• Journal of Powder Materials
• /
• v.17 no.2
• /
• pp.113-122
• /
• 2010

Two kinds of oxide-dispersion-strengthened (ODS) 316L stainless steel were manufactured using a wet mixing process(wet) and a mechanical alloying method (MA). An MA 316L ODS was prepared by a mixing of metal powder and a mechanical alloying process. A wet 316L ODS was manufactured by a wet mixing with 316L stainless steel powder. A solution of yttrium nitrate was dried after being in the wet 316L ODS alloy. The results showed that carbon and oxygen were effectively reduced during the degassing process before the hydroisostatic process (HIP) in both alloys. It appeared that the effect of HIP treatment on increase in impact energy was pronounced in the MA 316L ODS alloy. The MA 316L ODS alloy showed a higher yield strength and a smaller elongation, when compared to the wet 316L ODS alloy. This seemed to be attributed to the enhancement of bonding between oxide and matrix particles from HIP and to the presence of a finer oxide of about 20 nm from the MA process in the MA 316L ODS alloy.

• Proceedings of the KIEE Conference
• /
• 1994.07b
• /
• pp.1333-1335
• /
• 1994

The nitrification of pure iron powders is found to occur even at room temperature by high energy ball milling in $NH_3$ gas atmosphere. The powders of metastable iron nitrides ($0<at.%N{\le}23.3$) thus produced are identified as the super-saturated bee structure for the N content below 14.9 at.%N and the high temperature phase of the hcp structure above 19.4 at.%N. The atomic volume of Fe in the bcc phase is found to be smaller than that of the N-martensite reported in the literature. Magnetization at room temperature gradually decreases with increasing the N concentration in contrast to the enhancement reported for the bet nitrides. Neutron diffraction experiment also provide detailed information about the local structure surrounding the nitrogen atom. The coordination number of Fe atom around a nitrogen atom for the iron nitride containing 9.5 at.%N turns out to be 3.9 atoms.

• Journal of Powder Materials
• /
• v.17 no.3
• /
• pp.235-241
• /
• 2010

Mo nanopowder was synthesized by ball-milling and subsequent hydrogen-reduction of $MoO_3$ powder. To fabricate ultra fine grained molybdenum, two-step sintering and spark plasma sintering process were employed. The grain size of specimen by two-step sintering and spark plasma sintering was around $0.6\;{\mu}m$ and $0.4\;{\mu}m$, respectively. Mechanical properties of ultra fine grained Mo with relative density of above 90% were significantly improved at room and high temperatures comparing to commercial bulk Mo of 99% relative density. This result was mainly explained by the grain size refinement due to diffusion-controlled sintering.

• Korean Journal of Metals and Materials
• /
• v.50 no.12
• /
• pp.961-966
• /
• 2012

Nano-sized Co and $Al_2O_3$ powders were successfully synthesized from $3/4Co_3O_4$ and 2Al by high-energy ball milling. A dense nanocrystalline $2.25Co-Al_2O_3$ composite was consolidated from mechanically synthesized powders by the pulsed current activated sintering (PCAS) method within 2 min. Consolidation was accomplished under the combined effects of a pulsed current and mechanical pressure. A dense $2.25Co-Al_2O_3$ with relative density of up to 95% was produced under simultaneous application of a 80 MPa pressure and a pulsed current of 2800 A. The fracture toughness and hardness of the $2.25Co-Al_2O_3$ composite were $8MPa{\cdot}m^{1/2}$, $870kg/mm^2$, respectively.

• Korean Journal of Metals and Materials
• /
• v.50 no.6
• /
• pp.449-454
• /
• 2012

Nanopowder of FeAl and $Al_2O_3$ was synthesized from FeO and Al powders by high energy ball milling. Using the pulsed current activated sintering method, the nanocystalline $Al_2O_3$ reinforced FeAl composite was consolidated within two minutes from mechanically synthesized powders. The advantage of this process is that it allows very quick densification to near theoretical density and prohibits grain growth in nanostuctured materials. The grain size, sintering behavior and hardness of sintered $FeAl-Al_2O_3$ composite were investigated.

