Hansang Kwon

Dual-nanoparticulate-reinforced aluminum matrix composite materials

Aluminum (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nano-SiC) were fabricated by mechanical ball milling, followed by hot-pressing. Nano-SiC was used as an active mixing agent for dispersing the CNTs in the Al powder. The hardness of the produced composites was dramatically increased, up to eight times higher than bulk pure Al, by increasing the amount of nano-SiC particles. A small quantity of aluminum carbide (Al(4)C(3)) was observed by TEM analysis and quantified using x-ray diffraction. The composite with the highest hardness values contained some nanosized Al(4)C(3). Along with the CNT and the nano-SiC, Al(4)C(3) also seemed to play a role in the enhanced hardness of the composites. The high energy milling process seems to lead to a homogeneous dispersion of the high aspect ratio CNTs, and of the nearly spherical nano-SiC particles in the Al matrix. This powder metallurgical approach could also be applied to other nanoreinforced composites, such as ceramics or complex matrix materials.

Effective load transfer by a chromium carbide nanostructure in a multi-walled carbon nanotube/copper matrix composite.

Multi-walled carbon nanotube (MWCNT) reinforced copper (Cu) matrix composites, which exhibit chromium (Cr) carbide nanostructures at the MWCNT/Cu interface, were prepared through a carbide formation using CuCr alloy powder. The fully densified and oriented MWCNTs dispersed throughout the composites were prepared using spark plasma sintering (SPS) followed by hot extrusion. The tensile strengths of the MWCNT/CuCr composites increased with increasing MWCNTs content, while the tensile strength of MWCNT/Cu composite decreased from that of monolithic Cu. The enhanced tensile strength of the MWCNT/CuCr composites is a result of possible load-transfer mechanisms of the interfacial Cr carbide nanostructures. The multi-wall failure of MWCNTs observed in the fracture surface of the MWCNT/CuCr composites indicates an improvement in the load-bearing capacity of the MWCNTs. This result shows that the Cr carbide nanostructures effectively transferred the tensile load to the MWCNTs during fracture through carbide nanostructure formation in the MWCNT/Cu composite.

Effect of magnetic field on the electrodeposition of Fe, Co into the pores of anodic film on aluminum

Ferromagnetic Fe or Co was electrodeposited into the pores in aluminum anodic oxide film to produce a magnetic anodic film, and the effects of magnetic field during electrodeposition on the deposition characteristics of the metals and coercivity of the produced anodic film were investigated. Fe was electrodeposited into the pores in anodic film using a mixed solution (pH=3.8) of FeSO4(NH4)SO4.6H2O (0.20 mol/l) and H3BO4 (0.48 mol/l) at 20 °C with constant applied voltage of 10 V, and Co using a mixed solution (pH=4.5) of CoSO4,7H2O (0.10 mol/l) and H3BO4 (0.48 mol/l). It has been found that for the Fe-deposited anodic film the coercivity increased with increasing length of deposited Fe particles and decreased with increasing diameter (or porosity). The application of magnetic field during electrodeposition of Fe had little influence on the coercivity of the anodic film. For the Co-deposited anodic film the coercivity increased with increasing length of deposited Fe particles and increased unexpectedly wit...

Fabrication of Carbon Nanotube Reinforced Aluminum Composite by Powder Extrusion Process

This paper describes a fabrication process of Al/CNT composites and investigated their mechanical properties. CNT is a very useful reinforcement for composites since it has a very high strength and very high Young’s modulus. However, it is very difficult to distribute CNT in a metal matrix. Natural rubber was used as an elastomer and mixed with Al powder and CNT precursors to improve the distribution of the CNT in Al matrix. The resulting powder mixture was filled into Al alloy billets and encapsulated in vacuum atmosphere. The billets were then extruded with different extrusion ratios of 5, 10 and 20 at 673K. The composites were observed under optical microscope and FE-SEM, and the mechanical properties were evaluated by Vickers hardness and tensile tests. We succeeded in obtaining fully densified and finely extruded rod of Al/CNT composites of well distributed CNT by hot extrusion process. Observation of post extrusion micro structures revealed that CNT were not damaged by the hot extrusion process and their Vickers hardness and tensile strengths obtained were about twice compared to pure Al.

Study on the effect of repeated HDDR on the coercivity of Sm2Fe17Nx material

Abstract Sm 2 Fe 17 -type alloy with chemical composition of Sm 22.7 wt%, Fe 72.3 wt% and Nb 5.0 wt% was repeatedly HDDR-treated before nitrogenation in order to produce a Sm 2 Fe 17 N x material with fine and homogeneous grain structure, thus enhancing its coercivity. The hydrogenation and disproportionation characteristics of the HDDR-treated alloy were examined. The grain refinement of nitride due to the repeated HDDR treatment was also examined using a Hopkinson effect in TMA. It was found that the hydrogenation temperature of the alloy was not significantly influenced by the previous HDDR treatment, while the disproportionation temperature was significantly lowered by it. The nitride prepared from double HDDR-treated alloy exhibited a remarkably higher coercivity, and this enhancement was explained by a finer and more homogeneous grain structure due to double HDDR treatment.

Decomposition of DyF3 and its effect on magnetic performance of DyF3-doped Nd-Fe-B-type hot-deformed magnet

Decomposition of DyF3 and its effect on the magnetic performance of the hot-pressed compact and die-upset magnet of melt-spun Nd-Fe-B-type material were investigated. DyF3 was thermally decomposed above 660 °C, and this decomposition was linked closely to the coercivity enhancement. When the DyF3 doped flakes were hot-pressed above the decomposition temperature of DyF3, the diffusion of Dy into the flakes was promoted, and leading to profound coercivity enhancement. Coercivity of the hot-pressed magnet was further enhanced by post-hot-press annealing, and coercivity as high as 24.5 kOe was obtained after the optimum annealing. The DyF3 doped hot-deformed magnet exhibited enhanced magnetic performance (iHc = 17.5 kOe, Br = 12.8 kG, (BH)max = 37.6 MGOe) with respect to the un-doped magnet without sacrificing significant remanence. Coercivity was improved by 30%. In magnet in which the decomposition of DyF3 and Dy diffusion were fully accomplished, the region originally occupied by added DyF3 was completely ...

