100 Years and Still Cracking: A Griffith Fracture Symposium: Fracture of Thin Films
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Megan Cordill, Erich Schmid Institute of Materials Science; William Gerberich, University of Minnesota; David Bahr, Purdue University; Christopher Schuh, Northwestern University; Daniel Kiener, Montanuniverstität Leoben; Neville Moody; Nathan Mara, University of Minnesota; Erica Lilleodden, Fraunhofer Insitute for Microstructure of Materials and Systems (IMWS)
Tuesday 8:30 AM
March 16, 2021
Room: RM 47
Location: TMS2021 Virtual
Session Chair: Megan Cordill, Erich Schmid Institute
8:30 AM Invited
Leveraging Griffith’s Energy Balance in Extreme Environments: Timothy Weihs1; 1Johns Hopkins University
When materials impact each other at high velocities, multiple failure modes can occur such as spall and fragmentation. In this talk I describe collaborative efforts that leverage new experimental and computational methods to explore high-rate spall failure in Mg alloys and fragmentation in reactive solids following high-rate impacts. In the case of the magnesium alloys we identify the effects of grain size, texture and particle size on spall strength. In the case of reactive solids, we fabricate powder compacts with varying degrees of fracture toughness and then correlate these toughness values with the particle size distributions that result from fragmentation following impact. In both cases we explore how energy balances such as Griffith’s criterion can be used to describe void nucleation and fracture processes that contribute to spall and fragmentation during extreme, high-rate events.
9:10 AM
Fracture-based Reuse of Single Crystal Wafers for High-Efficiency Photovoltaics: Jie Chen1; Corinne Packard1; 1Colorado School of Mines
The spalling of a substrate is usually considered a detrimental phenomenon, where brittle fracture is induced by a tensile-stressed coating causing the critical strain energy release rate of the substrate to be exceeded. Intentional spalling in a process called ‘controlled spalling’ carefully engineers the initiation and propagation of brittle fracture to exfoliate layers of single crystal material to create flexible electronic devices or enable reuse of the substrate. Proof-of-principle device demonstrations have been achieved at wafer scale and in multiple configurations, showing no loss of performance compared to conventionally processed devices while preserving the wafer for reuse, reclaim, or recycling for cost and material savings. This review summarizes advances in controlled spalling as it relates specifically to III-V solar cells, covering advances in spalling-related methods development, process modeling and control, fracture surface morphology, and device processing and performance.
9:30 AM
Modeling Insights into Micro Single-Edge Bend Fracture Toughness Testing of Multilayered Metal-ceramic Cu/TiN and Al/TiN Nanocomposite Thin Films: Daniel Savage1; Shubhrodev Bhowmik2; Cayla Harvey3; Amit Misra4; Nathan Mara5; Jeffrey Wheeler6; Johann Michler7; Siddhartha Pathak8; Marko Knezevic2; 1University of New Hampshire/Los Alamos National Lab; 2University of New Hampshire; 3University of Nevada; 4University of Michigan; 5University of Minnesota; 6ETH Zürich; 7Empa, Swiss Federal Laboratories for Materials Science and Technology; 8University of Nevada/Iowa State University
Reliable extraction of fracture toughness in thin films of multilayered metal-ceramic Cu-TiN and Al-TiN nanocomposite systems is an outstanding problem and the micro single-edge bend (MSEB) test is a promising solution. In this work we systematically identify the effects of geometry, indenter stress field, and layer shielding effects on the determination of mode one fracture toughness using in-situ nanoindentation of MSEB specimens. Linear elastic finite element analysis is used to obtain local fields at experimental crack tip locations. The J and interface integral are used to isolate the effect of indenter stress field and give insight into the effectiveness of the material systems at preventing crack propagation. We find the leg geometry is significant in MSEB and show that changes in bending moment are driving increasing fracture toughness with decreasing crack ligament length. The design of geometry against bending moment variation is fundamental for MSEB standardization at small length scales.
9:50 AM Invited
Fracture and Adhesion in Small Scale Devices– Microswitches, Microcantilevers and Micron-thick Films: Maarten De Boer1; 1Carnegie Mellon University
Understanding how to control adhesion, friction and fracture is critical to the success of micro- and nanotechnologies. In devices such as microswitches, nanoswitches and MEMS actuators, adhesion is undesirable. Low values, one microJoule per square meter can be achieved, as limited by van der Waals forces. Understanding the role of humidity, temperature and adventitious hydrocarbons is key. We construct advanced chambers in which each factor is controlled and measure the deflections of microfabricated test devices with nanometer-scale resolution to determine adhesion values. In other instances, high adhesion is critical. We observe that a few seconds of electrodeposition can be responsible for delamination of a 1.5 micrometer thick underlying film. I will discuss the underlying hydrogen injection mechanism and how to achieve high adhesion when current efficiency is low.
10:30 AM
Improving Metal-polymer Adhesion through Alloy Development: Megan Cordill1; Patrice Krieml1; 1Erich Schmid Institute
Thin film transistor display technologies limit the lifetime of flexible displays due to the brittle fracture behavior of the currently used Mo/Al/Mo electrodes. In order to improve the electro-mechanical behavior of these electrode stacks the Mo adhesion layer was alloyed with suitable metals to increase its ductility, while maintaining good electrical conductivity and interface strength. Magnetron sputtered Mo thin films, alloyed with Al, Nb or Ta, on flexible Polyimide substrates were tested with monotonic in situ uniaxial tensile tests to evaluate their respective fracture resistance, electrical behavior, and adhesion energies to the polymer substrate. Mo-Ta has the best combination of low electrical resistivity with high crack onset strains and improved interface strength, thus shows the best prospects to substitute the Mo adhesion layers in flexible displays.
10:50 AM
Domain Nucleation in Ferroelastic Microcrystals: Competition between Twinning, Slip and Fracture: Jessica Krogstad1; Charles Smith1; 1University of Illinois at Urbana-Champaign
The mechanical behavior of single crystal, ferroelastic, tetragonal, ceria-titania-stabilized zirconia is evaluated through uniaxial micro-scale compression experiments. The deformed single crystal micropillars exhibit characteristics of several deformation modes, including twinning (ferroelastic domain nucleation), dislocation plasticity, and microcracking. Following earlier work that revealed how the onset of twinning obeys a critical resolved shear-stress law, much akin to Schmid’s law, we test this model and show that it does not hold for the data presented herein. We ascribe this discrepancy to the fact that multiple deformation mechanisms can be active in different microcrystals and even in the same microcrystals at room temperature, which is revealed by transmission electron microscopy. Whilst little is known about the potential interactions between these mechanisms at such low homologuous temperatures, their coexistence implies that crystal orientation alone is not sufficient to predict ferroelastic domain nucleation behavior in small-scale single crystals and ultimately toughening behavior afforded through ferroelasticity.