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Suk Hoon Kang

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Papers by Suk Hoon Kang

Spray Deposition of Mechanically Alloyed F/M ODS Steel Powder

Archives of Metallurgy and Materials

Thermal/cold spray deposition were used for additive manufacture of oxide dispersion strengthened... more Thermal/cold spray deposition were used for additive manufacture of oxide dispersion strengthened (ODS) steel layers. Mechanically alloyed F/M ODS steel powders (Fe(bal.)-10Cr-1Mo-0.25Ti-0.35Y2O3 in wt.%) were sprayed by a high velocity oxygen fuel (HVOF) and cold spray methods. HVOF, as a thermal method, was used for manufacturing a 1 mm-thick ODS steel layer with a ~95% density. The source to objective distance (SOD) and feeding rate were controlled to achieve sound manufacturing. Y 2 Ti 2 O 7 nano-particles were preserved in the HVOF sprayed layer; however, unexpected Cr 2 O 3 phases were frequently observed at the boundary area of the powders. A cold spray was used for manufacturing the Cr 2 O 3-free layer and showed great feasibility. The density and yield of the cold spray were roughly 80% and 45%, respectively. The softening of ODS powders before the cold spray was conducted using a tube furnace of up to 1200°C. Microstructural characteristics of the cold sprayed layer were investigated by electron back-scattered diffraction (EBSD), the uniformity of deformation amount inside powders was observed.

format_quoteHardness decreased by nearly half after softening at 1200°C, significantly impacting deposition efficiency of ODS powders.format_quote

Microstructure Evolution of 15Cr ODS Steel by a Simple Torsion Test

Journal of Korean Powder Metallurgy Institute, 2014

15Cr-1Mo base oxide dispersion strengthened (ODS) steel which is considered to be as a promising ... more 15Cr-1Mo base oxide dispersion strengthened (ODS) steel which is considered to be as a promising candidate for high-temperature components in nuclear fusion and fission systems because of its excellent high temperature strength, corrosion and radiation resistance was fabricated by using mechanical alloying, hot isostatic pressing and hot rolling. Torsion tests were performed at room temperature, leading to two different shear strain routes in the forward and reverse directions. In this study, microstructure evolution of the ODS steel during simple shearing was investigated. Fine grained microstructure and a cell structure of dislocation with low angle boundaries were characterized with shear strain in the shear deformed region by electron backscattered diffraction (EBSD). Grain refinement with shear strain resulted in an increase in hardness. After the forward-reverse torsion, the hardness value was measured to be higher than that of the forward torsion only with an identical shear strain amount, suggesting that new dislocation cell structures inside the grain were generated, thus resulting in a larger strengthening of the steel.

On the coherency of Y2Ti2O7 particles with austenitic matrix of oxide dispersion strengthened steel

Acta Materialia, 2015

Coherency and orientation relationship of nano-sized Y 2 Ti 2 O 7 particles with an austenitic ma... more Coherency and orientation relationship of nano-sized Y 2 Ti 2 O 7 particles with an austenitic matrix of oxide dispersion strengthened steel was investigated using selected area diffraction contrast techniques and high resolution transmission electron microscopy. It was revealed that over 95% of the Y 2 Ti 2 O 7 particles (3-10 nm in diameter) are semi-coherent with the austenitic matrix. Perfectly matched planes, which produce no-contrast lines under proper two-beam conditions in transmission electron microscopy (TEM), were obtained across the oxide/matrix interface between parallel planes of 2 2 0 À Á Y2Ti2O7 == 2 0 0 ð Þ Matrix , and 3 3 1 À Á Y2Ti2O7 == 0 2 2 À Á Matrix. A single no-contrast line and multiple no-contrast lines under different active g-vectors were observed and discussed. The lattice distortion in the matrix around the Y 2 Ti 2 O 7 particles was determined using the diffraction contrast method under TEM and through X-ray diffraction analyses, which revealed good agreement. A decrease in the inter-planar spacing of up to 7.5% was detected in 0 2 2 À Á Matrix planes owing to the misfit strain at the oxide/matrix interface.

