Effect of multilayer interface through in situ fracture of Cu/Nb and Al/Nb metallic multilayers
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FOCUS ISSUE
PLASTICITY AND FRACTURE AT THE NANOSCALES
Effect of multilayer interface through in situ fracture of Cu/ Nb and Al/Nb metallic multilayers Hashina Parveen Anwar Ali1
, Ihor Radchenko1, Nan Li2, Arief Budiman1,a)
1
Xtreme Materials Lab, Engineering Product Development (EPD) Pillar, Singapore University of Technology & Design (SUTD), Singapore 487372, Singapore 2 Center for Integrated Nanotechnologies (CINT), Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA a) Address all correspondence to this author. e-mail: [email protected] Received: 29 September 2018; accepted: 12 November 2018
Interfaces can influence the mechanical properties of metallic multilayers, even between different combinations of face-centered cubic (FCC)/body-centered cubic (BCC) constituents, as reported from many experiments. Recent literature has shown promise for fracture being delayed or even stopped at these interfaces. However, no studies have investigated the influence of their constituents on the subsequent mechanisms of fracture leading to failure. We performed in situ microfracture bending tests of the notched clamped beams made from physical vapor deposited Cu/Nb and Al/Nb multilayers. A catastrophic, linear elastic, brittle fracture was observed for the Cu/Nb beams, whereas a more delayed fracture with a gradual crack propagation was observed for the Al/Nb beams. These observations reveal differences in mechanisms because of the FCC element, interface/boundary blocking of dislocation motion, and effect of grain boundaries in the multilayers. Through this study, FCC/BCC metallic multilayers can be designed with enhanced fracture resistance and mechanical strength.
Introduction Metallic multilayers have fascinated researchers with their extraordinary mechanical properties by controlling its layer thickness, the number of constituents, and the type of materials from metal–metal [1, 2] to metal–ceramics [3, 4] and recently metal–graphene [5, 6]. These combinations have resulted in enhanced mechanical properties such as ultrahigh strength [7], thermal stability [8, 9, 10], resistance to radiation extremes [11, 12], and linear resistivity versus strain relationship [13]. These properties have been associated with the dislocation strengthening mechanisms [14] that occur at the interface of multilayers at different length scales. In this paper, we will be focusing on the metal–metal multilayers of Al/Nb and Cu/Nb with the face-centered cubic (FCC)/body-centered cubic (BCC) interface. The FCC/BCC interface can have a range of coherency depending on the lattice mismatch of the two constituents. The strain due to incoherency is partially relieved by misfit dislocations with the residual compressive strain present in the film. Al/Nb multilayers have a coherent interface with
ª Materials Research Society 2019
a very low lattice mismatch of 0.4% because of their close match in their interplanar spacings of Al(111) (do 5 0.234 nm) and Nb(110) (do 5 0.233 nm). They
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