
Jeong Min ParkKorea Institute of Materials Science · Department of 3D Printing Materials
Jeong Min Park
Ph.D.
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75
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Introduction
Currently working as a senior researcher at the Department of 3D Printing Materials, Korea Institute of Materials Science (KIMS).
E-mail: jmpark@kims.re.kr
Publications
Publications (75)
CoCrFeMnNi high-entropy alloys containing 1 at% carbon (C-HEAs) were additively manufactured using selective laser melting (SLM). Superior tensile properties of the as-built C-HEA (to previously reported ones) were achieved by utilizing multiple strengthening mechanisms (i.e. solid solution, grain refinement, dislocation density, and nano-precipita...
Selective laser melting (SLM) offers unprecedented advantages in the fabrication of metals and alloys with complex geometry and unique microstructural features with hierarchical heterogeneity. The SLM process also induces a unique cell structure with high dislocation density and solute segregation at cell boundaries. Here, we propose an innovative...
The concept of cell boundary (CB) engineering was proposed to explore the potential benefits of segregation engineering in obtaining superior mechanical properties in materials printed via laser powder bed fusion (LPBF). Mo-doped and Mo-free ferrous medium-entropy alloys (FeMEAs) were additively manufactured using LPBF. A high density of dislocatio...
Additive manufacturing makes it possible to improve the mechanical properties of alloys through segregation engineering of specific alloying elements into the dislocation cell structure. In this study, we investigated the mechanical and microstructural characteristics of CoNi-based medium-entropy alloys (MEAs), including the refractory alloying ele...
The AlSi10Mg alloy has garnered significant attention for its application in laser powder bed fusion (L-PBF), due to its lightweight properties and good printability using L-PBF. However, the low production speed of the L-PBF process is the main bottleneck in the industrial commercialization of L-PBF AlSi10Mg alloy parts. Furthermore, while L-PBF A...
Crack-free Al–Zn–Mg–Cu alloy, processed by laser powder bed fusion, displays a characteristic microstructure comprising fine equiaxed grains (EGs) and coarse columnar grains (CGs). Notably, the CGs show a high hardness compared to EGs due to the high density of in-situ precipitates. Analysis of mechanical properties takes into account the precipita...
In order to predict the process window of laser powder bed fusion (LPBF) for printing metallic components, the calculation of volumetric energy density (VED) has been widely calculated for controlling process parameters. However, because it is assumed that the process parameters contribute equally to heat input, the VED still has limitation for pre...
The emergence of ferrous-medium entropy alloys (FeMEAs) with excellent tensile properties represents a potential direction for designing alloys based on metastable engineering. In this study, an FeMEA is successfully fabricated using laser powder bed fusion (LPBF), a metal additive manufacturing technology. Tensile tests are conducted on the LPBF-p...
H13 tool steel was additively manufactured by selective laser melting (SLM). The sample printed at a higher laser scan speed exhibited higher strength and ductility than those of the sample printed at a lower speed. The samples were repeatedly exposed to a massive heat input during the SLM. The in-situ tempering effect was applied to the sample; th...
Although the Ti-6Al-4V alloy has been used in the aircraft industry owing to its excellent mechanical properties and low density, the low formability of the alloy hinders broadening its applications. Recently, laser-powder bed fusion (L-PBF) has become a novel process for overcoming the limitations of the alloy (i.e., low formability), owing to the...
This study investigated cracking phenomena in 316L stainless steel (SS316L) and Inconel 718 (IN718) composition-graded material (CGM) additively manufactured by the direct energy deposition (DED) process. In order to prevent cracking in the CGM, thermodynamic analysis was performed to avoid the critical concentration for crack formation. Based on t...
Cell structures decorated with Si precipitates are key microstructures that endow AlSi10Mg alloys produced by laser powder bed fusion (LPBF) with excellent mechanical properties. This study investigated the effect of heat treatment on the cell structure and properties of LPBFed AlSi10Mg alloys. Heat-treatment was performed within the temperature ra...
Because magnets fabricated using Nd-Fe-B exhibit excellent magnetic properties, this novel material is used in various high-tech industries. However, because of the brittleness and low formability of Nd-Fe-B magnets, the design freedom of shapes for improving the performance is limited based on conventional tooling and postprocessing. Laser-powder...
Harmonic structured material (HSM) of coarse-grained core and fine-grained shell microstructure in SS304L was designed using a three-dimensional numerical model developed to simulate the unique deformation behavior of heterostructured materials. Hetero-deformation induced (HDI) strengthening feature was implemented into the model by considering the...