Effects of alloying elements and heat treatments on mechanical properties of Korean reduced-activation ferritic–martensitic steel

Journal of Nuclear Materials, 2014

In this paper, the effects of alloying elements Ti and N, different heat treatments and permeatio... more In this paper, the effects of alloying elements Ti and N, different heat treatments and permeation temperature on hydrogen diffusion in SCRAM steels were investigated. Devanathan-Stachurshi electrochemical hydrogen permeation technique was used to determine the hydrogen diffusivity. The results show that increasing the content of Ti and N can decrease the hydrogen diffusion coefficient of SCRAM steels. Compared with the traditional quenching and tempering heat treatment process, the process including an intermediate hold can refine the M23C6 phase, increase the volume fraction of MX phase but coarsen the martensitic lath. The twice quenching and tempering heat treatment process can not only refine the martensitic lath and M23C6 phase, but also increase the volume fraction of MX phase, resulting in a decrease of hydrogen diffusivity. The hydrogen permeation steady-state current density and the hydrogen diffusivity increase with the rise of permeation temperature. The temperature dependence of hydrogen diffusion coefficient conforms with the Arrhenius relationship. And the activation energy for hydrogen diffusion of two SCRAM steels with different heat treatments was determined.

format_quoteHydrogen permeation tests showed that increasing Ti content in SCRAM steels correlated with decreased hydrogen diffusion coefficients under controlled conditions.format_quote

Current Status and Future Prospective of Advanced Radiation Resistant Oxide Dispersion Strengthened Steel (ARROS) Development for Nuclear Reactor System Applications

Nuclear Engineering and Technology, 2016

As one of the Gen-IV nuclear energy systems, a sodium-cooled fast reactor (SFR) is being develope... more As one of the Gen-IV nuclear energy systems, a sodium-cooled fast reactor (SFR) is being developed at the Korea Atomic Energy Research Institute (KAERI). As a long-term national research project, advanced radiation resistant ODS steel (ARROS) is being developed as an in-core fuel cladding tube material for a SFR in the future. In this paper, the current status of the ARROS development is reviewed and the future prospective is discussed.

Microtexture and Material Flow Analysis on Friction Stir Welded Materials

Fracture Resistances of Y2O3 Particle Dispersion Strengthened 9Cr Steel at Room Temperature and High Temperatures

Korean Journal of Metals and Materials, 2012

The fracture resistance and tensile properties of Y 2 O 3 oxide dispersion strengthened steel con... more The fracture resistance and tensile properties of Y 2 O 3 oxide dispersion strengthened steel containing 9 wt% Cr (9Cr-ODS) were measured at various temperatures up to 700 o C. The fracture characteristics were compared with those of commercial E911 ferritic/martensitic steel. The strength of 9Cr-ODS was at least 30% higher than that of E911 steel at the test temperatures below 500 o C. The strength difference between the two materials was almost diminished at 700 o C. 9Cr-ODS showed cleavage fracture behavior at room temperature and unstable crack growth behaviors at 300 o C and 500 o C. The J-R fracture resistance of 9Cr-ODS was much lower than that of E911 steel at all temperatures. It was deduced that the coarse Cr 2 O 3 particles that were formed during the alloying process provided the crack initiation sites of cleavage fracture in 9Cr-ODS.

INFLUENCE OF MECHANICAL ALLOYING ATMOSPHERES ON THE MICROSTRUCTURES AND MECHANICAL PROPERTIES OF 15Cr ODS STEELS

Nuclear Engineering and Technology, 2014

format_quoteODS ferritic steels were consolidated through advanced processes, revealing significant links between gas atmospheres and performance metrics.format_quote

TEM & EBSD Study on Deformation Behavior of High Nitrogen Austenitic Fe-18Cr-18Mn-2Mo-0.9N Stainless Steel

Solid State Phenomena, 2007

Deformation behavior of high nitrogen austenitic Fe-18Cr-18Mn-2Mo-0.9N stainless steel was invest... more Deformation behavior of high nitrogen austenitic Fe-18Cr-18Mn-2Mo-0.9N stainless steel was investigated utilizing electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). During deformation, the <110> grains rotated and the trace of these grains moved towards into the dodecahedral plane (the line connecting (001) and (111) planes). Misorientation mapping in EBSD showed that the special boundaries (almost Σ3) gradually diminished whereas the low-angle boundaries were developed. TEM observation showed that (i) the low-angle boundaries developed corresponded to the deformation twinning with {111}<112> component, (ii) the deformation twinning showed the strong orientation dependence relative to tensile axis, and (iii) the deformed microstructure was characterized by extended stacking faults, planar dislocation array in low strain regime, and by well-developed deformation twinning in high strain region, respectively.

