薄膜与小尺度材料及力学性能研究组

Mechanics of nanoscale metallic multilayers: from atomic-scale to micro-scale

J. Wang^a, R.G. Hoagland^a and A. Misra^b

Received 30 September 2008; revised 15 November 2008; accepted 18 November 2008. Available online 7 December 2008.

Transmission electron microscopy investigation of the atomic structure of interfaces in nanoscale Cu-Nb multilayers

K. Yu-Zhang ^a;  J. D. Embury ^b;  K. Han ^c; A. Misra ^d

^a Dpartement de Physique, Laboratoire de Microscopies et d'Etude de Nanostructures, Universit de Reims, Reims Cedex 02, France

^b Department of Materials Science and Engineering, McMaster University, Hamilton, Canada

^c National High Magnetic Field Laboratory/Florida State University, Tallahassee, USA

^d Los Alamos National Laboratory, Los Alamos, NM 87545, USA

Abstract

Multilayers of Cu-Nb have been grown on a Nb seed layer on a Si (100) substrate using a magnetron sputtering technique. The bilayer period (Λ) was varied from 10 to 2.4 nm. Cross-sectional transmission electron microscopy (XTEM) and high-resolution TEM (HRTEM) were used to study the detailed structure as a function of the bilayer period. Although the majority of the structures conformed to a Kurdjumov-Sachs (K-S) orientation relationship between the Cu and Nb layers, the structures exhibit considerable spatial variation. In some local regions, a Nishiyama-Wasserman (N-W) orientation relationship was found. In addition, considerable distortions were observed in both the Cu and Nb regions close to the interface. Using both HRTEM imaging and fast Fourier transform (FFT) of HRTEM images, early stage of the fcc to bcc transition in Cu was detected. The results suggest that, in multilayer structures, the detailed structure of the interface and large local distortions may play an important role in interface-controlled plasticity.

Keywords: multilayer; CulNb; deformation; nanostructure; lattice distortion; orientation relationship

Atomistic modeling of the interaction of glide dislocations with “weak” interfaces

J. Wang^a, R.G. Hoagland^a, J.P. Hirth^b and A. Misra^b

^aMaterials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

^bCenter for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA

Received 1 July 2008; revised 26 July 2008; accepted 26 July 2008. Available online 25 August 2008.

Abstract

Using atomistic modeling and anisotropic elastic theory, the interaction of glide dislocations with interfaces in a model Cu–Nb system was explored. The incoherent Cu–Nb interfaces have relatively low shear strength and are referred to as “weak” interfaces. This work shows that such interfaces are very strong traps for glide dislocations and, thus, effective barriers for slip transmission. The key aspects of the glide dislocation–interface interactions are as follows. (i) The weak interface is readily sheared under the stress field of an impinging glide dislocation. (ii) The sheared interface generates an attractive force on the glide dislocation, leading to the absorption of dislocation in the interface. (iii) Upon entering the interface, the glide dislocation core readily spreads into an intricate pattern within the interface. Consequently, the glide dislocations in both Cu and Nb crystals are energetically favored to enter the interface when they are located within 1.5 nm from the interface. In addition to the trapping of dislocations in weak interfaces, this paper also discusses geometric factors such as the crystallographic discontinuity of slip systems across the Cu/Nb interfaces, which contribute to the difficulty of dislocation transmission across an interface. The implications of these findings to the unusually high strengths experimentally measured in Cu/Nb nanolayered composites are discussed.

Keywords: Molecular dynamics; Dislocation; Interfaces; Multilayers; Slip transmission

1.Interface and surface effects on ferroelectric nano-thin films
Pages 2966-2974
L. Hong, A.K. Soh, Y.C. Song and L.C. Lim

2.Dislocation structures and their relationship to strength in deformed nickel microcrystals
Pages 2988-3001
D.M. Norfleet, D.M. Dimiduk, S.J. Polasik, M.D. Uchic and M.J. Mills

3.Atomistic simulations of the shear strength and sliding mechanisms of copper–niobium interfaces
Pages 3109-3119
J. Wang, R.G. Hoagland, J.P. Hirth and A. Misra

Deformability of ultrahigh strength 5  nm Cu/Nb nanolayered composites

N. A. Mara,¹ D. Bhattacharyya,² P. Dickerson,¹ R. G. Hoagland,¹ and A. Misra²

¹Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

²Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA

Thermal stability of sputtered Cu films with nanoscale growth twins

O. Anderoglu,¹ A. Misra,² H. Wang,³ and X. Zhang¹

¹Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123, USA

²Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Mailstop G755, Los Alamos, New Mexico 87545, USA

³Department of Electrical Engineering, Texas A&M University, College Station, Texas 77843-3128, USA

We have investigated the thermal stability of sputter-deposited Cu thin films with a high density of nanoscale growth twins by using high-vacuum annealing up to 800 °C for 1 h. Average twin lamella thickness gradually increased from approximately 4 nm for as-deposited films to slightly less than 20 nm after annealing at 800 °C. The average columnar grain size, on the other hand, rapidly increased from approximately 50 to 500 nm. In spite of an order of magnitude increase in grain size, the annealed films retained a high hardness of 2.2 GPa, reduced from 3.5 GPa in the as-deposited state. The high hardness of the annealed films is interpreted in terms of the thermally stable nanotwinned structures. This study shows that nanostructures with a layered arrangement of low-angle coherent twin boundaries may exhibit better thermal stability than monolithic nanocrystals with high-angle grain boundaries. ©2008 American Institute of Physics 

The multiscale modeling of plastic deformation in metallic nanolayered composites

A. Misra¹, M. J. Demkowicz¹, J. Wang¹ and R. G. Hoagland¹