Progress in Consolidation of Amorphous Zr-based Powder into Bulk Metallic Glass
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CC3.5.1
Progress in Consolidation of Amorphous Zr-based Powder into Bulk Metallic Glass Suveen N. Mathaudhu1, Jae Taek Im1, Robert E. Barber1, Iver E.Anderson2, Ibrahim Karaman1 and K.Ted Hartwig1 1 Texas A&M University, Dept. of Mechanical Engineering, College Station, TX 77843-3123, U.S.A. 2 Ames Laboratory, Iowa State University, Ames, IA 50011, U.S.A. ABSTRACT Equal channel angular extrusion (ECAE) is used to consolidate amorphous Vitreloy 106a (Zr58.5Nb2.8Cu15.6Ni12.8Al10.3) powder into bulk metallic glass. Consolidations are performed on gas atomized powder containing 1280 ppmw oxygen encapsulated in copper cans and 780 ppmw oxygen powder encapsulated in nickel cans in a 90° die-angle tool at temperatures above the glass transition temperature (Tg) but below the rapid crystallization temperature (Tx), in the supercooled liquid region (∆T). Results show that V106a is successfully consolidated to nominal full density after one extrusion pass. Good particle-to-particle bonding and significant particle deformation are observed in the consolidated alloy. A lower oxygen content is beneficial due to the larger undercooled region and the additional time for processing. The low oxygen content material shows little change in thermal stability after being consolidated when compared to the original powder but fine interparticle cracks are observed in some of the consolidates. ECAE appears to be a viable method for consolidating amorphous metal powders into bulk amorphous metal. INTRODUCTION The production of bulk metallic glasses (BMG) has attracted much attention due to their high tensile strength and hardness [1-4] and resistance to both corrosion and wear [5]. These properties make BMGs attractive for structural applications. Most BMGs have been produced by rapid cooling from the melt (vacuum casting), but due to critical cooling rate requirements, material thickness is limited [6]. Two main powder consolidation techniques, conventional area reduction extrusion [7-10] and hot isostatic pressing (HIPing) [11-13], have been used to produce BMGs. HIPing is limited in its ability to achieve adequate particle-to-particle bonding and by long cycle times at high temperatures. Area reduction extrusion is limited by the resulting smaller cross section of the product. Equal channel angular extrusion (ECAE) is a potential powder consolidation method that overcomes some of the difficulties associated with HIPing and conventional extrusion. The ECAE technique involves subjecting the powder to simple shear in a die containing intersecting channels (figure 1) [14-16]. Potential benefits of the ECAE process are: constant workpiece cross-section, uniform deformation throughout workpiece and consolidation to near full density after a single extrusion [17].
CC3.5.2
~80% density Fully Dense
Shear Zone
Figure 1. Two-dimensional schematic of ECAE powder consolidation. Successful ECAE consolidations have been performed on several powders including 6061 Al, WC+Co, and Cu+Ag [17, 18]. Work has also been done on the consolidation of powde
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