Yong Bum Choi

Hiroshima University | HU · Graduate School of Advanced Science and Engineering

In this study, polyvinyl alcohol (PVA) - polytetrafluoroethylene (PTFE) - vapor grown carbon fiber (VGCF) sheets are fabricated as a new paper-like thermal interface material (TIM), which is a potential substitute for traditional TIMs. Two types of PVA-PTFE-VGCF sheets were fabricated by using 120nm and 300nm PTFE particles. The microstructure show...

Titanium matrix composites (TMCs) with TiC reinforcements were fabricated by an in-situ method that evolves pure titanium foils (thick: 100 μm) and graphite powder sheets by spark plasma sintering. 20 μm thick graphite powder sheets with PVA (polyvinyl alcohol) were fabricated as carbon resources. The effects of different sintering temperatures and...

The conventional manufacturing process of fiber-reinforced metal matrix composites via liquid infiltration processes, preform manufacturing using inorganic binders is essential. However, the procedure involves binder sintering, which requires high energy and long operating times. A new fabrication process without preform manufacturing is proposed t...

A new fabrication process without preform manufacturing has been developed for carbon short fiber (CSF) reinforced various aluminum matrix composites. And their mechanical and thermal properties were evaluated. Electroless Ni plating was conducted on the CSF for improving wettability between the carbon fiber (CF) and aluminum. It was confirmed that...

Conventional manufacturing process of fiber reinforced metal matrix composites via liquid infiltration processes, preform manufacturing using inorganic binders is essential. However, the procedure involves binder sintering, which requires high energy and long operating times. A new fabrication process without preform manufacturing is proposed to fa...

Polyvinyl alcohol (PVA)-based carbon nanofiber (CNF) sheets are fabricated as an innovative thermal interface material (TIM), which is a potential substitute for traditional TIMs. Five types of PVA-based CNF sheets were fabricated at different mass ratios of PVA:vapor-grown carbon fiber (VGCF) (1:0.100, 1:0.070, 1:0.050, 1:0.030, 1:0.025). The thic...

Interfacial thermal resistance of Al-AlN composites was evaluated by comparing the measured thermal conductivity and the simulated thermal conductivity. Al-10vol.%AlN and Al-20vol.%AlN composites were fabricated by spark plasma sintering. Effective thermal conductivity was measured with the steady state thermal conductivity measuring device. Effect...

To investigate the influence of the angle of graphite on thermal conductivity and thermal expansion, the thermal properties of graphite reinforce Cu matrix composite was calculated with a simulation code which can take account of the angle of graphite at cross-section face. In this research, the orientation of graphite tends to be distributed paral...

The effective thermal conductivity (ETC) of graphite flake (GF)/Al composites is significantly influenced by the anisotropic thermal conductivity of GFs and the interfacial thermal resistance between both components. A two-dimensional (2D) image-based simulation was used in this study to investigate the effect of both the orientation of GFs and int...

To fabricate vapor grown carbon fibers and mesophase pitch reinforced Al matrix (VGCF/MP/Al) composites, porous VGCF/MP with high porosity was fabricated using the spacer method. Carbonization and electroless Ni plating were carried out on porous VGCF/MP to improve its thermal conductivity (TC) and wettability with Al matrix, respectively. In addit...

The improvement of thermal conductivity of tool steel is a very important problem to achieve life prolongation of a metal die used in press forming and die-casting and obtain large size or complex shape products with good mechanical properties. To improve the thermal conductivity without the degradation of mechanical properties, some kind of disper...

Al–1.5 mass%Mn was chosen as the base alloy, and 1.0 and 3.3Si were added to the base alloys, keeping the same values in the ΔMk of s-orbital energy level as those of Al–1.5Mn–0.8 and 2.4Mg alloys with superior tensile properties for as-cast applications. The Si addition or increment in the base alloy showed strengthened tensile behavior of the 0.2...

The traditional manufacturing of short fiber reinforced composites by liquid processes require preform manufacturing using inorganic binders. However, conventional preform manufacturing techniques using inorganic binder are nontrivial procedures requiring high-energy inputs for binder sintering process. A novel alternative fabrication process witho...

