100 Years and Still Cracking: A Griffith Fracture Symposium: Fracture and Dislocations
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)

Monday 2:00 PM
March 15, 2021
Room: RM 47
Location: TMS2021 Virtual

Session Chair: Daniel Kiener, Montuniversität Leoben


2:00 PM  Invited
The Role of Fracture in the Reduction of Iron Ore with Hydrogen: Dierk Raabe1; 1Max-Planck Institute
    More than 1.8 billion tons of steel are produced per year, making it the most important alloy in terms of volume and impact. While steel is a sustainability enabler, through lightweight cars, wind farms and magnets, its primary production is not. Iron is reduced from ore using carbon. This produces >2t CO2 per t of steel, i.e. 30% of the CO2 emissions in manufacturing. These emissions can be reduced when replacing carbon by hydrogen as reductant. The kinetics of the reaction strongly depends on the ore’s chemistry and microstructure, specifically on damage and fracture associated with phase transformation and mass transport during reduction. Understanding these effects is key to make the hydrogen-based reduction of iron ores commercially viable, enabling massive CO2 reductions. This lecture reports about the recent progress in this research field, presenting results of a multi-scale structure and composition analysis of iron reduced from hematite with pure H2.

2:40 PM  Invited
Dislocation Pathways in Refractory Multi-principal Element Alloys: Fulin Wang1; Glenn Balbus1; Shuozhi Xu1; Yanqing Su2; Jungho Shin1; Paul Rottmann3; Keith Knipling4; Jean-Charles Stinville1; Leah Mills1; Oleg Senkov5; Irene Beyerlein1; Tresa Pollock1; Daniel Gianola1; 1University of California, Santa Barbara; 2Utah State University; 3University of Kentucky; 4U. S. Naval Research Laboratory; 5Air Force Research Laboratory
    Refractory multi-principal element alloys (MPEAs) are promising candidates for structural applications demanding mechanical robustness at temperatures exceeding the capacity of state-of-the-art superalloys. While excellent high temperature strength has been demonstrated in many refractory MPEAs, a fundamental understanding of the nature of dislocation pathways in the BCC versions of these chemically complex alloys and their ability to enable macroscopic ductility is still in its infancy. We present a study of a ternary MPEA, MoNbTi, through a combination of in situ dislocation observations, microstructural investigations, and atomistic calculations. Our results highlight multi-planar, multi-character dislocation slip in MoNbTi at low homologous temperature, encouraged by the substantial dispersion in the glide resistance for dislocation due to the atomic-scale chemical fluctuations. The ability of dislocations to choose the easy gliding direction and plane enables an excellent combination of strength and homogeneous plasticity in this alloy, traits that are not simultaneously observed in conventional metallic alloys.

3:20 PM  Invited
In Situ Observations and Measurements of Local Plastic Deformation and Fracture with 4D-STEM : Yang Yang1; Tom Pekin2; Ruopeng Zhang3; Shiteng Zhao3; Qin Yu1; Sheng Yin1; Colin Ophus1; Mark Asta3; Robert Ritchie3; Andrew Minor3; 1Lawrence Berkeley National Laboratory; 2Humbolt University, Berlin; 3University of California, Berkeley and Lawrence Berkeley National Laboratory
    In situ TEM experiments are typically recorded either in real space or diffraction space. However, it would be ideal to have information from both for when transient events occur that cannot be repeated exactly (ie- defect generation or irreversible phase transformations). 4D-STEM can come close to providing simultaneous real-space imaging and diffraction analysis during in situ testing, making it possible to perform strain mapping via diffraction pattern analysis during in-situ deformation in a TEM. This talk will highlight recent in situ 4DSTEM nanomechanical deformation experiments that explore transient events where both information from diffraction space and real space are used. The diffraction patterns are used to identify different phases, defects, orientations and relative strain, while the images formed by using virtual apertures provide microstructural context for the analysis. Example experiments include defect generation and fracture in multi-principal element alloys and bulk metallic glasses.

4:00 PM  
Dislocations Processes in Fracture and Toughening Mechanisms of UFG bcc Metals at Room Temperature: Inas Issa1; Anton Hohenwarter2; Jakub Zálešák1; Daniel Kiener1; 1Montanuniversität Leoben, Austria; 2Montanuniversität Leoben, Austria.
     We present in situ TEM fracture experiments on ultrafine-grained chromium (UFG, Cr) that reveal explicitly the occurrence of dislocation emission processes before intercrystalline fracture in UFG bcc metals at RT. These processes and related crack tip blunting serve as toughening mechanisms. Moreover, different in situ tests, with notches inside the grains or along grain boundaries (GBs) explicitly shows the importance of strengthening GBs as promising strategy in promoting further ductility and toughening in UFG bcc metals. Impurities such as Carbon or Boron acts as adhesion improving impurities that can modify the atomistic GBs configuration in front of the notch. We present a comparative mechanical study showing an improved ductility in UFG Cr- Carbon alloyed compared to pure UFG Cr. Electron Energy Loss Spectroscopy (EELS), TEM technique, is used to identify the Carbon segregation at GBs. This allows the understanding of how local segregation affects GBs cohesion and fracture toughness.

4:20 PM  
Imaging the Chemo-mechanical Coupled Fracture in Metal Passivation Layer by In-situ TEM: Yang Yang1; Akihiro Kushima2; Huolin Xin3; Peter Hosemann4; Ju Li5; 1Lawrence Berkeley National Laboratory; 2University of Central Florida; 3University of California, Irvine; 4University of California, Berkeley; 5Massachusetts Institute of Technology
    The mechanical performance of oxide scales is crucial for the stress corrosion resistance of metals. If cracks in oxide are generated during deformation or oxidation, embittering elements can diffuse into metal more easily, leading to greatly enhanced internal corrosion and materials degradation. Despite of the importance of oxide layers, the difficulty of imaging the environmental deformation of surface oxides at nanoscale has limited the understanding of their properties. Using an environmental TEM, here we report on in-situ experiments to overcome this challenge. We discovered that native alumina is liquid-like during deformation at room temperature, and it can remain its integrity without any cracks or spallation at moderate strain rate. On the contrary, zirconium quickly develops internal cracks during oxidation at 550 Celsius even without external forces. In this talk, we will discuss the chemo-mechanical coupled fracture in metal passivation layer and its impact on the stress-corrosion-cracking resistance.