Impact toughness at ambient and cryogenic temperatures was investigated with systematic fracture analyses for CuFeMn and Al15(CuFeMn)85 (at%) immiscible medium-entropy alloys. These two types of alloys exhibited different impact toughness behavior at different temperatures, while exhibiting higher impact toughness values than those of dual-phase st...
Developing metal additive parts with a synergy in strength and ductility is a demanding need for many critical applications. Recently, gradient structures have been of research interest as it facilitates intrinsic synergetic strengthening. In the current work, gradient microstructures are obtained on laser-powder bed fusion processed (LPBF) CoCrFeM...
Recently, direct energy deposition (DED) has been attracting considerable attention in metal additive manufacturing due to its capability of producing multi-materials and composition gradient materials with a high degree of geometrical design freedom and relatively high productivity compared to powder bed fusion processing. In this study, layered m...
The microstructure and mechanical properties of AlSi10Mg alloy fabricated by selective laser melting were systematically investigated in this study. Substantial hardening of this alloy was achieved by aging heat treatment. The alloy exhibits an excellent combination of strength and ductility, attributed to its fine cellular structure with nanoscale...
Process optimization of additively manufactured Ti–6Al–4V alloy is an important aspect of the production of engineered, high-performance parts for the aerospace and medical industries. In this study, the microstructural evolution and mechanical properties of direct energy deposition processed Ti–6Al–4V alloy were investigated using different proces...
Liquid metal dealloying (LMD) has recently attracted significant attention. Because the LMD process enables the production of three-dimensional (3D) interconnected non-noble metallic materials. In addition, the metallic melt medium is useful for the development of heterostructure (HS) metal-metal composites. However, the solidified liquid metal pha...
A breakthrough in the strength and ductility trade-off is crucial for the development of advanced metallic materials. Herein, we present a novel heterostructured composite composed of immiscible magnesium (Mg) and ferrochrome (FeCr) with a 3D interconnected morphology and synthesized by liquid metal dealloying. Soft Mg and hard FeCr zones mutually...
In this study, we quantitatively investigated the effect of heat treatment on microstructural evolution and mechanical properties in the selective laser melting (SLM) processed 1%C-CoCrFeMnNi high-entropy alloy (C-HEA). The addition of carbon atoms resulted in a nano-sized Cr23C6 carbide phase in the SLM-processed C-HEA, significantly retarding the...
Rapid melting and solidification cycles during laser-based additive manufacturing create non-equilibrium microstructures in stainless steels (SSs) including atomic segregation-mediated ultrafine δ-ferrite, in contrast to coarse δ-ferrite in typical casting-produced SSs. The formation of metastable ultrafine δ-ferrite in additively manufactured SSs...
In this work, laser welding of a rolled CoCrFeMnNi high entropy alloy to 316 stainless steel was performed. Defect-free joints were obtained. The microstructure evolution across the welded joints was assessed and rationalized by coupling electron microscopy, high energy synchrotron X-ray diffraction, mechanical property evaluation, and thermodynami...
In this study, quasi-static tensile properties of Fe60Co15Ni15Cr10 (at%) ferrous medium-entropy alloy at 298 K and 77 K were investigated in terms of thermally-activated deformation mechanism. Relatively high strain rate sensitivity and low activation volume were estimated using strain rate jump tests at 77 K where deformation-induced martensitic t...
The digitized format of microstructures, or digital microstructures, plays a crucial role in modern-day materials research. Unfortunately, the acquisition of digital microstructures through experimental means can be unsuccessful in delivering sufficient resolution that is necessary to capture all relevant geometric features of the microstructures....
A strategy to improve the tensile properties of Co 17.5 Cr 12.5 Fe 55 Ni 10 Mo 5 (at%) medium-entropy alloy through high-pressure torsion and subsequent annealing is presented in this work. Microstructural study revealed that the high-pressure torsion process led to the formation of fine grains (≤~1 μm) and profuse nano-scale Mo-rich μ-phase precip...
An equiatomic VCoNi medium-entropy alloy possesses high sensitivity to grain-boundary strengthening, achieved by severe lattice distortions. Its ultrafine-grain structure enables 1.5 Gigapascal yield strength even for the fully recrystallized alloy with a single face-centered cubic structure. The high density of grain boundaries also generates high...
We investigated the stretch-flangeability of CoCrFeMnNi high-entropy alloy (HEA) in comparison with other face-centered cubic alloys (304 stainless steel and twinning-induced plasticity steel). The hole-expansion ratio of the HEA was superior to those of the other alloys, attributed to fewer vulnerable sites for crack-initiation and the resulting h...
The rapid melting and solidification cycle in additive manufacturing creates a non-equilibrium environment that induces metastable microstructures. These metastable microstructures include solute heterogeneity, dislocation cell structure and nano-sized precipitation, which contributes to the strength of additively manufactured alloys. Because the p...
