quenched Ti60Cr40 alloys during subsequent annealing at around 600 7C.[12] However, later studies, including those performed by our group, have been unable to DONGJIAN LI, Research Associate, and S.J. POON, Professor, Department of Physics, and K.J. DOHERTY, Graduate Research Assistant, and G.J. SHIFLET, Professor, Department of Materials Science and Engineering, are with the University of Virginia, Charlottesville, VA 22903. This article is based on a presentation made in the ‘‘Structure and Properties of Bulk Amorphous Alloys’’ Symposium as part of the 1997 Annual Meeting of TMS at Orlando, Florida, February 10–11, 1997, under the auspices of the TMS-EMPMD/SMD Alloy Phases and MDMD Solidification Committees, the ASM-MSD Thermodynamics and Phase Equilibria, and Atomic Transport Committees, and sponsorship by the Lawrence Livermore National Laboratory and the Los Alamos National Laboratory. METALLURGICAL AND MATERIALS TRANSACTIONS A
repeat this work.[13–18] In most cases, not even partial amorphization could be detected. Ohsaka et al.[17] stated that spontaneous vitrification of undistorted b in Ti60Cr40 is not feasible because the free energy of the b phase is lower than that of the amorphous phase at 600 7C. Despite the failure in repeating the amorphization of metastable phases solely through annealing in all of the systems that Blatter et al.[12] reported, the idea of spontaneous vitrification is still very attractive. If spontaneous vitrification from the solid state can be accomplished, it provides
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