Microstructural Evaluation and High Temperature Mechanical Properties of Ni-22Cr-18Fe-9Mo ODS Alloy

Journal of Korean Powder Metallurgy Institute, 2011

Electrochemical properties of nanosized Li-rich layered oxide as positive electrode materials for Li-Ion batteries

A nanosized Li-rich layered oxide/carbon composite material is successfully prepared by simple ba... more A nanosized Li-rich layered oxide/carbon composite material is successfully prepared by simple ball milling pulverization of microsphere-shaped Li-rich layered oxide materials with conductive carbon. The nanosized Li-rich layered oxide/carbon composite electrode exhibits a high 1st discharge capacity of 250 mAh g 21 with an excellent rate capability at high current density. The composite also reduces the internal resistance from oxygen release during the electrochemical activation of Li 2 MnO 3. The improvement in the electrochemical performance of nanosized Li-rich layered oxide/carbon composite materials primarily occurs because the nanosized particles facilitate the diffusion of Li within the structure and provide innumerable reaction sites with lithium. Furthermore, the electronic conductivity of the active material is effectively enhanced by the carbon coating on the particles. In addition, unique effects of ball milling on the electrochemical properties of the Li-rich layered oxides are observed: (i) pre-activation of the Li 2 MnO 3 component and (ii) gradual electrochemical activation under 4.3 V during cycling. Adverse effects on the electrochemical stability of the nanosized Li-rich layered oxide are also discussed, and these adverse effects mainly arise due to (i) the structural deformation of hexagonal ordering, (ii) the growth of the spinel component and (iii) the insufficient formation of a protective NiF 2 layer on the surface of the active material.

Fatigue measurement system designed for a chalcogenide-based device using a homemade heater tip

Review of Scientific Instruments, 2008

A fatigue measurement system is designed using a homemade tungsten (W) heater tip. This system is... more A fatigue measurement system is designed using a homemade tungsten (W) heater tip. This system is composed of a pulse generator and an atomic force microscope with the W heater tip attached. Also included are a parameter analyzer and control devices. The entire measurement process is controlled by a designed program without communication errors. Additionally, a process to fabricate the sharp W heater tip that applies an electrical pulse and evaluates the electrical properties is introduced. The analysis of the tip, carried out by scanning electron microscopy and electron backscattering diffraction, shows that the tip has great thermomechanical stability. Using this fatigue measurement system, the resistance of the Ge2Sb2Te5 (GST) cell was successfully measured as a function of the number of set/reset cycles. The specific area (both program area and failure area) was easily observed. It is expected that the expansion of GST is a source of information regarding the fatigue of a GST cell.

format_quoteThe integration of Joule heating via a W heater tip allows controlled phase transitions in GST, key for non-volatile memory applications.format_quote

$Research paper thumbnail of Electron Backscattered Diffraction Analysis of Eutectic Solidification in a Continuous Cast Aluminum Alloy Billet$

Electron Backscattered Diffraction Analysis of Eutectic Solidification in a Continuous Cast Aluminum Alloy Billet

Materials and Manufacturing Processes, 2014

ABSTRACT Eutectic silicon structure was modified by fine-grained structural material as the maste... more ABSTRACT Eutectic silicon structure was modified by fine-grained structural material as the master alloy. An investigation of the crystallographic orientations of eutectic colonies has been carried out by electron backscatter diffraction. The morphologies of eutectic silicon alter from lamellar to fibrous shape after adding 30% fine-grained structural material master alloy. The coupling relationship of eutectic colonies becomes stronger in modified aluminum–silicon alloys. Furthermore, the misorientation angles in the eutectic colony change from high angle grain boundaries (≥15°) to low angle grain boundaries (≤5°). The misorientation angles inside eutectic silicon decrease from 60° to low angle grain boundaries (≤5°). The primary α-aluminum dendrite and neighboring eutectic aluminum have almost the same crystallographic orientation in modified aluminum–silicon alloys.

Characterization of the crystallographic microstructure of the stress-induced void in Cu interconnects

Applied Physics Letters, 2008

Stepwise cross-sectional crystallographic measurement was performed on the stress-induced void (S... more Stepwise cross-sectional crystallographic measurement was performed on the stress-induced void (SIV) of copper interconnect and it was possible to investigate the three-dimensional crystallographic structures near the submicron scale void. The void mainly happened at a triple junction of grain boundaries and there were at least two grains with high biaxial elastic modulus near the triple junction. The preferred site for the SIV could well be understood by considering the elastic anisotropy of each grain and the grain boundary type.

Observations on the Failure Behavior in a Diamond-Like Carbon Coated Nitinol Vascular Stent under Cyclic Loading

We investigated a failure behavior of diamond-like carbon (DLC) coated metallic vascular stent un... more We investigated a failure behavior of diamond-like carbon (DLC) coated metallic vascular stent under cyclic loading. We employed cyclic loading of compression and tension on a Vshaped stent unit coated with DLC thin film using a screw-driven tensile tester. It was observed that channel cracking and delamination of DLC film occurred intensively in the regions subject to the tensile strain during cyclic loading. We investigated the pre-cleaning effect on the interfacial delamination behavior by the cross-sectional analysis of the fractured region using a dual beam FIB/SEM system.