A unique heterogeneous microstructure was generated in the tungsten carbide-cobalt (WC-Co) composite additively-manufactured by selective laser melting (SLM). In this work, the effect of microstructural heterogeneity on mechanical properties and crack propagation in SLM-processed WC-Co is investigated. The strength and strain calculation model is c...
Here, novel medium-entropy alloys with chemical compositions of Co17.5Cr12.5Fe55Ni10Mo4C1 and Co17.5Cr12.5Fe55Ni10Mo3C2 (at%) exhibiting excellent tensile properties at both room and liquid nitrogen temperatures have been developed. Precipitation of carbides changes the chemical composition and phase stability of the matrix, resulting in the contro...
In this work, the mechanical properties and microstructural evolution of a recently developed immiscible medium-entropy alloy (Al15(CuFeMn)85, at%) at 77 K were investigated. Nanoscale deformation twinning was observed in both Cu-rich and Fe-rich grains. Twin-mediated martensitic transformation from Cu-rich β1 phase to β1’ martensite was occurred d...
The current work reports nano-precipitation and exceptional combination of high strength and ductility in a Cu-13Sn alloy, fabricated by selective laser melting (SLM). The SLM samples revealed competitive unidirectional columnar grains with a fine cellular structure (∼600 nm) having Cu-rich spherical nano-precipitates (∼3 nm), and δ-phase (Cu41Sn11...
The friction-stir weld (FSW) was investigated based on the relationship between microstructural and mechanical properties at room and cryogenic temperatures for rolled and cast Co0.2Cr0.2Fe0.2Mn0.2Ni0.2 high entropy alloys (HEAs). The rolled and cast HEA welds exhibited good weldability without welding defects. The grain size (GS) of the stir zone...
High entropy alloys have emerged as novel engineering alloys with remarkable mechanical properties in a wide range of temperatures. Among the several high entropy alloys that were already described, the equiatomic CrMnFeCoNi alloy is the most studied one. In this work, gas tungsten arc welding of as-rolled CrMnFeCoNi high entropy alloy sheets was p...
Here, a new strategy for designing heterogeneous medium-entropy alloys with light-weight and excellent mechanical properties is proposed. Alx(CuFeMn)100-x (x = 0, 7.5, and 15 at%) alloys were developed by utilizing the immiscible nature of Cu-Fe alloys. The microstructures of the alloys show phase separation into Cu-rich and Fe-rich regions, and th...
Heterogeneous structured materials achieve a combination of high strength and extreme ductility due to synergetic strengthening driven by conditions in the interfacial region. Although the origin of synergetic strengthening has been revealed to be strain incompatibility in the interfacial region, the effect of the strength difference between hard a...
Observations based on either side of experiment or modeling often have difficulties in understanding microstructural and mechanical evolutions during deformation, and in application to the macroscopic behavior of materials. In the present study, an integrated experimental-numerical analysis on ferrous medium-entropy alloy (FMEA) was conducted to un...
Hydrogen embrittlement, which originates from hydrogen localization in internal defects (i.e., grain boundaries, twins, and interface), induces both decohesion and strain localization in high- strength steels. Such embrittlement is a critical issue when attempting to prolong the material life in an actual environment. Therefore, microstructural des...
Rapid melting and solidification cycle during additive manufacturing provides a non-equilibrium environment that generates a large amount of internal defects, including dislocations, precipitations, and solute heterogeneity. These internal defects not only enhance the strength of materials by interacting with mobile dislocations but also reduce duc...
Strain-rate dependence in face centered cubic high entropy alloys still remains controversial despite extensive efforts on this topic. Strain-rate sensitivity reflects underlying thermally-activated deformation and the controversy boils down to the deformation mechanism. There has been disagreement even on the experimental values of the strain-rate...
We engineered an Al0.3CoCrNi medium-entropy alloy with heterogeneous grain structure and nanoscale precipitation through thermo-mechanical processing route, with an aim to achieve a remarkable combination of cryogenic yield strength and ductility. The alloy exhibits an exceptional combination of high cryogenic yield strength of ∼1.1 GPa and high un...
The enhancement of strength in materials by conventional strengthening mechanism is always accompanied by loss of ductility due to the reduced strain hardenability, leading to a strength–ductility trade-off. In this paper, we engineered Al0.3CoCrNi medium-entropy alloy to contain multi-phase hierarchical microstructure and demonstrated a high yield...