Ten types β-type titanium alloys for as-cast applications were proposed by using mainly ubiquitous elements in the area greatly differ from conventional alloys in compositions, in the diagram consisting of bond order (Bo) and d-orbital energy level (Md). The object was to develop β-type titanium alloys with ultimate tensile strength value of 1000 M...

To solve the problem of pore formation caused by the aggregation of carbon nanotubes (CNTs) in metal matrix composites, unidirectionally aligned CNT (CNT blocks) were used as the reinforcement material. CNT block preforms with high porosities were fabricated via a spacer method using electroless Cu-plated CNT blocks. During the preform manufacture,...

TiB2 reinforced Fe matrix composites were investigated for their potential as a new generation of hot work tools which are mainly characterized by high thermal conductivity and high hardness in comparison with conventional materials. In this work, Fe–30 vol%TiB2 composites were sintered at 1373 K for different holding times (0, 0.3, 0.6, 1.8 and 3....

Three β type titanium alloys were proposed for as-cast applications in practical fields on the basis of the d-electrons parameters with both bond order (Bot) and d-orbital energy level (Mdt). Ti–5.5Cr–5.4Mn–5.1Zr–2.8Fe with the lowest Mdt, Ti–4.5Cr–2.5Mn–1.1Al with the lowest Bot and Ti–10.8Mo–2.3Sn–1.0Al with the highest Mdt were designed by using...

TiB2 doped Fe system alloys composites as a new generation of novel materials in sustainable society show the great potential in hot work tool steels usage. Compared with SKD61, the new generation materials are focused on improving both thermal conductivity and hardness. For the suppression of TiB2 decomposition and Fe2B formation, monophase BCC st...

In this study, the coating method suitable for producing high-quality film on aluminum substrate was investigated by using different surface treatment to each specimen before electrodeposition. Microstructure of coating cross section was observed with Electron Prove Micro Analyzer (EPMA). Vickers hardness of coating surface was measured. The measur...

Short carbon fiber reinforced aluminium based matrix composites were fabricated by a low-pressure infiltration process. This study is amid for development of short carbon fiber reinforced aluminium matrix composites. Short carbon fibers of 10 vol.% was used to preparing preforms for the low-pressure infiltration process. Afterwards, pure Al and Alu...

Interfacial thermal resistance in Al-SiC composites was evaluated by comparing the measured thermal conductivity and the calculated thermal conductivity. Al-20vol.%SiC composites changing SiC particle size, 3 μm to 30 μm, was fabricated by spark plasma sintering and heat treatment. Effective thermal conductivity was measured with the steady state t...

The improvement of thermal conductivity of tool steel is extremely important for order to achieve life prolongation of metal die used in die-casting. In order to improve the thermal conductivity without the degradation of mechanical properties, VGCF (vapor grown carbon fiber) and TiB 2 particles added in tool steel (SKD61) and to obtain the composi...

Carbon fiber reinforced pure Al, A336 alloy and carbon fiber-carbon nanofiber reinforced A336 alloy composites were successfully fabricated by low-pressure infiltration process, aiming for development the carbon fiber reinforced aluminum matrix composites with high thermal conductivity and mechanical property used as functional materials and struct...

In order to obtain the high performance materials with high thermal conductivity, high electrical conductivity, low thermal expansion, good mechanical properties and low density, Graphene has higher thermal conductivity comparison with other ceramic particle. In this study, graphene dispersed aluminum (Al) composites was developed by spark plasma s...

The s-orbital energy level (Mk) of alloying elements in a Bi cluster was used to determine the composition for alloys of this system for use as Pb-free high-temperature solders. Binary Bi-Cu and Bi-Ag alloys with ΔMk of 0.013-0.343 and ternary Bi-2.0Ag-0.5Cu and Bi-5.0Ag-0.5Cu alloys with ΔMk of 0.180 and 0.379, respectively, were fabricated and te...

To investigate the degree of the effect of the interfacial thermal resistance between the matrix and the reinforcement, the effective thermal conductivity of aluminum matrix composites (Al/SiC, Al/TiB2, Al/Al2O3 and Al/SiO2) was calculated with the new simulation code which can take account of heat transfer at the interface. The critical element si...

