Preparation of a new Zr42Ti12Cu14Ni10Be20Mg1Y1 bulk amorphous alloy

Abstract

Since the discovery of the first amorphous phase in a Au-Si system by rapid solidification in 1960 [1], numerous metallic glasses have been found. They show various kinds of characteristics, such as good mechanical properties, unique physical and chemical properties. Amorphous metallic alloys have held the potential for a large variety of applications. All applications, however, have been limited by the thickness (<50 μm) of the amorphous alloys that could be prepared using techniques based on the rapid solidification of melts. Turnbull and collaborators utilized fluxing methods to suppress heterogeneous nucleation of crystals in the undercooled melt, and found that bulk amorphous phases could form in the absence of impurities [2]. However, such formation of amorphous phases required critical cooling rates as fast as 105–106 K/s to suppress crystallization and the dimension of the bulk samples was limited to be thin sheets or ribbons. One of the most important recent developments in materials synthesis is the discovery that a few metallic melts can be cast in bulk amorphous form at relatively slow cooling rates. In 1990, Inoue and his co-workers began to systematically investigate the glass-forming ability of a number of multi-component alloy families, including Ln-Al-TM, Zr-Al-TM, Hf-Al-TM and Ti-ZrTM systems (Ln= lanthanide metal, TM= transition metal). For such alloys, the critical cooling rates for glass formation range from 10 to 100 K/s [3]. Copper mold casting was used to prepare a large number of ternary and quaternary alloys with dimensions in the 1–10 mm range [4]. In 1991, Peker and Johnson started to investigate a number of Zr/Ti base alloys for bulk glass formation and obtained bulk amorphous alloys in Zr-Ti-Cu-Ni-Be, Zr-Ti-Ni-Cu and related systems at low critical cooling rates [2]. Recently, Fe-base bulk amorphous alloys were found to exhibit good soft magnetism, and hard magnetism, high magnetostriction in low applied magnetic fields [5–7]. Composites with a bulk metallic glass matrix were also synthesized [8]. In this communication, we report the synthesis of a new Zr/Mg base bulk amorphous alloy with large dimension at slow cooling rates. The alloy had a nominal composition of Zr42Ti12Cu14Ni10Be20Mg1Y1, and was prepared by arc melting under a Ti-gettered argon atmosphere. The ingots were re-melted in a silica tube and subsequently quenched in water to get cylindrical rods with a diameter of 7 mm. The weight of the sample was checked at various stages of processing. The weight loss of the sample after melting was less than 1%. The silica tube was evacuated by a high-vacuum instrument and filled with argon. The critical cooling rate (Rc) of the alloy was estimated to be about 16 K/s using a previous method [9]. Cylindrical bulk samples with a dimension of φ7 mm× 25 mm were examined by X-ray diffractometry. The thermal stability was evaluated by TA INSTRUMENT differential scanning calorimetry (DSC) at a heating rate of 10 K/min. Fig. 1 shows such a rod with a size of about φ7 mm× 10 mm. The bulk sample has a smooth outer surface and good metallic luster. The Vicker hardness was measured to be 514 Kg/mm2. Fig. 2 shows the differential scanning calorimetry (DSC) curve (at a heating rate 10 K/min) for the water quenched Zr42Ti12Cu14Ni10Be20Mg1Y1 alloy. It can be seen that an endothermic heat anomaly characteristic of the glass transition begins at 583 K. At higher temperatures, two crystallization peaks show up. The quenched Zr42Ti12Cu14Ni10Be20Mg1Y1 amorphous alloy exhibits the progress of the glass transition, followed by the appearance of a wide supercooled liquid region and crystallization. The supercooled liquid