Deformation-induced structural transformation leading to compressive plasticity in Zr 65 Al 7.5 Ni 10 Cu 12.5 M 5 (M = N
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Hidemi Kato Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
Mitsuhide Matsushita Advanced Technology Division, JEOL Ltd., Tokyo 196-8558, Japan
Akihisa Inoue World Premier International (WPI)–Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan (Received 4 November 2009; accepted 1 March 2010)
Zr65Al7.5Ni10Cu12.5Nb5 glass was found to exhibit a large plastic compressive strain of over 10% and the property was suggested to be due to deformation-induced nanocrystallization. A transmission electron microscopic observation, however, only revealed obscure ordered clusters with a size of 2 nm in the fracture surface of a deformed sample, instead of well-identified crystals as previously reported for the Zr–Al– Ni–Cu–Pd system. This phenomenon is suggested to correlate with the higher viscosity of supercooled liquid and the slower grain growth of icosahedral phase during primary crystallization in the Zr65Al7.5Ni10Cu12.5Nb5 compared to those in the Zr65Al7.5Ni10Cu12.5Pd5 alloy. The role of the deformation-induced nanoclusters on the enhanced compressive plasticity was discussed.
I. INTRODUCTION
Attractive mechanical properties, such as high strength approaching the theoretical strength, high elastic energy storage per unit volume, high hardness, low mechanical damping, and high fracture toughness have made bulk glassy alloys (BGAs) to be considered as exceptional structural materials.1,2 These materials, however, exhibit limited room-temperature plasticity in most cases. A significant plasticity can be obtained by modifying or introducing new phases into the initial glassy structure. Deformation-induced nanocrystallization is a phenomenon in which a secondary phase with nanoscale size is precipitated dynamically during deformation within the initial glassy phase. The existence of nanocrystals in the glassy phase restricts the rapid propagation of shear bands and prevents the catastrophic failure leading to global ductility. This phenomenon had been extensively studied and reported in various works.3–12 One of the evidences of deformation-induced nanocrystallization in a metallic glass was revealed in the Zr65Al7.5Ni10Pd17.5 alloy3 by direct observation on the fracture surface of a deformed sample using transmission electron microscopy (TEM). The investigation on the mechanical a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0153 J. Mater. Res., Vol. 25, No. 6, Jun 2010
properties concerning this deformation phenomenon was then extended for various compositions in the Zr65Al7.5Ni10Cu17.5–xPdx (x ¼ 1–17.5 at.%) glassy alloy system,10,11 as well as compared with another system,12 and used for mechanical property improvement.11 It was found that Pd-containing alloys of x ¼ 5–17.5 at.% exhibited significant room-temperature plasticity of 5% to 7% following the mechanism of deformation-induced nanocrystallization. The origin of the deformation-induced nanocrystallization in the Zr65Al7.5Ni10Cu17.5–xPdx system
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