Browsing by Author "Lee, Soo Yeol"

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Characterization of Deformation and Wear Mechanisms During Indentation Scratching on Pure Zinc
(2020-01-01)
Gokhale, Aditya
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Jain, Jayant
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Prasad, Rajesh
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Huang, E-Wen
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Lee, Soo Yeol
Scratch testing using nanoindentation helps to characterize material's wear resistance and the accompanying material removal, and deformation mechanism. The effect of load and repeated scratching on pure zinc was investigated in this study. Surface examination post scratching revealed the formation of long chips at lower loads, which can be attributed to ductile-like behavior. Ploughing dominated at higher loads, while micro-cutting was active at lower loads. The material removal factor (f(ab)) is an indicator of the prevailing wear mechanism. A good correlation appeared between the observed wear mechanism and the calculated fab, wherein interplay of ploughing and micro-cutting was observed. The decrease in wear rate as the number of passes increased and the decreasing value of fab are indicative of the strain hardening behavior during repeated scratching. The presence of intergranular fracture slip and twinning on the deformed surface is indicative of the material's response to induced stress.
Comparing Cyclic Tension-Compression Effects on CoCrFeMnNi High-Entropy Alloy and Ni-Based Superalloy
(2019-08-01)
Lam, Tu-Ngoc
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Chou, You-Shiun
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Chang, Yao-Jen
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Sui, Tsung-Ruei
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Yeh, An-Chou
An equal-molar CoCrFeMnNi, face-centered-cubic (fcc) high-entropy alloy (HEA) and a nickel-based superalloy are studied using in situ neutron diffraction experiments. With continuous measurements, the evolution of diffraction peaks is collected for microscopic lattice strain analyses. Cyclic hardening and softening are found in both metallic systems. However, as obtained from the diffraction-peak-width evolution, the underneath deformation mechanisms are quite different. The CoCrFeMnNi HEA exhibits distinct lattice strain and microstructure responses under tension-compression cyclic loadings.
Crystal plasticity modeling and neutron diffraction measurements of a magnesium AZ31B plate: Effects of plastic anisotropy and surrounding grains
(2020-02-01)
Wang, Huamiao
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Lee, Soo Yeol
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Huang, E-Wen
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Jain, Jayant
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Li, Dayong
This study used in-situ neutron diffraction measurements and Elastic ViscoPlastic Self-Consistent polycrystal plasticity model, which incorporates a Twinning and DeTwinning scheme (denoted by EVPSC-TDT), to examine the macro-and micro-mechanical behaviors of a rolled AZ31B plate subjected to uniaxial tension. Three specimens were specifically designed for minimum, maximum and intermediate twinning: (1) loading along the rolling direction, (2) loading along the plate normal, and (3) loading along the direction 45 degrees with respect to the plate normal. Apart from the macroscopic stress strain response, the measured diffraction intensities and internal elastic strains were obtained to examine the activities of the deformation modes at the grain level. The diffraction intensity evolution signaled the volume fraction change of twinning, while the internal elastic strain evolution designated the stress partitioning among the grain orientations. The effect of the surrounding grains on the development of the internal elastic strain was investigated by identifying the corresponding deformation mechanisms. Notably, the corresponding modeling work revealed that the EVPSC-TDT model permitted the prediction of the strain hardening and anisotropic behavior along the directions with minimum, maximum and intermediate twinning at the macroscale, and the evolution of the diffraction intensities and internal strains at the microscale. The results provide a physical understanding of the effects of the load direction, texture and surrounding grains on the role of the deformation modes in hexagonal close-packed polycrystalline materials. (C) 2019 Elsevier Ltd. All rights reserved.
Dynamic Strain Evolution around a Crack Tip under Steady- and Overloaded-Fatigue Conditions
(2015-12-01)
Lee, Soo Yeol
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Huang, E-Wen
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Woo, Wanchuck
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Yoon, Cheol
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Chae, Hobyung
Hardening steels by the generation of transient phase using additive manufacturing
(2019-06-01)
Huang, E-Wen
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Lee, Soo Yeol
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Jain, Jayant
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Tong, Yang
;
An, Ke
In the present work, the tensile properties of 15-5 PH steel fabricated by selective laser melting (SLM) were examined with respect to the transient austenite phase. Compared with the 8%-transient-phase sample, the 18%-transient-phase one shows higher ultimate tensile strength and relatively low yield strength, as well as hardening behavior. We conducted in-situ neutron-diffraction study to examine the microstructure evolution for mechanistic understanding. After applying the external load, most non-equilibrium, retained austenite in the 8% transient-phase sample transforms before the yield strength, whereas in the 18%-transient-phase sample only 50% of the austenite transforms. Accompanying with the phase transformation, a decrease in the dislocation density and the dislocation strain energy-assisted phase transformation of the ferrite phase are found in the 8%-transient-phase sample even before yielding, which, however, is not the case in the 18%-transient-phase sample. The study demonstrates the SLM enables tuning the amount of transient-phase ratio and coherency between phases to realize a mechanical property control for additive manufactured steel.
