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Ductile to brittle transition in the $Zr_4_1_._2Ti_1_3_._7_5Cu_1_2_._5Ni_1_0Be_2_2_._5$ bulk metallic glass

Raghavan, R and Murali, p and Ramamurty, U (2006) Ductile to brittle transition in the $Zr_4_1_._2Ti_1_3_._7_5Cu_1_2_._5Ni_1_0Be_2_2_._5$ bulk metallic glass. In: Intermetallics, 14 (8-9). pp. 1051-1054.

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Abstract

The variation of impact toughness, \Gamma, of a $Zr_4_1_._2Ti_1_3_._7_5Cu_1_2_._5Ni_1_0Be_2_2_._5$ (Vitreloy-1) bulk metallic glass (BMG) within the temperature range of 123–423 K was evaluated by using an instrumented Charpy impact testing machine, in order to examine if the BMGs exhibit ductile-to-brittle transition (DBT) that is seen in rapidly quenched glasses. Results show an abrupt reduction in \Gamma when the testing temperature is lowered to below 150 K, implying that the BMGs are also prone to the DBT. Fractographic observations indicate a transition in the fracture mode; from ductile vein-like morphology above DBT to a cleavage-dominant fracture mode below it. Complimentary Vickers indentation measurements show no variation in hardness with temperature. However, the shear banded plastic regions that are typically seen around the indents were observed to be completely absent around the indents that were made at low temperatures, indicating that the inhomogeneous plasticity mediated by shear bands becomes inoperative below a critical temperature resulting in the DBT. This observation suggests that the minimum amount of free volume required for extensive plasticity (and hence high toughness) in metallic glasses is strongly dependent on the temperature. Testing of the structurally relaxed samples (through annealing at 530 K for 2.5 h that induces severe embrittlement at room temperature) at 423 K reveal almost complete recovery of \Gamma, supporting this hypothesis.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to Elsevier.
Keywords: B. Brittleness and ductility;B. Glasses, metallic;F. Mechanical testing
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 17 Jun 2006
Last Modified: 19 Sep 2010 04:29
URI: http://eprints.iisc.ernet.in/id/eprint/7669

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