Fabrication of a Functionally Graded Copper-Zinc Sulfide Phosphor

Functionally graded materials (FGMs) are compositionally gradient materials. They can achieve the controlled distribution of the desired characteristics within the same bulk material. We describe a functionally graded (FG) metal-phosphor adapting the concept of the FGM; copper (Cu) is selected as a metal and Cu- and Cl-doped ZnS (ZnS:Cu,Cl) is selected as a phosphor and FG [Cu]-[ZnS:Cu,Cl] is fabricated by a very simple powder process. The FG [Cu]-[ZnS:Cu,Cl] reveals a dual-structured functional material composed of dense Cu and porous ZnS:Cu,Cl, which is completely combined through six graded mediating layers. The photoluminescence (PL) of FG [Cu]-[ZnS:Cu,Cl] is insensitive to temperature change. FG [Cu]-[ZnS:Cu,Cl] also exhibits diode characteristics and photo reactivity for 365 nm -UV light. Our FG metal-phosphor concept can pave the way to simplified manufacturing of low-cost and can be applied to various electronic devices.

Functionally Graded Dual-Nanoparticulate-Reinforced Aluminum Matrix Composite Materials

Functionally graded carbon nanotubes (CNT) and nano Silicon carbide (nSiC) reinforced aluminum (Al) matrix composite materials were fully densified by a simple ball milling and hot-pressing processes. The nSiC was used as a physical mixing agent to increase dispersity of the CNT in the Al particles. It was observed that the CNT was better dispersed in the Al particles with a nSiC mixing agent compared to without it used. SEM micrograph showed that the interface of the each layers had very tightly adhesion without any serious pores and micro-cracks. This functionally graded dual-nanoparticulate-reinforced Al matrix composite by powder metallurgical approach could also be applied to comples matrix materials.

Effect of Spark Plasma Sintering in Fabricating Carbon Nanotube Reinforced Aluminum Matrix Composite Materials

Carbon nanotubes (CNT) are attractive next generation materials due to their unique properties, which lead to high mechanical, electrical, and thermal performance (Iijima, 1991; Endo et al., 1976; Niyogi et al., 2002; Komarov & Mirnov, 2004). This unique nano order material can not only be utilized on its own in precision industrial fields but can also provide high performance functionality in conjunction with conventional materials. For this reason, many researchers are investigating the fabrication of CNT reinforced metal, ceramic, and polymer matrix composite materials. Despite their research efforts, the fabrication of CNT-reinforced metal matrix composite materials, particularly with an aluminum (Al) matrix, is still facing several problems, such as difficulties in homogeneously dispersing the CNT in the Al matrix, (Salvetat-Delmotte and Rubio, 2002; Hilding et al., 2003; Xu et al., 1999) producing highly densified composite materials without any degradation of the CNT, (Kuzumaki et al., 1998; Sridhar & Narayana, 2009) and achieving enough interface strength between the Al matrix and reinforcement of CNT (Deng et al., 2007; Bakshi et al., 2009; Lahiri et al., 2009). To overcome these problems, Deng et al. fabricated the CNT-Al alloy composite materials by cold isostatic pressing and then subsequent hot extrusion techniques, with which they have achieved 45% incremental increase in tensile strength (Deng et al., 2007) Esawi et al. attempted to fabricate a CNT-Al matrix composite by mechanical milling and rolling or extrusion processes (Esawi & Morsi, 2007; Esawi & Borady, 2008; Esawi et al., 2009). Morsi et al. produced CNT-Al matrix composites by a unique powder metallurgy route using spark plasma extrusion (Morsi et al., 2009; 2010). Agawal et al. introduced several fabrication methods for CNT-Al and Al alloy composites based on thermal and cold spray forming technologies (Laha et al., 2004; Bakshi et al., 2008; Bakshi & Agarwal, 2010). Recently, we have also demonstrated the feasibility of making aluminum-carbon nanotube (Al-CNT) composite materials, producing not only a highly densified composite but also enhanced interface bonding between the Al matrix and CNT, by a combination of spark plasma sintering (SPS) followed by hot extrusion processes (Kwon et al., 2009; Kwon & Kawasaki, 2009; Kwon et al., 2010). However, the specific effect

Mechanical behaviour of dual nanoparticle-reinforced aluminium alloy matrix composite materials depending on milling time:

Aluminium 6061 alloy matrix composite materials reinforced with carbon nanotubes (CNTs) and silicon carbide nanoparticles (nSiCs) were prepared by high-energy ball milling and hot pressing. In addition to inducing fine particle strengthening, nSiCs were also used as a solid mixing agent to improve the dispersion of the CNTs in the Al matrix powder. The dependence of the densification and mechanical strength of the composites reinforced with the dual nanoparticles on the milling time is discussed. The crystallite sizes of Al in the composites were also investigated. Moreover, the relative defect ratios of the CNTs in the composites were calculated from the intensities of the D and G peaks of the Raman spectra. With this new approach to composite fabrication, a hardness and tensile strength of 334 HV and 293 MPa, respectively, were achieved. The high-energy ball milling time significantly affected the microstructure and mechanical properties of the composites; however, the dual nanoparticle reinforcement can potentially be used in a variety of industrial component materials with precisely controlled material properties.