Irreversible phase transformation in a CoCrFeMnNi high entropy alloy under hydrostatic compression
(2018-03-01)
Huang, E-Wen
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Lin, Chih-Ming
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Jain, Jayant
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Shieh, Sean R.
;
Wang, Ching-Pao
An equal-molar CoCrFeMnNi, face-centered-cubic high-entropy alloy system is investigated using in-situ angular-dispersive X-ray diffraction under hydrostatic compression up to 20 GPa via diamond anvil cell. The evolutions of multiple diffraction peaks are collected simultaneously to elucidate the phase stability field. The results indicated that an irreversible phase transformation had occurred in the high entropy alloy upon decompression to ambient pressure. A reference material (n-type silicon-doped gallium arsenide) was investigated following the same protocol to demonstrate the different deformation mechanisms. It is suggested that the atomic bonding characteristics on the phase stability may play an important role in the high entropy alloys.
Mechanical and Magnetic Properties of the High-Entropy Alloys for Combinatorial Approaches
(2020-03-01)
Huang, E-Wen
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Hung, Guo-Yu
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Lee, Soo Yeol
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Jain, Jayant
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Chang, Kuan-Pang
This review summarizes the state of high-entropy alloys and their combinatorial approaches, mainly considering their magnetic applications. Several earlier studies on high-entropy alloy properties, such as magnetic, wear, and corrosion behavior; different forms, such as thin films, nanowires, thermal spray coatings; specific treatments, such as plasma spraying and inclusion effects; and unique applications, such as welding, are summarized. High-entropy alloy systems that were reported for both their mechanical and magnetic properties are compared through the combination of their Young's modulus, yield strength, remanent induction, and coercive force. Several potential applications requiring both mechanical and magnetic properties are reported.
Nanowear Mechanisms of Mg Alloyed with Al and Y at Elevated Temperatures
(2020-03-03)
Gokhale, Aditya
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Meena, Trapesh
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Lee, Soo Yeol
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Huang, E-Wen
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Gosvami, Nitya N.
We examine the role of important alloying elements (Al, Y), on friction and wear mechanisms of Mg as a function of temperature. Friction and wear tests of Mg-5%Al and Mg-5%Y alloys performed at room temperature, 100 degrees C and 150 degrees C reveal that addition of Al and Y significantly reduces the coefficient of friction. However, despite higher hardness of Mg-5%Y alloy, its wear rate was found to be higher than Mg-5%Al alloy at elevated temperatures. We show that this behaviour, observed for Mg-5%Y alloy at elevated temperature, can be attributed to its higher surface energy than Mg-5%Al and pure Mg, leading to enhanced adhesive wear, which is detrimental to tribological applications.
Neutron diffraction residual stress analysis during fatigue crack growth retardation of stainless steel
(2017-11-01)
Seo, Sukho
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Huang, E-Wen
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Woo, Wanchuck
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Lee, Soo Yeol
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材料科學與工程學系
After tensile overloading during fatigue crack growth, retardation, of the crack growth rate was significant. Neutron diffraction was employed to examine the evolution of crack-tip residual stress fields during constant-amplitude cyclic loading and during fatigue crack growth following the overload. It was found that the tensile overload induces larger compressive residual stress and zone size near the crack tip in the crack-growth and crack-opening direction. For the maximum crack growth retardation, the largest compressive residual stresses were measured in the region between an overloading point and the current propagating crack tip, for all three of the orthogonal directions. Such large compressive residual stresses in the crack-wake region are thought to reduce the crack tip driving force, thereby retarding the crack propagation rate significantly. Residual stress mapping was performed to examine the effect of the fatigue stress state on the residual stresses in the three different regions from the centerline to the surface, along the through-thickness direction in the compact-tension specimen. Much larger compressive residual stresses were measured at the surface than at mid-thickness. It is thought that larger compressive residual stresses at the surface result from the plane stress condition, resulting in a slower fatigue crack growth rate at the surface of the specimen. (C) 2017 Elsevier Ltd. All rights reserved.
