Heterostructured and Gradient Materials (HGM V): New Mechanistic Discoveries Enabling Superior Properties: Processing and Properties
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Shaping and Forming Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Yuntian Zhu, City University of Hong Kong; Kei Ameyama, Ritsumeikan University; Irene Beyerlein, University of California, Santa Barbara; Yuri Estrin, Monash University; Huajian Gao, Nanyang Technological University; Ke Lu, Institute of Metal Research; Suveen Mathaudhu, Colorado School of Mines; Xiaolei Wu, State Institute of Mechanics, Chinese Academy of Sciences
Tuesday 8:00 AM
March 21, 2023
Room: Aqua 314
Location: Hilton
Session Chair: Nobuhiro Tsuji, Kyoto University; Rajiv Mishra, University of Northern Texas
8:00 AM Invited
Heterogeneous Microstructure Driven Strength-ductility Synergy in Laser Powder Bed Additively Manufactured Alloys: Rajiv Mishra1; 1University of North Texas
There is significant interest in alloys with heterogeneous microstructures, particularly for strength-ductility synergy. The timing of research on heterogeneous and gradient alloys coincides very well with tremendous volume of research on laser powder bed additive manufacturing (LPBAM). While the component design opportunities with LPBAM have been discussed very widely, the potential of control of site-specific microstructure in components has not received that much attention. In this overview presentation, the opportunity to tailor the microstructure will be highlighted. Our work on novel Al alloys designed for printability-performance synergy during LPBAM provided a nice window for obtaining heterogeneous microstructure. The fundamentals behind this approach will be presented. These finding can be generalized to other alloys, and to properties beyond the strength-ductility paradigm. A few general guidelines will be discussed.
8:30 AM
Effect of Grain Refinement on Plastic Deformation and Fracture in a Si-added High-Mn Austenitic Steel: Sukyoung Hwang1; Yu Bai2; Si Gao1; Akinobu Shibata3; Nobuhiro Tsuji1; 1Kyoto University; 2Dalian University of Technology; 3National Institute for Materials Science (NIMS)
High-Mn austenitic steels are well known for their outstanding mechanical properties combining high strength and large ductility, which are believed to result from the formation of mechanical twins during plastic deformation. Meanwhile, the low yield strength of high-Mn austenitic steels has always been an issue for practical applications. Grain refinement is an effective way to improve the low yield strength of polycrystalline material according to the Hall-Petch relationship.In the present study, 22Mn-0.6C-3Si (mass %) steels with various mean grain sizes down to ultrafine grained (UFG) region were successfully fabricated by high pressure torsion (HPT) and subsequent annealing. The present material showed a unique tensile behavior that the strength and ductility simultaneously increased with the grain refinement. The effect of grain refinement on the mechanical properties are discussed in relation to the deformation microstructures, and detailed results are shown and discussed in the presentation.
8:50 AM
High Strength and Ductility in a Heterostructured Nanotwinned Ni Film: Rohit Berlia1; Jagannathan Rajagopalan1; 1Arizona State University
We report the synthesis and mechanical behavior of two nanotwinned (NT) Ni films, one with a uniform distribution of twin widths and the other with a heterogeneous distribution of twin widths. The NT Ni films, deposited on Si (111) substrates with an Ag buffer layer, are composed of two crystallographic variants with (111) out-of-plane orientation, which results in the formation of twin boundaries between them. While both films exhibited an ultimate tensile strength of over 1 GPa, the film with heterogeneous twin structure showed significant strain hardening as well, which led to uniform elongation of ~10%. These results suggest that by introducing heterogeneity in the twin width distribution it is possible to realize a synergistic combination of strength and ductility in NT metal films.
9:10 AM
Improving Local Fracture Properties of W-CuZn Nanocomposites by Microstructure Tailoring: Daniel Kiener1; Klemens Schmuck1; Markus Alfreider1; Michael Burtscher1; Michael Wurmshuber1; 1University of Leoben
Tungsten offers outstanding material properties for high performance applications in harsh environments, but commonly lacks damage and fracture tolerance due to a high ductile to brittle transition temperature. By creating a composite involving copper as ductile phase, the damage and fracture tolerance are increased at the expense of material strength. Hence, additional strengthening of the ductile phase is desirable, i.e. by alloying copper with zinc. Such W-CuZn nanocomposites were produced by severe plastic deformation, and microstructural investigations by means of SEM, TEM and TKD provided insights regarding the microstructural evolution. In-situ SEM fracture experiments on FIB milled micro-cantilevers were conducted to analyze crack growth and determine the material's fracture toughness. We show that the saturation grain size depends on the ductile phase strength and HPT deformation temperature. Furthermore, fracture analysis reveals that the fracture process is dominated by intercrystalline failure and that primarily inhomogeneities determine the achievable fracture toughness.
9:30 AM Break
9:50 AM
Modeling of Back Stresses in Additively Manufactured Stainless Steel: Kunqing Ding1; Yin Zhang1; David McDowell1; Ting Zhu1; 1Georgia Institute of Technology
Additively manufactured stainless steel exhibits high yield strength and strain hardening due to printing-induced sub-micron dislocation cell structures. The as-printed dislocation cells hinder dislocation glide during plastic deformation, producing strong back stresses. We develop models of microscale internal stresses in AM stainless steel by focusing on their back stress components. Three sources of back stresses are considered, including the printing and deformation-induced back stresses associated with as-printed dislocation cells as well as the deformation-induced back stresses associated with grain boundaries. A dislocation pile-up model is adopted to evaluate the deformation-induced back stresses associated with as-printed dislocation cells. The extracted back stress relation from the pile-up model is incorporated into a crystal plasticity model. The associated finite element simulation results agree with the experimentally measured back stress and tension-compression asymmetry. Our results provide an in-depth understanding of the origins and evolution of back stresses in AM metallic materials.
10:10 AM
Quasi-static and Dynamic Mechanical Behavior of Metal Composites with Co-continuous Phase Distributions: Lauren Poole1; Avery Samuel1; Ashley Hilmas2; Frank Zok1; 1University of California Santa Barbara; 2Air Force Research Laboratory
The dynamic mechanical behavior of multiphase metal composites comprising dissimilar immiscible phases can be controlled through selection of constituents, processing routes and phase topologies. Here, we experimentally and computationally investigate a co-continuous tungsten-copper composite that is of interest because both constituents exist in significant fractions and exhibit highly dissimilar properties (CTE, density, yield stress, elastic modulus, crystal structure). First, quasi-static and dynamic loading experiments study how the strengths and rate sensitivities of the constituent phases manifest in the bulk composite’s response. Second, CT reconstructions of the composites are used to characterize phase connectivity for development of representative finite element models. These models can be extended to study a broad range of compositions to gain general insights into composites with co-continuous phase distributions.