Deformation-induced Manipulation of Defect Structures and Hierarchical Microstructures: Session II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Bharat Gwalani, North Carolina State Universtiy; Kester Clarke, Los Alamos National Laboratory; Eric Lass, University of Tennessee-Knoxville; Vahid Tari, ATI - Allegheny Technologies Incorporated
Wednesday 2:00 PM
March 22, 2023
Room: Sapphire P
Location: Hilton
Session Chair: Kester Clarke, Colorado School of Mines; Michael Lastovich, North Carolina State University; Eric Lass, University of Tennessee-Knoxville
2:00 PM Invited
Dynamically Reversible Shear Transformations in a CrMnFeCoNi High-entropy Alloy: Jian Wang1; Kaisheng Ming2; Shijian Zheng2; 1University of Nebraska-Lincoln; 2Hebei University of Technology
Shear transformation, such as twinning and martensitic phase transformation, is generally unidirectional under monotonic thermal or mechanical loading. By tailoring stacking fault energy (SFE) and taking advantage of low temperature deformation, we achieve the dynamically reversible shear transformations in CrMnFeCoNi high-entropy alloys (HEAs) under uniaxial tension at cryogenic temperature. Plastic deformation is accommodated by dislocation slips and shear transformation bands, such as {111} stacking faults (SFs), {111} nano-twins, fcc → hcp shear transformation bands, high-density {0001} SFs and {1"0" 1 ̅1} nano-twins. More intriguingly, hcp → fcc shear transformations are stimulated by deformation-induced local dissipative heating. The reversible fcc ↔ hcp shear transformations and both {1"0-1" 1} and {111} nano-twinning lead to dynamic nano-laminated dual-phase (NL-DP) structures, which advances the monotonic “dynamic Hall-Petch” effect in enhancing strength, strain-hardening ability, and ductility by dynamically tailoring the type and width of shear transformation bands.
2:20 PM Invited
Grain Refinement and Microstructural Evolution in AM High Entropy Alloys through SPD and Thermomechanical Processing: Benjamin Adam1; Megumi Kawasaki1; Tianyi Chen1; 1Oregon State University
Additive manufacturing (AM) techniques are of current interest to advance the synthesis and application of novel high-performance structural alloys such as High Entropy Alloys (HEA). Advantages of AM over conventional manufacturing in processing complexity are balanced with the need for post-process thermo-mechanical treatment to achieve optimal in-service mechanical properties. Here we explore effects of severe plastic deformation (SPD) through Equal Angular Channel Processing (EACP) and High Pressure Torsion (HPT) and thermomechanical processing through hot compression on microstructure-property relationships in AM-built samples. Each processing step is analyzed for evolution of grain size, morphology, and texture using electron backscatter diffraction and scanning electron microscopy techniques. In-situ mechanical testing through nanoindentation provides complementary data at micro scale on hardness, elastic modulus and plasticity of the material. Results will aid in understanding the link between initial as-built microstructure and final mechanical properties, and populate gaps in datasets for materials synthesized using advanced manufacturing techniques.
2:40 PM Invited
Exploring Joining Mechanism for Immiscible System: Friction Stir Welding of Pure Mg and Pure Fe: Hrishikesh Das1; Bharat Gwalani1; Xiaolong Ma1; Piyush Upadhyay1; 1Pacific Northwest National Laboratory
While welding various Mg alloys and steels has a direct impact on structural light-weighting in automobile industries, joining pure Mg and pure Fe is scientifically crucial to understanding the joining mechanism. Three pairs of dissimilar FSW joints: (AZ31-DP590), (Pure Mg-DP590) and (Pure Mg-Pure Fe) were studied to shed light on joining mechanisms responsible for bonding of “immiscible” pairs of Mg and Fe. Transmission electron microscopy (TEM) and atom probe tomography (APT) were conducted at the interface. In the case of AZ31-DP590, the interface was mediated by a nano scale thin layer of segregated Al. A complex Al/Mg oxide layer is also found at the interface. In case of pure Mg-DP590, the interface consists of nano scale oxygen rich layer which may act as a bridging layer between the two immiscible system via lattice matching. Whereas Pure Mg and pure Fe were bonded by a critical interfacial MgO/FeO/Fe nano-crystalline oxide layer.
3:00 PM
Effect of Pre-straining on High Strain Rate Compression Behavior of a Complex Concentrated Alloy Exhibiting Transformation Induced Plasticity: Ravi Sankar Haridas1; Priyanka Agrawal1; Jeffrey T Lloyd2; Rajiv Mishra1; 1University of North Texas; 2CCDC Army Research Laboratory
Metastability-based alloy design strategy enabled engineering of complex concentrated alloys (CCAs) which exhibit transformation induced plasticity (TRIP) under deformation. Sequential evolution of deformation mechanisms such as slip, twinning, and transformation in both parent and transformed phases provided excellent strength-work hardening-ductility synergy to the alloy. Inclusion of microstructural interfaces in the form of twin boundaries and martensitic boundaries by pre-straining showed improved mechanical properties in TRIP CCAs via massive interfacing. Present study investigated the effect of static pre-compression on the dynamic response of a TRIP Fe38.5Mn20Co20Cr15Si5Cu1.5 CCA in homogenized and friction stir processed (FSP) conditions. Primary martensitic bands formed during static compression acted as precursors for secondary martensitic band formation and deformation twinning, thereby imparting excellent resistance to the alloy at high strain rate via massive interfacial strengthening. Also, the grain refinement by FSP restricted the interface formation during pre-compression, and resulted in alternate dynamic response and deformation evolution.
