A new approach to preparing three-dimensional amorphous alloys

Abstract

Considerable interest has been evident in preparing three-dimensional amorphous alloys for the past decade because the traditional rapid-quenching technique is applicable only to the production of very thin ribbon, strip and powder, of which the practical use is generally limited in the scope of electronics and power industry. Currently the preparation of three-dimensional amorphous alloys can be divided into two types of methods: solid-state synthesis and denucleation of liquid alloys. The former method, which has been increasingly developed in some countries such as the FRG and Japan, consists of solid-state reactions and powder consolidation. Amorphous Ni6sZr32 wire of 1 mm diameter has been produced by solid-state reactions from as-deformed composite under isothermal conditions (300 °C for 100 h) [1]. Power consolidation techniques including explosive compaction [2], warm extrusion [3] and high-temperature sintering [4] have been utilized to prepare bulk amorphous samples with rotational symmetry, such as rods, tubes or cones. Some key problems such as cracks and non-uniform properties of synthesized specimens by the above-mentioned technique are expected to be solved in spite of results attained recently. In 1984 an exciting achievement was made by Kui et al. [5], who succeeded in undercooling bulk Pd40Ni40P20 alloy to glassy spheroids of diameter 10 mm by fluxing. This confirms that the denucleation technique in which heterogeneous nuclei are removed leads to the formation of bulk metallic glasses at much lower cooling rates. However, the formation of bulk glass is possible only if the homogeneous nucleation frequency of the melt is sufficiently low and if the heterogenous nucleation centres are thoroughly eliminated. Obviously, most practical alloys, for which the,' lowest temperatures of crystal nucleation onset are above their glass transition temperatures (Tg) in the slow-cooling environment, can hardly meet these strict conditions. Therefore, rapid quenching is indispensable to trap the liquid alloys into three-dimensional metallic glasses. In this letter a new method of preparing three-dimensional amorphous alloys by a rapid-quenching denucleated melt (RQDM) is put forward. The RQDM experiment was composed of two steps: denucleating liquid alloys until a high undercooling is attained and rapid quenching the denucleated liquid alloys. The experiments were performed in a vacuum of < 2.7 x 10 .3 Pa on our self-made high-frequency electromagnetic levitation melter and hammer-and-anvil apparatus as shown in Fig. 1.