Glass Forming Ability and Crystallization Behaviors of the Ti-Cu-Ni-(Sn) Alloys with Large Supercooled Liquid Region
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Glass Forming Ability and Crystallization Behaviors of the Ti-Cu-Ni-(Sn) Alloys with Large Supercooled Liquid Region Y.C. Kim, S. Yi, W.T. Kim1, D.H. Kim Center for Noncrystalline Materials, Dept. of Metallurgical Eng., Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749 Korea 1 Center for Noncrystalline Materials, Dept. of Physics, Chongju University 36 Naedok Dong, Chongju, Chungbuk, 360-764 Korea ABSTRACT The thermal stability and crystallization behavior of melt spun amorphous Ti50Cu35Ni15-xSnx (x=0, 3, 5, 7) alloys has been studied in by thermal analysis (DSC and DTA) and X-ray diffractometry. Partial replacement of Ni by Sn up to 5 at % in Ti50Cu35Ni15 alloy improved thermal stability and glass forming ability. The onset temperature of the first exotherm increased from 739 to 756 K with increasing Sn content x from 0 to 5, and then decreased to 745 K for the alloy with x=7 due to change in crystallization sequence. Melt spun amorphous Ti50Cu35Ni12Sn3 and Ti50Cu35Ni10Sn5 alloys exhibit 7x exceeding 78 and 76 K, respectively, which is significantly larger than 7x of 46 K in Ti50Cu35Ni15 alloy. Amorphous Ti50Cu35Ni15 alloy crystallized by precipitation of supersaturated cubic Ti(Ni,Cu) phase followed by decomposition into a mixture of TiCu and TiNi at higher temperature. Amorphous Ti50Cu35Ni15-xSnx (x=3, 5) phase crystallized by precipitation of cubic Ti(Ni,Cu) phase, followed by transformation into a mixture of TiNi, TiCu, Ti3Sn phases. Amorphous Ti50Cu32Ni8Sn7 phase crystallized by coprecipitation of cubic Ti(Ni,Cu) phase and unidentified phase, followed by transformation into a mixture of TiNi, TiCu, Ti3Sn phases.
INTRODUCTION Ti-based amorphous alloys are of scientific and commercial interest due to their high specific strength. Development of a Ti-based bulk amorphous alloy with a lower density and higher specific strength is expected to cause a further extension of application fields for bulk amorphous alloys. Ti based amorphous phase have been produced in several alloy systems such as Ti-Be-Zr [1], Ti-Ni-Si [2], Ti-Nb-Si-B [3], Ti-Ni-Cu [4], Ti-Ni-Cu-Al [5] and Ti-Zr-Ni-Cu-Al [6]. However the amorphous phase did not show clear glass transition to supercooled liquid state before crystallization during heating. Glass forming ability (GFA) of the alloys is poor and fully amorphous structure is available in only rapidly solidified samples. For Ti based bulk amorphous formation, enhancement of GFA is required. The GFA of alloys is often estimated by temperature range of supercooled liquid region, 7x = Tx – Tg, where Tx and Tg are onset temperature of crystallization and glass transition temperature, respectively. Recently, Ti alloys exhibiting wide 7x was observed in melt spun Ti-Cu-Ni amorphous alloys [7, 8, 9]. The Ti-Cu-Ni alloy system meets the requirements of the empirical rules for bulk metallic glass formation. Ti50Cu25Ni25 alloy has been found to show wide supercooled liquid region of about 40 K [7]. Further extension of the supercooled liquid region was achieved by partial replacement o
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