New Glassy Zr-Al-Fe and Zr-Al-Co Alloys with a Large Supercooled Liquid Region

Abstract

New Zr-Al-Co and Zr-Al-Fe ternary glassy alloys were found to exhibit a large supercooled liquid region above 50 K before crystal- lization. The largest value of the supercooled liquid region was 64 K for Zr 55Al20Co25 and 50 K for Zr70Al15Fe15. The highest value of the reduced glass transition temperature (Tg/Tl) was 0.61 for Zr55Al20Co25 and 0.60 for Zr70Al15Fe15. The use of the Zr55Al20Co25 alloy with the highest Tg/Tl has enabled us to form bulk glassy alloy rods with diameters up to 3 mm by copper mold casting. The Young's modulus, yield strength, compressive fracture strength, elastic elongation and fracture elongation of the Zr 55Al20Co25 glassy rod are 92 GPa, 2050 MPa, 2200 MPa, 2.1% and 0.9%, respectively. The distinct plastic elongation indicates that the Zr-based bulk glassy alloy has rather a good ductile nature. The synthesis of the high-strength bulk glassy alloy in the new ternary system is expected to gain a new application field as a new type of bulk glassy alloy. For the last decade, much attention has been paid to bulk glassy alloys because of the importance of scientific and engi- neering aspects. The motivation for the present global atten- tion to bulk glassy alloys has been attributed to the discoveries of new series of glassy alloys with a large supercooled liquid region before crystallization in Mg-Ln(lanthanide metal)- (Ni, Cu), 1) Ln-Al-(Ni, Cu) 2) and Zr-Al-(Ni, Cu) 3) systems. The high thermal stability of the supercooled liquid against crystallization has enabled us to form bulk glassy alloys by various casting processes. It has subsequently been reported that bulk glassy alloys are also formed in a number of alloy systems, i.e., other Zr-based systems of Zr-Ti-Be-(Ni, Cu) 4) and Zr-(Ti, Nb, Pd)-Al-(Ni, Cu), 5) and Ti-, 6) Hf-, 7) Fe-, 8) Pd-Cu-, 9) Co-, 10) Ni- 11) and Cu- 12) based systems. The low- est critical cooling rate for glass formation is 0.03 K/s for the Pd-Cu-Ni-P system. The maximum sample diameter is ap- proximately 80 mm for the Pd-based system 13) and 30 mm for the Zr-based system. 14) The Zr- and Pd-based bulk glassy al- loys have been used as practical materials of sporting goods and electrodes. 15-17) In the development history of the Zr- based bulk glassy alloys, their alloy components had been limited to two groups of Zr-Al-(Ni, Cu) including Ti, Nb, Ta or Pd and Zr-Ti-Be-(Ni, Cu). It is important to search for new Zr-based glassy alloys with the high thermal stability of supercooled liquid and to extend bulk glassy alloy systems. Very recently, we have found that a large supercooled liquid region above 50 K before crystallization is obtained for new glassy alloys in Zr-Al-Fe and Zr-Al-Co systems. The find- ing of the simple ternary glassy alloys is important because the extension of the ternary base system to more multicom- ponent systems is expected to form bulk glassy alloys with a larger supercooled liquid region and higher glass-forming ability. This paper presents the composition ranges in which glassy alloys with a larger supercooled liquid region before crystallization are formed in Zr-Al-Fe and Zr-Al-Co ternary systems. Further, thermal and mechanical properties of their glassy alloys are investigated. 2. Experimental Procedure