Preparation and Properties of Ti 50 Cu 28 Ni 15 Sn 7 Bulk Metallic Glass by Vacuum Hot Pressing
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INTRODUCTION
BULK amorphous alloys with a wide supercooled liquid region have been prepared successfully in Zr-, Ln, Fe-, Co-, Ni-, Cu-, Pd-, and Mg-based alloy systems.[1] The supercooled liquid region (DT) is defined by the temperature difference between the glass transition temperature (Tg) and crystallization temperature (Tx); i.e., DT = Tx – Tg. The increase of DT indicates that the thermal stability of the supercooled liquid state improves against crystallization, and, thus, the bulk amorphous alloys can be prepared at a relative low cooling rate by the conventional casting process. For instance, Zr-based bulk amorphous alloys are excellent advanced engineering materials and have been applied to make components of sporting goods, optical instruments, and writing implements;[2] while bulk amorphous Ti50Ni15Cu25Sn5Zr5 alloys are expected to exhibit high tensile strength and relatively high corrosion resistance at room temperature.[3] The Ti-based bulk amorphous alloy systems have attracted R & D interest due to their relatively low H.M. LIN, Professor, is with the Department of Materials Engineering, Tatung University, Taipei, Taiwan, R.O.C. C.K. LIN, Professor, is with the Department of Materials Science and Engineering, Feng-Chia University, Taichung, Taiwan, R.O.C. R.R. JENG, Deputy Director, and H.Y. BOR, Chief, Metallurgy Section, are with the Materials & Electro-Optics Research Division, Chung-Shan Institute of Science & Technology, Tao-Yuan, Taiwan, R.O.C. P.Y. LEE, Professor, is with the Institute of Materials Engineering, National Taiwan Ocean University, Keelung, Taiwan, R.O.C. Contact e-mail: [email protected] This article is based on a presentation given in the symposium entitled ‘‘Bulk Metallic Glasses IV,’’ which occurred February 25– March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee. Article published online September 26, 2007 METALLURGICAL AND MATERIALS TRANSACTIONS A
density or high specific strength. The Ti-based amorphous alloy systems including Ti-Ni-Cu,[4] Ti-Ni-Cu-Al,[5] Ti-Zr-Ni-Cu-Al,[6] Ti-Ni-Cu-Sn,[7,8] Ti-Ni-Cu-Si-B,[9] etc. have been investigated. However, due to the highly reactive nature of Ti, it is difficult to prepare Ti-based bulk metallic glasses (BMGs) by conventional mold casting methods. The thickness of Ti-based BMGs is only several millimeters, much smaller than those of other BMG systems.[10] Numerous R & D efforts to prepare amorphous alloys have focused on the different implementations of the rapid solidification and solid-state reaction.[11] For instance, mechanical alloying (MA), a relatively simple technique to prepare amorphous alloy powders via a solid-state reaction, have been used.[12,13] The asmilled powders are suitable for further processing, such as consolidating at a temperature within the supercooled liquid region to prepare corresponding BMG. For instance, Zhang et al.[14] have reported that ball-milled Ti50Cu18Ni22Al4Sn6 amorphous powders can be consolidated into BM
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