Plastic deformation of freestanding thin films: Experiments and modeling

Experimental measurements and computational results for the evolution of plastic deformation in freestanding thin films are compared. In the experiments, the stress–strain response of two sets of Cu films is determined in the plane-strain bulge test. One set of samples consists of electroplated Cu films, while the other set is sputter-deposited. Unpassivated films, films passivated on one side and films passivated on both sides are considered. The calculations are carried out within a two-dimensional plane strain framework with the dislocations modeled as line singularities in an isotropic elastic solid. The film is modeled by a unit cell consisting of eight grains, each of which has three slip systems. The film is initially free of dislocations which then nucleate from a specified distribution of Frank–Read sources. The grain boundaries and any film-passivation layer interfaces are taken to be impenetrable to dislocations. Both the experiments and the computations show: (i) a flow strength for the passivated films that is greater than for the unpassivated films and (ii) hysteresis and a Bauschinger effect that increases with increasing pre-strain for passivated films, while for unpassivated films hysteresis and a Bauschinger effect are small or absent. Furthermore, the experimental measurements and computational results for the 0.2% offset yield strength stress, and the evolution of hysteresis and of the Bauschinger effect are in good quantitative agreement.

[1]  J. Chaboche,et al.  Dislocations and elastic anisotropy in heteroepitaxial metallic thin films , 2003 .

[2]  Xiangshan Chen,et al.  Plane-strain Bulge Test for Thin Films , 2005 .

[3]  van der Erik Giessen,et al.  Incorporating three-dimensional mechanisms into two-dimensional dislocation dynamics , 2004 .

[4]  D. Clarke,et al.  Size dependent hardness of silver single crystals , 1995 .

[5]  Amit Acharya,et al.  Lattice incompatibility and a gradient theory of crystal plasticity , 2000 .

[6]  Xi Chen,et al.  The Mechanical Properties of Electroplated Cu Thin Films Measured by means of the Bulge Test Technique , 2001 .

[7]  A. Needleman,et al.  Size effects in polycrystalline thin films analyzed by discrete dislocation plasticity , 2005 .

[8]  W. Nix,et al.  A microbeam bending method for studying stress–strain relations for metal thin films on silicon substrates , 2004 .

[9]  Norman A. Fleck,et al.  Boundary layers in constrained plastic flow: comparison of nonlocal and discrete dislocation plasticity , 2001 .

[10]  Eduard Arzt,et al.  Small-scale plasticity in thin Cu and Al films , 2003 .

[11]  van der Erik Giessen,et al.  A discrete dislocation analysis of bending , 1999 .

[12]  Morton E. Gurtin,et al.  A gradient theory of single-crystal viscoplasticity that accounts for geometrically necessary dislocations , 2002 .

[13]  A. Evans,et al.  Stress evolution in passivated thin films of Cu on silica substrates , 1998 .

[14]  J. Vlassak,et al.  The effects of passivation layer and film thickness on the mechanical behavior of freestanding electroplated Cu thin films with constant microstructure , 2004 .

[15]  O. Kraft,et al.  Deformation behavior of thin copper films on deformable substrates , 2001 .

[16]  A. Needleman,et al.  Plasticity size effects in tension and compression of single crystals , 2005 .

[17]  A. Needleman,et al.  Two hardening mechanisms in single crystal thin films studied by discrete dislocation plasticity , 2005 .

[18]  Joost J. Vlassak,et al.  Bauschinger effect in thin metal films , 2005 .

[19]  M. Saif,et al.  Strain gradient effect in nanoscale thin films , 2003 .

[20]  Norman A. Fleck,et al.  A reformulation of strain gradient plasticity , 2001 .

[21]  Julia R. Greer,et al.  Size dependence of mechanical properties of gold at the micron scale in the absence of strain gradients , 2005 .

[22]  M. Ashby,et al.  Strain gradient plasticity: Theory and experiment , 1994 .

[23]  J. R. Patel,et al.  X-ray microdiffraction: local stress distributions in polycrystalline and epitaxial thin films , 2004 .

[24]  Horacio Dante Espinosa,et al.  A methodology for determining mechanical properties of freestanding thin films and MEMS materials , 2003 .

[25]  Joost J. Vlassak,et al.  A new bulge test technique for the determination of Young’s modulus and Poisson’s ratio of thin films , 1992 .

[26]  고성현,et al.  Mechanism-based Strain Gradient Plasticity 를 이용한 나노 인덴테이션의 해석 , 2004 .

[27]  Lucia Nicola,et al.  Discrete dislocation analysis of size effects in thin films , 2003 .

[28]  K. Schwarz,et al.  Dislocation interactions in thin FCC metal films , 2003 .

[29]  Morton E. Gurtin,et al.  Effect of defect energy on strain-gradient predictions of confined single-crystal plasticity , 2005 .

[30]  N. M. Ghoniem *,et al.  Dislocation motion in anisotropic multilayer materials , 2005 .

[31]  W. Soboyejo,et al.  An investigation of the effects of thickness on mechanical properties of LIGA nickel MEMS structures , 2003 .

[32]  W. Soboyejo,et al.  A nano-indentation study on the plasticity length scale effects in LIGA Ni MEMS structures , 2003 .

[33]  Huajian Gao,et al.  Mechanism-based strain gradient plasticity— I. Theory , 1999 .

[34]  J. Vlassak,et al.  The mechanical properties of freestanding electroplated Cu thin films , 2006 .

[35]  Horacio Dante Espinosa,et al.  Plasticity size effects in free-standing submicron polycrystalline FCC films subjected to pure tension , 2004 .

[36]  Ladislas P. Kubin,et al.  Dislocation Microstructures and Plastic Flow: A 3D Simulation , 1992 .

[37]  Michael D. Uchic,et al.  Size-affected single-slip behavior of pure nickel microcrystals , 2005 .

[38]  van der Erik Giessen,et al.  Discrete dislocation plasticity: a simple planar model , 1995 .

[39]  Huajian Gao,et al.  Two-dimensional discrete dislocation models of deformation in polycrystalline thin metal films on substrates , 2005 .

[40]  Peter Gumbsch,et al.  Discrete dislocation simulation of plastic deformation in metal thin films , 2004 .

[41]  D. Dimiduk,et al.  Sample Dimensions Influence Strength and Crystal Plasticity , 2004, Science.

[42]  N. Fleck,et al.  Strain gradient plasticity , 1997 .

[43]  Anthony G. Evans,et al.  A microbend test method for measuring the plasticity length scale , 1998 .

[44]  van der Erik Giessen,et al.  Incorporating three-dimensional mechanisms into two-dimensional dislocation dynamics (vol 12, pg 159, 2004) Erratum , 2004 .