A new process, based on an infiltration and reaction method, is proposed to fabricate metal matrix composites reinforced with Al3Ni, intermetallic compounds. This study investigates the optimum conditions for refining intermetallic compound dispersion inside the metal matrix at the different reaction times (60 s, 300 s and 600 s) at molten alloy te...

In this study, hybrid composites reinforced with Carbon short fibers and alumina short fibers were optimized using low-pressure casting. The total fraction of fibers in the composite was 10 vol%, with equal parts of Carbon short fibers and alumina short fibers (i.e., 5 vol% each). For comparison with the hybrid composites, two composites were separ...

A new process is proposed to manufacture carbon nanotube preform and carbon nanotube (vapor grown carbon fiber, VGCF)-reinforced aluminum matrix composite. Carbon nanotube preform is fabricated using a mixtures of mesophase pitch (MP) and VGCF. The VGCF-MP-preform-reinforced aluminum composite was manufactured by a low-pressure casting method, with...

Magnesium-calcium alloy composites reinforced with nickel-coated vapor-grown carbon fibers (VGCFs) were fabricated using a compo- casting process. Then, the microstructures and mechanical properties of these composites were investigated. The Mg-5Al-3Ca (AX53) alloy exhibited a dendritic microstructure with a coarse lamellar (Mg, Al)2Ca phase along...

The s-orbital energy levels (Mk) of some alloying elements in a Bi cluster model were obtained on the basis of the molecular orbital calculation. In contrast, binary Bi-Cu/-Ag/-Zn system alloys with ΔMk of 0.013-0.343 were manufactured and tension- or hardness-tested, where ΔMk was the compositional average of Mk. The ultimate tensile strength and...

0.5～1.0wt. % carbon nano-fiber (CNF) dispersed frame-resistant magnesium alloy was prepared by stir casting process. Starting materials were Mg-5wt%Al-3wt%Ca and VGCF as matrix and CNF. In order to disperse VGCF in alloy uniformly, Ni was coated on VGCF by electroless Ni plating before casting. As increasing VGCF contents, the microstructure of mat...

25 vol% Ni electroless-plated FeB powders were consolidated by spark sintering for the development of hard materials. The sintering curves of the FeB–25Ni powders were between those of as-received FeB without Ni addition and pure Ni powders. The maximum densification rate in the FeB–25Ni was achieved at an apparent relative density of 0.79, which w...

In order to obtain the high performance materials with high thermal conductivity, high electrical conductivity, low thermal expansion, good mechanical properties and low density, TiB2 particle dispersed aluminum (Al) composites was developed by spark plasma sintering. As these properties are affected by the dispersibility of the particles, the rela...

Pure aluminum (Al) has been used as high performance heat sink, electrical line and power supply line because of its light-weight, good thermal and electrical conductivities and high cost performance. On the other hand, the higher performance heat sink and eletrtorical line at room and high tempertture are reqired because of the increment of the po...

Steady state thermal conductivity measuring device was designed to measure the effective thermal conductivity of composites. Computer simulations of thermal conduction revealed that the designed device over estimates the effective thermal conductivity, and the correction coefficient was suggested. With this designed device, the effective thermal co...

FeB-Ni hard materials were consolidated by both electroless plating and spark sintering processes for the development of ubiquitous hard materials. Uniform nickel layers were formed quantitatively on as-received FeB powder surfaces. The amorphous Ni layers transformed to poly-crystalline during spark sintering. Sintering curves of FeB-Ni compacts s...

Spark sintering behaviors of 10 vol% Fe added FeB powders with 10 μm size (here after called FeB-10Fe) were investigated in spark sintering process for the development of alternative materials of WC-Co alloys. Spark sintering behaviors of FeB-10Fe in the temperature range of 600 to 1493 K were the same in the sintering curves although their maximum...

After the casting and cold drawing of fuse alloys, the joint between fuse alloys and Cu has been soldered using their parts for fabrication of AC-low voltage elements used in electric power line, which means to complex fabrication processes. As case study for the power saving, the Zn-50mass%Sn-8vol%Al2O3 and Cu was directly joined using their powde...

