Mechanical Behavior at the Nanoscale VI: Thin Films and Multilayers
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Computational Materials Science and Engineering Committee, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Matthew Daly, University of Illinois-Chicago; Douglas Stauffer, Bruker Nano Surfaces & Metrology; Wei Gao, University of Texas at San Antonio; Changhong Cao, McGill University; Mohsen Asle Zaeem, Colorado School of Mines

Thursday 8:30 AM
March 3, 2022
Room: 262B
Location: Anaheim Convention Center

Session Chair: Matthew Daly, University of Illinois at Chicago; Megan Cordill, Erich Schmid Institute

8:30 AM  Invited
The Role of Thin Film Architecture to Enhance Fracture Resistance: Megan Cordill¹; ¹Erich Schmid Institute of Materials Science
    Multilayers on polymer substrates are of interest for several technical applications. The true understanding of how one layer affects the other during mechanical loading is still unknown. Therefore, single and bilayer thin films of Al and Mo were sputter deposited onto polyimide and biaxially strained in-situ with X-ray diffraction. The technique allows for the simultaneous measurement of lattice strains of Al and Mo to correlate the observed mechanical behavior of both materials. Using the evaluated film stress and FWHM evolutions, four domains of mechanical behavior are identified. The presence of the domains depends on the thickness of the Al films and, more importantly, the bilayer architecture. The maximum stress achieved in the Mo layers was also found to highly depend on the architecture and depend less on the Al film thickness. Results will demonstrate that the film architecture is more important than the film thickness to enhance fracture resistance.

9:00 AM
Investigating Role of Interfaces on Deformation Behavior of Metallic Nanolaminates Using Dislocation Dynamics Simulations: Aritra Chakraborty¹; Abigail Hunter¹; Laurent Capolungo¹; ¹Los Alamos National Laboratory
    Interfaces have been reported to significantly influence the deformation behavior of metallic nanolaminates, typically seen during nano-pillar experiments that observe hardness as a function of layer thickness. However, there is a lack of specific investigations on dislocation–interface interactions, their influence on the macroscopic behavior of these laminate structures, as well as the effect of interface character. Existing work performed atomistic simulations to capture such interface effects, while limited effort exists in modeling these systems using dislocation dynamics (DD). DD simulations provide a suitable framework to capture plasticity at nano-scales, and thus bridge the information between the (lower) atomistic and (higher) meso-scale models. In this work, we develop and implement an advanced interface model in an existing DD framework to simulate different interface behavior, as well as, accurately capture dislocation-interface interactions. Specifically, we identify the effect of different interface character on the bulk deformation behavior of these metallic nanolaminates.

9:20 AM
Strain-rate Dependent Deformation Mechanisms in Multilayer Cu/Mo Thin Films: Bibhu Prasad Sahu¹; Amit Misra¹; George M. Pharr²; ¹University of Michigan; ²Texas A&M University
    Strain-rate sensitivity and rate-dependent hardness, over a range of 10-2 to 102 s-1, of the sputter-deposited 5 nm Cu/ 5 nm Mo, and 100 nm Cu/ 100 nm Mo multilayer films with a total film thickness of 5 μm were measured using nanoindentation. Multilayer films exhibited enhanced hardness but slightly reduced strain-rate sensitivity with decreasing layer thickness from 100 nm to 5 nm. Only the 5 nm Cu/ 5 nm Mo multilayer film exhibited shear band underneath nanoindents and the size of the shear band increased with increasing strain rate. In contrast, the 100 nm Cu/ 100 nm Mo multilayer film exhibited material pile-up around indents and significant nanotwinning within Cu grains. The effect of strain rate and layer thickness on the hardness and strain rate sensitivity of the multilayer thin films is interpreted using a modified confined layer slip (CLS) model. The reduced rate sensitivity at 5 nm as compared to 100 nm is correlated with abundant growth nanotwins in the Cu grains in 100 nm and formation of shear bands in 5 nm multilayers.

9:40 AM
Orientation Dependence of Strength and Ductility in Nanolaminates Containing Interfaces with Three Dimensional Character: Justin Cheng¹; Shuozhi Xu²; Zezhou Li¹; Jonathan Poplawsky³; J. Kevin Baldwin⁴; Irene Beyerlein²; Nathan Mara¹; ¹University of Minnesota Twin Cities; ²University of California Santa Barbara; ³Oak Ridge National Laboratory; ⁴Los Alamos National Laboratory
    In nanolaminate composites, interface structure contributes strongly to mechanical behavior. This is due to a high density of interfaces, which can be designed to enhance mechanical properties. Recently, we have done so in Cu/Nb multilayers by introducing three dimensional (3D) interfaces between the pure constituent phases. 3D interfaces possess substantial thickness and are chemically, crystallographically, and topologically divergent from the phases that they separate. We present simultaneous enhancements in strength and plasticity arising from 3D interfaces in Cu/Nb with pure layer thickness of 10 nm. To elucidate the underlying mechanisms, we conduct cross-sectional TEM of micropillars compressed under different orientations. The link between interfacial structure and the high strength and plasticity observed will be discussed in terms of the atomic and mesoscale-level effects of collective dislocation motion in the presence of 3D interfaces.

10:00 AM Break

10:20 AM
Mechanistic-design of Multilayered Nanocomposites: Hierarchical Metal-MAX Materials for Tunable Strength and Toughness: Skye Supakul¹; Garritt Tucker²; Siddhartha (Sid) Pathak¹; ¹Iowa State University; ²Colorado School of Mines
    In this work we aim to tune the strength and toughness of a unique multilayered system, composed of alternating metallic and MAX phase layers (Nb – Ti₂AlC and Ti - Ti₃AlC₂) with a lamellar thickness reduced to the nanoscale, where the interfaces between the layers are in direct competition with the internal interfaces within the MAX layers. We demonstrate their (i) synthesis and (ii) mechanical response under extremes of temperature (cryo to 1000°C) and strain rate (10^-3 to 10³/s) and compare these responses to those of bulk MAX phases (Ta₂AlC). These micro-mechanical tests under extreme conditions were performed in both indentation and micro-pillar compression for varying layer thicknesses and local regions (orientations) to investigate their anisotropic mechanical behavior. Our results on bulk Ta₂AlC demonstrate differences in the measured activation volumes as a function of the grain orientation, suggesting changes in the deformation mechanisms of MAX phases with changing strain rates.

10:40 AM
Mechanical Behavior of Optimized Transparent Nanomultilayers: Danielle White¹; Edoardo Rossi²; Marco Sebastiani²; Andrea Hodge¹; ¹University of Southern California; ²Roma Tre University
    Nanomultilayers (NMs) are composite coatings with alternating material layers of thicknesses at the nanoscale. The highly tailorable NMs present a wide range of parameters which can be optimized for optical, electrical, magnetic or mechanical applications, for example. In this study, transparent optical nanomultilayers, AlN/SiO₂, TiO₂/SiO₂, and AlN/Al₂O₃, were optimized to yield a 94% average transmittance in the UV/Vis/NIR wavelength range. More interested in their multifunctional coating applications, nanoindentation, micropillar compression, and microtensile tests were performed on the optically optimized systems in order to correlate transmittance and microstructure to the mechanical behavior. Overall, different microstructures were observed depending on the NM configuration, leading to distinct failure behaviors.