Copper (Cu) acts as a strong face-centered cubic (FCC) stabilizer as well as an effective element lowering the melting point in FCC-structured high-entropy alloy (HEA) systems. The addition of Cu can reduce the alloy processing temperature; however, there are no studies on the formation of single FCC phase in Cu-added HEAs yet. In this study, a Co1...
A physics-based constitutive model of porous materials is proposed to enhance the accuracy of numerical analysis in die/isostatic compaction. The correlation between the yield function and equivalent work equation was derived, and the numerical integration method was modified with the correlation. It is found that the apparent work of porous materi...
Synergetic strengthening induced by plastic strain incompatibility at the interface, and the resulting extra geometrically necessary dislocations (GNDs) generated during plastic deformation, were investigated to understand the origin of extra strength in heterogeneous structured (HS) materials. The mechanism of extra GND generation in twinning-indu...
Phase stress evolution of face-centered cubic (FCC) and deformation-induced body-centered cubic (BCC) phases was measured in recently developed ferrous medium-entropy alloy. This was done during tensile deformation at −137 °C using in situ neutron diffraction measurement for the quantitative interpretation of the role of martensitic transformation...
Dual-phase Al0.5CoCrFeMnNi high-entropy alloy consisted of face-centered cubic (FCC) and body-centered cubic (BCC) phases exhibited enhancement of both strength and strain hardening ability at 77 K. It resulted from back stress hardening in high work hardening due to large strength difference of two constituent phases with decreasing temperature.
Selective laser melting (SLM), a type of additive manufacturing (AM) technology, leads a global manufacturing trend by enabling the design of geometrically complex products with topology optimization for optimized performance. Using this method, three-dimensional (3D) computer-aided design (CAD) data components can be built up directly in a layer-b...
Non-equiatomic Co17.5Cr12.5Fe55Ni10Mo5 (Mo5) and Co18Cr12.5Fe55Ni7Mo7.5 (Mo7.5) medium-entropy alloys were synthesized by vacuum induction melting, cold rolling, and subsequent annealing treatment at various temperatures (900–1200 °C) and they were investigated to exploit the precipitation strengthening in addition to solid solution strengthening o...
In the present study, V10Cr15Mn5Fe35Co10Ni25 (at%) high-entropy alloy (HEA) of a single phase face-centered cubic structure with various grain sizes was fabricated. The influences of grain size on the work-hardening behavior and deformation mechanisms were investigated. The fine-grained and coarse-grained samples showed different work hardening beh...
Annealing of severely plastic deformed materials is expected to produce a good combination of strength and ductility, which has been widely demonstrated in conventional materials. In the present study, high-pressure torsion processed CoCrNi medium entropy alloy consisting of a single face-centered cubic (FCC) phase with a grain size of ~50 nm was s...
A nanocrystalline CoCrNi alloy of ~50 nm grain size with the ultra-high ultimate tensile strength of ~2.2 GPa and fracture strain of ~9% was fabricated using high-pressure torsion. The presence of high density of nano-twins, stacking faults, dislocations, and nano-grains is attributed to the superior mechanical properties.
In this work, the mechanical characteristics and microstructural evolution of Al0.5CoCrFeMnNi high-entropy alloy (HEA) were studied after annealing at various temperatures (1000, 1100, and 1200 °C). X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy analyses were performed to reveal the phase and microstructural var...
In the present work, a solid solution strengthening effect in high-entropy alloys (HEAs) was studied by investigating mechanical characteristics of single crystalline CoCrFeMnNi HEA and a corresponding model was developed. (100) and (110) oriented single crystals of the CoCrFeMnNi alloy were grown and their single crystallinity was identified using...
In this work, the effects of strain rate on mechanical deformation and microstructural evolution of CoCrFeMnNi high-entropy alloy (HEA) under quasi-static and dynamic compression were investigated. The HEA exhibited high strain-rate sensitivity values (m = 0.028) of yield strength under quasi-static conditions. In particular, due to the viscous dra...
본 연구에서는 진공 유도 용해 (Vacuum induction melting)를 통해 제조 된 단상의 FCC 구조를 갖는 CoCrFeMnNi 고엔트로피합금에 대한 준정적 및 동적 압축 시험을 시행하여 변형률 속도에 따른 미세조직 및 기계적 성질 변화에 대해 탐구하였다. 실험 결과, 해당 합금은 준정적 및 동적 압축 변형 하에서 높은 변형률속도민감도 (Strain rate sensitivity)를 나타내었다. 이 때, 변형률속도민감도는 동적 압축에서의 값 (m ~ 0.25-31)이 준정적 압축에서의 값 (m ~ 0.028)보다 10배 큰 것을 확인할 수 있는데, 이것은 동적 변형 시 전위 이동에서의 포논 드래그 (Phon...