Glass formation in the NiCrNb system

Abstract

The development of metallic glasses which can be produced by rapid-quenching techniques has led to a new class of materials with extraordinary properties [1]. Depending upon the alloy composition, metallic glasses have been found to exhibit any of several attractive properties, such as good corrosion resistance, stability under irradiation, high strength and hardness and interesting magnetic and electrical properties. Many of the metallic glasses studied so far crystallize at relatively low temperatures and structural relaxation of the glass may occur as much as 200 K below the crystallization temperature leading to further deterioration in thermal stability. It is therefore desirable to identify glasses of higher crystallization temperature. Some effort has been made in this direction to develop metal-metalloid glasses [2], but little attention has been paid to glasses containing only metallic elements. Of the known metal-metal glass-forming alloys, the Ni60Nb40 (subscripts refer to at %) composition readily forms a glass of high crystallization temperature (Tx~923K) [3-6]. Since the addition of chromium ha's been found to be most effective in improving corrosion resistance in metalmetalloid glasses [1], we have investigated the effect of its addition on the glass-forming ability of Ni60Nb40 alloys. Alloy buttons of compositions Ni60CrxNb40 x and Ni60 yCryNb40 (x, y = 0, 5, 10, 13 and 15) were made by arc melting high-purity components in a pure argon atmosphere over a water-cooled copper crucible. The buttons were remelted at least six times to ensure homogeneity. Weight losses during melting were negligible and the nominal compositions were accepted. Rapidly quenched ribbons were prepared in s i tu by the melt-spinning technique. After induction melting in a quartz nozzle of around 1 mm orifice diameter, the molten metal was ejected onto a rotating polished copper wheel (~ 200mm diameter) using an ejection pressure of pure argon. Before melting, the nozzle containing the alloy pieces was repeatedly flushed with argon and an additional argon flow around the nozzle was maintained throughout the experiment by incorporating a concentric quartz tube of larger diameter to prevent oxidation of the melt pool. The ejection pressure and wheel velocity were adjusted to provide around 20 to 25 #m thick and 2 to 3 mm wide ribbons. X-ray-diffraction analyses of the asquenched ribbons were made using a Philips diffractometer with CoK~ radiation at a scanning rate of 1 ° (20)min -j . X-ray-diffractometer traces of the asquenched alloy ribbons are shown in Fig. 1. In the melt-spun Ni60CrxNb40 x alloy ribbons, X-ray diffraction revealed only diffuse intensity maxima characteristics of an amorphous