Microscale deformation behavior of amorphous/nanocrystalline multilayered pillars

Metallic glasses have recently been extended their research and application in micro-electro-mechanical systems (MEMS). However, the brittle nature of metallic glasses in the bulk and thin film forms inevitably imposes limitation. The current study applies the new idea to adopt a thin layer of nanocrystalline metal film beneath the brittle binary ZrCu thin film metallic glass (TFMG) layer. This metal film needs to be sufficiently strong in modulus and strength and needs to be deposited with the appropriate film orientation. The face-centered cubic Cu {111} film appears to be too soft, the body-centered cubic Mo {110} film behaves to be too brittle, but the hexagonal close-packed Zr {0001} film matches all above requirements. The shear bands initiated in the ZrCu thin film metallic glass layer can be absorbed and accommodated by the nanocrystalline Zr {0001} layer via the nano-twinning mechanism. The original brittle ZrCu TFMG, with the inclusion of a Zr layer beneath, can behave highly ductile with semi-uniform plastic deformation of 55%, even more ductile than most pure metals. The amorphous-crystalline interface exhibits good strain compatibility after appreciable plastic deformation. This finding can impose great impact on the TFMG/metal multilayer structures useful for MEMS design. (C) 2010 Elsevier B.V. All rights reserved.