Innovative Process Design and Processing for Advanced Structural Materials: Advanced Structural Materials
Program Organizers: Ju-Young Kim, UNIST; Jae-il Jang, Hanyang University; Sung-Tae Hong, University of Ulsan; Rongshan Qin, The Open University
Tuesday 8:00 AM
October 11, 2022
Room: 327
Location: David L. Lawrence Convention Center
Session Chair: Ju-Young Kim, UNIST; Jae-il Jang, Hanyang University
8:00 AM Break
8:20 AM
Uniaxial Tensile Behavior After Baking Treatment in a Low Carbon Steel Accompanying Inhomogeneous Plastic Yielding: Woojin Cho1; Byeong-Seok Jeong1; Eunjoo Shin2; Siwook Park1; Hyuntaek Na3; Heung Nam Han1; 1Seoul National University; 2Korea Atomic Energy Research Institute; 3POSCO Technical Research Laboratories
In this study, two kinds of steels with the same composition accompanying yield point phenomenon during the uniaxial tensile test were prepared; one is composed of the acicular ferrite with pre-existing mobile dislocations and the other is the annealed polygonal ferrite with few mobile dislocations. Pre-strains were applied to these steels at 25, 50, 75, and 100% of the strain where the Lüders band (LB) completely propagated to the gauge section. Until the LB fully propagate to the gauge section, no bake hardening (BH) response was observed for in either steel. However, when the LB completely propagated to the gauge section (100%), we can confirm BH response appeared considerably in both specimens. This BH behavior was analyzed through digital image correlation technique and macro-indentation tests. Additional changes in uniaxial tensile behavior e.g., total elongation, yield point phenomenon, and tensile strength was discussed utilizing nano-indentation and small angle neutron scattering.
8:40 AM
On the Micromechanical Response of a Mild Steel during Abrupt Strain Path Changes (SPCs): Anastasia Vrettou1; Hiroto Kitaguchi1; Biao Cai1; Thomas Connolley2; David Collins1; 1University of Birmingham; 2Diamond Light Source Ltd
The effect of Strain Path Changes (SPCs) on the mechanical properties and crystal-level deformation for a single phase, ferritic steel is studied. SPCs were applied via a two-step deformation process, including pre-straining via cold rolling, then uniaxial tension. The role of texture and micromechanics were examined in-situ, by Synchrotron X-Ray Diffraction, and ex-situ, by Electron Backscatter Diffraction. Strain paths with orthogonal major strains result in lower ductility, becoming more prevalent at high pre-strains. The macroscopic response and texture were dependent on the pre-strain direction but were insensitive to the uniaxial tension direction. Increasing pre-strain magnitudes resulted in stagnation of lattice strain hardening rates in all macroscopic directions and a significant increase in the geometrically necessary dislocation density. This was increased for specimens rolled perpendicular to the initial rolling direction. The initial and developed texture from the pre-strain influences the density of dislocations accumulated in all grains, and ultimately determines ductility.
9:00 AM
A Study on Migrating Boundary Induced Plasticity Using Molecular Dynamics Simulation for Pure Iron: Simoon Sung1; Jaehoon Jang2; Yanghoo Kim3; Heung Nam Han1; 1Seoul National University; 2Korea Institute of Materials Science; 3Korea Institute of Industrial Technology
It has been observed that a permanent deformation occurs during solid-solid phase transformation of ferrous or other alloys, even when subjected to stress much lower than the yield stress. This phenomenon, which is known as transformation plasticity or transformation induced plasticity, is known to cause many engineering problems. Interestingly, a similar phenomenon was observed during recrystallization and grain growth. To explain the phenomenon, the concept of migrating boundary induced plasticity (MIP) had been suggested. In this presentation, we used a molecular dynamics (MD) simulation to confirm the presence of a significant amount of permanent deformation that occurs during grain growth under external stress. And it was found that this permanent deformation is a thermal activation process, which is consistent with the MIP. Based on these results, a newly modified phenomenological MIP model was proposed, and this modified MIP model was able to explain the permanent deformation obtained by MD results.
9:20 AM
Mechanisms Driving Defect Formation in High Power Laser Welding of Nickel Alloys: Mingze Gao1; Barnali Mondal1; Todd Palmer1; Tarasankar Debroy1; 1Penn State University
High power laser welding produces deep penetrations, which also display unique processing conditions far different from arc welding or low power laser welding and enhance susceptibility to defects. To better understand the mechanisms driving these defects, high power laser welding was conducted on three widely used nickel alloys. Among these alloys, Inconel 690 is most susceptible to keyhole collapse porosity. On the other hand, Inconel 740H displayed higher susceptibility to hot cracking than Inconel 718 while no such defect was found in Inconel 690. Thermodynamic calculations were conducted to investigate the role of alloying elements on solidification path, which also allows for the evaluation of hot cracking susceptibility. A validated heat transfer and fluid flow model for keyhole mode laser welding was employed to capture the spatially variable thermal histories, fluid flow, and solidification conditions. Local variations in these processing conditions were correlated with the occurrence of location dependent defects.
