Deformation behavior of Zr-based bulk nanocrystalline amorphous alloys Cang Fan, Chunfei Li, and Akihisa Inoue* Japan Science and Technology Corporation, Sendai 982-0807, Japan Volker Haas Institute for Solid State and Materials Research Dresden, Helmholtzstrasse 20, 01169 Dresden, Germany Received 9 August 1999; revised manuscript received 2 December 1999 Mechanical properties of bulk Zr 55 Ni 5 Cu 30 Al 10 metallic glass alloy and Zr 53 Ti 5 Ni 10 Cu 20 Al 12 nanocrystalline- amorphous alloy were measured by compression tests at room temperature. Although no distinct plastic deformation is recognized in the Zr 55 Ni 5 Cu 30 Al 10 metallic glass, the Zr 53 Ti 5 Ni 10 Cu 20 Al 12 as-quenched alloy exhibits significant plastic strain. Moreover, we found that both the strength and plastic strain increased significantly with increasing volume fraction of nanocrystals, and the plastic strain achieved a maximum in the early stage of nanocrystallization. High-resolution electron microscopy showed that nanocrystals with average grain sizes of about 2.0 and 2.5 nm were embedded in the amorphous matrix of the as-quenched bulk Zr 53 Ti 5 Ni 10 Cu 20 Al 12 alloy and the specimen with the maximum plastic strain, respectively. Melt-spun amorphous alloys are known to exhibit both high strength and good bending ductility. However, upon annealing-induced crystallization, both properties are gener- ally lost. 1 For the last decade of this century, with the devel- opment of techniques making nanostructured materials, a substantial increase in the strength has been observed in a number of nanocrystalline-amorphous alloys prepared by isothermal annealing, 2,3 especially in several bulk nanocrystalline-amorphous alloys. 4–7 However, with bulk nanocrystalline-amorphous alloys a decrease in ductility but with a concurrent increase in strength with increasing volume fraction of nanocrystals is observed. 5 This behavior was interpreted to be due to the supposed brittleness of the precipitated nanocrystals. In the present work we investigated the mechanical prop- erties measured by compression tests and the microstructures observed by optical and high-resolution electron microscopy in bulk Zr 53 Ti 5 Ni 10 Cu 20 Al 12 nanocrystalline-amorphous al- loy. In contrast to investigations reported hitherto, we found that the compressive plastic strain increased with increasing volume fraction of nanocrystals. Zr 53 Ti 5 Ni 10 Cu 20 Al 12 ingots were initially prepared by arc melting the mixtures of pure metals in a purified argon at- mosphere and cast into a copper mould in vacuum. The alloy crystallizes via precipitation of a metastable phase in the pri- mary crystallization step leading to nanoparticles embedded in an amorphous matrix. 7 For comparison, a Zr 55 Ni 5 Cu 30 Al 10 amorphous alloy, which shows the typical large glass- forming ability, 8 was also prepared. X-ray measurements were performed on as-cast specimens to check the amorphic- ity of the sample. The amorphous alloys were partially crys- tallized by isothermal annealing in the supercooled liquid region, and the volume fraction V f of nanocrystals was esti- mated by differential scanning calorimetry DSCi.e., V f proportional to the heat release upon partial crystallization. Microstructures of the specimens were examined by high- resolution electron microscopy HREMJEM-3000F, oper- ated at 300 kV. The mechanical properties were measured by compression tests using cylinders of 2.0 mm in diameter and 4.5 mm long at a strain rate of 4.410 -4 s -1 at room temperature. Young’s modulus was measured by a strain gauge. The shear bands of a sample strained to 0.6% com- pressive plastic strain were investigated by optical micros- copy OM. Figure 1 shows the compressive stress-strain curves: a for bulk Zr 55 Ni 5 Cu 30 Al 10 amorphous alloy; b, c, and d for as-quenched and exemplarily for the investigated an- RAPID COMMUNICATIONS PHYSICAL REVIEW B CONDENSED MATTER AND MATERIALS PHYSICS THIRD SERIES, VOLUME 61, NUMBER 6 1 FEBRUARY 2000-II RAPID COMMUNICATIONS Rapid Communications are intended for the accelerated publication of important new results and are therefore given priority treat- ment both in the editorial office and in production. A Rapid Communication in Physical Review B may be no longer than four printed pages and must be accompanied by an abstract. Page proofs are sent to authors. PRB 61 0163-1829/2000/616/37613/$15.00 R3761 ©2000 The American Physical Society