3:20 PM
Deformation of Fe-Rich, Co-Free Multi-Principal Element Alloys at Multiple Strain Rates and Temperature Conditions: James Frishkoff1; Kester Clarke1; Amy Clarke1; 1Colorado School of Mines
Multi-principal element alloys (MPEAs) have been shown to exhibit novel and desirable mechanical properties, including high strength – ductility combinations and compositionally and microstructurally tunable deformation mechanisms. However, most MPEA mechanical property measurements are made at room temperature under quasi-static strain rate conditions. Given that deformation mechanisms in metals and alloys are temperature and strain rate dependent, understanding the mechanical response of MPEAs under varied thermal and strain rate conditions is important to their phase stability and microstructure evolution, processing, and potential service in demanding applications. A set of Fe-rich MPEAs were designed and subjected to variable strain rate and temperature mechanical testing in a Gleeble® thermomechanical processing simulator. Constitutive relations were derived from these tests. Microstructural evolution with deformation was assessed via x-ray diffraction and electron backscatter diffraction, and temperature and strain rate dependence of deformation mechanisms is discussed.
3:40 PM Break
4:00 PM
Deformation Mechanisms in Cu-Nb Nanolayered Composite under Pico-indentation and Tribological Testing: Mayur Pole1; Zexi Lu1; Tanvi Ajantiwalay1; Matthew Olszta1; Shalini Tripathi1; Anqi Yu1; Hardeep Mehta1; Tianhao Wang1; Xiaolong Ma1; Arun Devaraj1; Bharat Gwalani1; 1Pacific Northwest National Laboratory
Two-phase nanolayered composites with a high density of semicoherent interfaces exhibit excellent mechanical properties and thermal stability. In this study, magnetron sputtered Cu-Nb nanolayered composite having an amorphous interface between Cu and Nb with highly aligned growth twins in Cu is subjected to severe surface deformation by pico-indentation and high strain cyclic shear loading. The subsurface deformed microstructure reveals multiple deformation mechanisms with grain refinement and crack formations in the highly stressed region of the Nb layer and localized crystallization of the amorphous interface. In addition, detwinning of unstable growth twins in the Cu layer under the cyclic shear strain leaves large dislocations sites and loops which are observed both by high-resolution transmission electron microscopy and experiment guided molecular dynamic simulations.
4:20 PM
Deformation Induced Hierarchical Twinning in Titanium Alloys: Dian Li1; Yufeng Zheng1; 1University of Nevada, Reno
Microstructure evolutions in metastable beta titanium alloys can be tuned using a number of defect structures, such as grain boundary, dual-phase interface and pre-formed twin boundary. In our recent studies, we have found that the highly-indexed deformation twins in the cold-rolled metastable beta Ti-5Al-5Mo-5V-3Cr alloy (wt.%, Ti-5553) can assist the formation of hierarchical alpha microstructure during the subsequent heat treatment. In this work, we studied the nanoscale substructure in the hierarchical highly-indexed deformation twinning systems in the cold rolled Ti-5553 and Ti-24Nb-4Zr-8Sn (wt.%, Ti-2448) alloys using the diffraction contrast TEM and z-contrast aberration-corrected S/TEM. At the twin boundary, a nanoscale layer of metastable phase was observed and while in the interior of the twin, nanoscale metastable phases including omega phase and alpha” phase were characterized. The formation mechanisms of the hierarchical twinning in these titanium alloys will be discussed. This work is supported by the National Science Foundation, grant CMMI-2122272.
4:40 PM
A Novel Warm Rolling Induced Microstructure Modification for Evading Strength-Ductility Trade-off in Medium Manganese Steel: Avanish Chandan1; Gyanaranjan Mishra2; Kaushal Kishore2; Jay Chakraborty1; 1CSIR- National Metallurgical Laboratory; 2Tata Steel Ltd
In the present work, modification of microstructure via a novel warm rolling (WR) treatment is shown to overcome the strength-ductility trade-off in a medium manganese steel. Controlled generation of dislocations (~1015 m-2) in the constituent austenite and ferrite phases along with introduction of twins in the austenite phase, both induced by WR fetched a 32% improvement in YS as compared to the conventional intercritically annealed (IA) specimen. Additionally, austenite stability regulation via dislocations led to simultaneous improvement in UTS and ductility by 12% and 6%, respectively, as compared to the IA specimen. YS (~952±8 MPa), UTS (~1252±13 MPa) and ductility (~30±3 %) obtained in the warm-rolled specimens was significantly high considering the composition of the steel i.e. without any microalloying. The present study demonstrates an approach to tailor the defect microstructure for escaping the near-ubiquitous strength-ductility paradox in metastable FCC alloys such as stainless steel, HEAs, TWIP steels etc.