To investigate the degree of the effect of the interfacial thermal resistance between the matrix and the reinforcement, the effective thermal conductivity of aluminum matrix composites (Al/SiC, Al/TiB2, Al/Al2O3 and Al/SiO2) was calculated with the new simulation code which can take account of heat transfer at the interface. The critical element si...

The effectiveness of the electronic parameter on the predicting the mechanical properties of Zn system alloys for high temperature applications was evaluated in order to satisfy both the tensile strength of 200 MPa and elongation of 5%. The electronic parameter was used s-orbital energy level (ΔMk) in this study. Promising composition of alloys wer...

The goal of the present work was developing the software for calculating the electrical conductivity of aluminum-based particle-dispersed composites by using the actual microstructure images and by performing conduction simulations. However, the electrical conductivity calculated using the microstructure image was supposed to be not equivalent to t...

A new process is proposed to fabricate an aluminum alloy matrix composite dispersed with intermetallic compound particles by using the reaction between porous nickel and molten aluminum alloy. The intermetallic compound particles reinforced aluminum alloy matrix composite was manufactured with the infiltration-reaction method. Four different specif...

By optimize the mixing conditions of powders and the conditions of the spark plasma sintering, dense 20 vol % TiB2 particle aluminum composites with uniform distribution of particles were obtained. The thermal conductivity and the mechanical properties were estimated. The experimental results were good agreement with the theoretical value based on...

This study was aimed for development of vapour-grown carbon nano-fibre(VGCNF)-reinforced aluminium matrix composites by the low-pressure infiltration process. First, VGCNF and Al powder (VGCNF + Alp) preforms for low-pressure infiltration were fabricated by spark sintering process at pressures of 5, 10, 20 and 40 MPa, respectively. Porosity of the...

Unidirectional CF/Al-Si composites were fabricated by low pressure infiltration, permeating molten Al into porous CF-Si preform. In this study, the influences of Si addition in the preforms on the thermal conductivity of obtained CF/Al-Si composites were investigated in terms of the degradation of high thermal conductive CFs by chemical reactions i...

Magnesium-calcium alloy-based composites reinforced with vapor grown carbon fibers (VGCFs) are supposed to possess satisfactory high-temperature applications. However, poor wettability of magnesium with carbon fiber is a technical problem encountered in fabrication of the composites. In order to cover the wetting problem, wetting behavior of magnes...

The ultimate tensile strength of 250 MPa, 0.2% proof stress of 150 MPa, and fracture strain of 10% at the as-cast condition for Al-1.5Mn-X alloys, were objective in this development. As ternary elements, Ca, Mg, Ti and Zn were initially chosen and the values in Δ Mk of the s-orbital energy level in alloys were adjusted to be less than 0.017. Their...

The compositions of β type Ti alloys having shape-memory ability above 400K were proposed by alloying parameters used in the delectrons concept. They were both Ti-6Mo-2Al-1Sn and Ti-6Nb-3Mo which were designed for improvement of thermal stability in shape memory behavior of Ti-6Mo base alloy, preserving the tensile strength of 700 MPa. Their ingots...

Vapor grown carbon nano fiber (VGCF) dispersed Aluminum (Al) composites was prepared by two method; one is obtained by sintering after rolling of the mixed powders of aluminum particles and VGCF, and another is by rolling after sintering of the mixed powders. Relative density, fiber direction and the shape of aluminum particles in composites was es...

The tensile properties of two types of alumina (Al2O3 and Al2O3–SiO2) and short fiber-reinforced A366 alloy composite created by low-pressure infiltration have been studied. The applied pressure and temperature of molten alloy are 0.4 MPa and 1073 K, respectively. The composite containing 10 vol.% of fiber preform was sectioned and the microstructu...

The effectiveness of the electronic parameter was evaluated in order to predict the mechanical properties of zinc system alloys for high temperature application. Firstly, the relation of ultimate tensile strength or elongation and s-orbital energy level (Δ Mk) of already reported Zn system multicomponent alloys were investigated. According to this...