Three-dimensional numerical and experimental investigation on friction stir welding processes of ferritic stainless steel

Acta Materialia, 2013

This paper presents transient simulations and experimental studies of the ignition process of the... more This paper presents transient simulations and experimental studies of the ignition process of the hybrid rocket motors (HRMs) using 90% hydrogen peroxide (HP) as the oxidizer and polymethyl methacrylate (PMMA) and Polyethylene (PE) as fuels. A fluid-solid coupling numerically method is established based on the conserved form of the three-dimensional unsteady Navier-Stokes (N-S) equations, considering gas fluid with chemical reactions and heat transfer between the fluid and solid region. Experiments are subsequently conducted using high-speed camera to record the ignition process. The flame propagation, chamber pressurizing process and average fuel regression rate of the numerical simulation results show good agreement with the experimental ones, which demonstrates the validity of the simulations in this study. The results also indicate that the flame propagation time is mainly affected by fluid dynamics and it increases with an increasing grain port area. The chamber pressurizing process begins when the flame propagation completes in the grain port. Furthermore, the chamber pressurizing time is about 4 times longer than the time of flame propagation.

$Research paper thumbnail of A Quantitative Evaluation of Microstructure by Electron Back-Scattered Diffraction Pattern Quality Variations$

A Quantitative Evaluation of Microstructure by Electron Back-Scattered Diffraction Pattern Quality Variations

Microscopy and Microanalysis, 2013

Band contrast (BC) is a qualitative measure of electron back-scattered diffraction (EBSD), which ... more Band contrast (BC) is a qualitative measure of electron back-scattered diffraction (EBSD), which is derived from the intensity of the Kikuchi bands. The BC is dependent upon several factors including scanning electron microscope measurement parameters, EBSD camera setup, and the specimen itself (lattice defect and grain orientation). In this study, the effective factors for BC variations and the feasibility of using BC variations for the quantification of microstructure evolutions have been investigated. In addition, the effects of the lattice defect and the grain orientation on the BC variations are studied. Next, a shear-deformed microstructure of 316L stainless steel, which contains nanosized grains and a large portion of twin boundaries, is revealed by BC map and histogram. Recovery and recrystallization of shear-deformed 316L stainless steel are displayed by BC variations during isothermal annealing at 700 and 800°C, respectively. It is observed that the BC turns bright as the ...

$Research paper thumbnail of 3D Crystalline Structures of Stress Induced Voiding in Cu Interconnects by Focused Ion Beam and Electron Backscattered Diffraction$

3D Crystalline Structures of Stress Induced Voiding in Cu Interconnects by Focused Ion Beam and Electron Backscattered Diffraction

2006 International Interconnect Technology Conference, 2006

The planar and cross-sectional crystalline analyses were performed on the stress induced voiding ... more The planar and cross-sectional crystalline analyses were performed on the stress induced voiding (SIV). The SIV was initiated at the triple junction of grain boundaries, not at the junction of twin and grain boundaries. The void grew preferentially in one of the grains joining at the triple junction. From stress calculation based on the measured crystalline structure, the voided grain

페라이트/마르텐사이트계 산화물 분산강화 합금의 미세조직과 인장특성에 미치는 Cr, Mo, Al, Zr, Y2O3의 영향

Korean Journal of Metals and Materials, 2014

To develop an advanced ODS alloy for core structural materials for next-generation nuclear reacto... more To develop an advanced ODS alloy for core structural materials for next-generation nuclear reactor system applications, effects of alloying elements such as Cr, Mo, Al, Zr and Y2O3 on microstructures and tensile properties of ODS ferritic/martensitic alloys were investigated. The ODS alloys were fabricated by mechanical alloying, hot isostatic pressing, and hot rolling processes. The Cr concentration revealed little effect on the tensile strength, but it affected the grain morphology as a result of phase transformation. Mo acted to increase the tensile strength at an elevated temperature. Both grain and oxide particle sizes were significantly coarsened by Al addition. These enlargements led to a decrease in tensile strength but improved the elongation. Minor addition of Zr enhanced the tensile strength, and an increase of Y2O3 addition deteriorated the elongation. These results could be very useful in optimizing the alloying element concentration of ODS alloys with superior out-of-pile mechanical properties.

Relationship between formability and microstructure of Al alloy sheet locally modified by friction stir processing

Scripta Materialia, 2007

ABSTRACT