On plastic anisotropy and deformation history-driven anelasticity of an extruded magnesium alloy
(2020-02-01)
Wang, Huai
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Lee, Soo Yeol
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Wang, Huamiao
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Woo, Wanchuck
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Huang, E-Wen
The plastic anisotropy and unloading anelasticity of an extruded Mg-9 wt.%Al alloy (with two annealed textures) were investigated using in-situ neutron diffraction measurement and crystal plasticity modelling. The distinctive yielding and hardening behaviors during compressive and tensile loading-unloading cycles were interpreted by the alternative operations of different slip/twinning modes. We reveal that the micromechanical responses of differently-oriented grains strongly depend on their neighboring conditions and operative deformation mechanisms. Based on the modelling results, unloading anelasticity is hypothesized to be controlled by the plastic contribution of the hard deformation mode and its impeding effects on easier deformation modes. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Phase Stress Partition in Gray Cast Iron UsingIn SituNeutron Diffraction Measurements
(1970-01-01)
Tu-Ngoc Lam
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Wu, Szu-Chien
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Chae, Hobyung
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Chen, Shi-Wei
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Jain, Jayant
Gray cast iron comprises alpha-Fe, Fe3C and graphite with their different anisotropies in terms of structure and mechanical behavior. We perform two different deformation paths as tension-compression and compression-tension on bulk gray iron to capture the stress partitioning. Usingin situneutron diffraction, the composite-like deformation behaviors of alpha-Fe and Fe3C are revealed simultaneously. Within the elastic deformation stage, both deformation paths do not cause load transfer. However, when the applied compressive stress exceeds 300 MPa, there is a clear load sharing in both paths. From microscopic examinations, the debonding between matrix and graphite is clarified.
Plastic anisotropy and deformation-induced phase transformation of additive manufactured stainless steel
(2019-08-05)
Chae, Hobyung
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Huang, E-Wen
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Jain, Jayant
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Wang, Huamiao
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Woo, Wanchuck
Plastic anisotropy and deformation-induced phase transformation of additively manufactured (AM) stainless steels were investigated via in-situ neutron diffraction, electron backscatter diffraction, metallography, and fractography. Two types of tensile specimens were manufactured: (1) One sample was vertically fabricated with its tensile axis parallel to the z-direction (AM-V), (2) The other sample was horizontally fabricated with its tensile axis perpendicular to the z-direction (AM-H). A commercial 15-5PH stainless steel (CA) was used for comparison. AM steel revealed enhanced yield strength, tensile strength, and uniform elongation over CA, which was mainly due to grain refinement and transformation induced plasticity (TRIP). Different onsets of strain nonlinearity between AM-V and AM-H were closely related to martensitic phase transformation. Stresses estimated from lattice strains measured by neutron diffraction matched well with the applied stress-strain curves. After plastic deformation, voids were formed and congregated near the solidified line where fine grains were populated. Higher dislocation density was observed in the fine grain zone, and lower density was shown in the relatively coarse grain zone. AM steels exhibited significant anisotropic fracture behavior in terms of loading direction. In contrast to isotropic failure for CA and AM-V, AM-H revealed anisotropic failure with elliptical formation of the fracture feature. The fracture surface of AM-H possessed many secondary cracks propagating perpendicular to the building direction. The occurrence of secondary cracks in AM-H resulted in rapid load drop during tensile loading after necking.
Quantitative evaluation of grain boundary sliding and its dependence on orientation and temperature in pure Zn
(2019-07-01)
Gokhale, Aditya
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Sarvesha, R.
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Huang, E-Wen
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Lee, Soo Yeol
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Prasad, Rajesh
In the present work, grain boundary sliding (GBS) has been studied for the grains exhibiting different orientations (for indentation parallel and perpendicular to < c > axis) at different temperatures (RT to 200 degrees C) using nanoindentation in pure Zn. Electron back scattered diffraction was utilized to determine the orientation of the indented grains and identify the deformation mechanism, whereas atomic force microscopy was utilized to systematically quantify the GBS. Results indicated that indentation perpendicular to < c > axis exhibits slip induced GBS, whereas the indentation parallel to < c > axis results in pure GBS. The amount of GBS was also found to be strongly dependent upon the orientation of the neighboring grain. Further, the contribution from GBS towards total stain was found to increase with an increase in temperature. (C) 2019 Elsevier B.V. All rights reserved.