9:40 AM Invited
Microstructure-based Fatigue Life Modeling Methodology for Ferritic-pearlitic Hypo-eutectoid Steels: Yoon Suk Choi1; Minwoo Park1; Hyunki Kim2; Minwoo Kang2; Seunghyun Hong2; Dae-Geun Nam3; 1Pusan National University; 2Hyundai Motor Group; 3Korea Institute of Industrial Technology
A microstructure-based fatigue life prediction methodology was proposed and verified for 44MnSiVS6 hypo-eutectoid steel. As a first step, a statistically equivalent synthetic microstructure generation algorithm was developed by applying the cellular automata under the multi-level microstructure generation approach, and verified by comparing to the real microstructure. Crystal plasticity-based elasto-viscoplastic constitutive models were developed for the primary ferrite and pearlite, and their constitutive parameters were calibrated. Synthetic microstructure-based crystal plasticity finite element simulations (CP-FEM) were performed for stress-controlled axial fatigue tests. The Fatemi-Socie (FS) parameter was chosen to calculate a fatigue indicator parameter increment per cycle (dFIP), and its cumulative distribution probability (CDP) curve was obtained from CP-FEM simulations. Three different criteria extracting a representative dFIP from the CDP curve were proposed after thoroughly examining the nature of the CDP curves. Extracted representative dFIP values coupled with the Power law-based model gave reasonable fatigue life prediction.
10:00 AM Break
10:20 AM Invited
Modern Supercomputing for Accelerating the Design of High-temperature Aluminum Alloys
: Dongwon Shin1; 1Oak Ridge National Laboratory
The volume of available data for aluminum alloys is counterintuitively much smaller than the community expects due to the relatively short research history. Nevertheless, the demand for designing and deploying advanced aluminum alloys for industrial applications has increased dramatically. The challenge is that the anticipated timeframe of alloy development is getting shorter than it used to be because of market competitiveness. This presentation will introduce the use of modern high-performance computing to rapidly populate high-fidelity data toward aluminum alloys design. Examples are constructing first-principles databases of solute segregation energies at the interface between key precipitate and aluminum matrix and solute-vacancy clustering in aluminum. This research was supported by the U.S. Department of Energy, Office of Energy Efficiency, and Renewable Energy Vehicle Technologies Program.
10:40 AM
Atomic-scale Unique Interface Observation of η/Al in Al-Zn-Mg Alloy: Hwangsun Kim1; Howook Choi1; Juhyun Oh1; Ho Kwon1; Eun Soo Park1; Sungwoo Lee1; Gun-Do Lee1; Miyoung Kim1; Heung Nam Han1; 1Seoul National University
Al-Zn-Mg alloys have been widely used in automobile and aerospace industry due to its lightweight property and high strength. The main strengthening mechanism of Al-Zn-Mg alloy is known as precipitation hardening. The precipitation sequence has been reported as follows: Super-saturated solid solution → GP zones → η’ phase → η phase. Among the 15 differently oriented η precipitates, η1, η2, and η4 have the highest proportion and the rest except for these are known to exist less than 1%. In this study, η4 precipitates, which is mainly precipitated when heterogeneous nucleation occurs, were observed in atomic scale and it was confirmed that it has a pseudo-periodic step-like interfacial structure with Mg and Zn segregation. We compared the interface energy of simulated flat interface and experimentally observed unique interface using ab-initio calculation. Consequently, the unique interface was energetically favored.
11:00 AM
Virtual Thermo-mechanical Process Design of Metallic Materials by Integrating Crystal Plasticity and Phase Field Model: Kyung Mun Min1; Hyuk Jae Lee1; Heung Nam Han1; Myoung-Gyu Lee1; 1Seoul National University
In this study, a computational approach is proposed to simulate a thermo-mechanical process consisting of cold rolling followed by annealing. From microstructural information of as-received hot-rolled sheet, crystal plasticity finite element model incorporating dislocation density based constitutive laws is accounted for to calculate the deformation and stress development during the cold rolling process, while a phase field model can reproduce microstructure evolution of the cold-rolled sheet during an annealing process. Particularly, the current modeling framework accounts for the shear band formation to evaluate the effect of the shear band on texture evolution during both rolling and annealing. Predicted microstructure and its effect on mechanical behavior are discussed by the proposed virtual thermo-mechanical process under various process factors. Finally, the calculated mechanical responses and microstructures are validated by comparing them with experimental data to estimate the accuracy of the model.