• Korean Journal of Materials Research
• /
• v.21 no.7
• /
• pp.384-390
• /
• 2011

Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. $Ti_2O$, CaO, $CaTiO_3$, and $Ti_xP_y$ phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.

• Journal of Powder Materials
• /
• v.9 no.6
• /
• pp.394-408
• /
• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• Advances in nano research
• /
• v.13 no.4
• /
• pp.313-323
• /
• 2022

The microstructure and mechanical properties of Cr-Ni steel and Cr-Ni steel-matrix nanocomposites reinforced with nano-ZrO₂ particles were investigated in this study. Cr-Ni steel and Cr-Ni/ZrO₂ nanocomposites were produced using a combination of high-energy ball milling, pressing, and sintering processes. The microstructures of the specimens were analyzed using EDX and XRD. Compression and hardness tests were performed to determine the mechanical properties of the specimens. Nano-ZrO₂ particles were effective in preventing chrome carbide precipitate at the grain boundaries. While t-ZrO₂ was detected in Cr-Ni/ZrO₂ nanocomposites, m-ZrO₂ could not be found. Few α'-martensite and deformation bands were formed in the microstructures of Cr-Ni/ZrO₂ nanocomposites. Although nano-ZrO₂ particles had a negligible impact on the strength improvement provided by deformation-induced plasticity mechanisms in Cr-Ni/ZrO₂ nanocomposites, the mechanical properties of Cr-Ni steel were significantly improved by using nano-ZrO₂ particles. The hardness and compressive strength of Cr-Ni/ZrO₂ nanocomposite were higher than those of Cr-Ni steel and enhanced as the weight fraction of nano-ZrO₂ particles increased. Cr-Ni/ZrO₂ nanocomposite with 5wt.% nano-ZrO₂ particles had almost twofold the hardness and compressive strength of Cr-Ni steel. The nano-ZrO₂ particles were considerably more effective on particle-strengthening mechanisms than deformation-induced strengthening mechanisms in Cr-Ni/ZrO₂ nanocomposites.

• Journal of Powder Materials
• /
• v.9 no.6
• /
• pp.381-393
• /
• 2002

Recent developments in nanocrystalline and nanocomposite rare earth-transition metal magnets are reviewed and emphasis is placed on research work at IFW Dresden. Principal synthesis methods include high energy ball milling, melt spinning, mold casting and hydrogen assisted methods such as reactive milling and hydrogenation-disproportionation-desorption-recombination. These techniques are applied to NdFeB-, PrFeB- and SmCo-type systems with the aim to produce high remanence magnets with high coercivity. Concepts of maximizing the energy density in nanostructured magnets by either inducing a texture via anisotropic HDDR or hot deformation or enhancing the remanence via magnetic exchange coupling are evaluated. With respect to high temperature applications melt spun $Sm(Co_{0.74}Fe_{0.1}Cu_{0.12}Zr_{0.04})_{7.5}$ ribbons were prepared, which showed coercivities of up to 0.53 T at 50$0^{\circ}C$. Partially amorphous $Nd_{60}Fe_xCo_{30-x}Al_{10}(0{\leq}x{\leq}30)$ alloys were prepared by copper mold casting. The effect of transition metal content on the glass-forming ability and the magnetic properties was investigated. The $Nd_{60}Co_{30}Al_{10}$ alloy exhibits an amorphous structure shown by the corresponding diffraction pattern. A small substitution of Co by 2.5 at.% Fe results In the formation of Fe-rich crystallites embedded in the Nd-rich amorphous matrix. The Fe-rich crystallites show hard magnetic behaviour at room temperature with a coercivity value of about 0.4 T, relatively low saturation magnetization and a Curie temperature of 500 K.

• Korean Journal of Metals and Materials
• /
• v.49 no.7
• /
• pp.565-569
• /
• 2011

Nanopowders of MgO, $Al_2O_3$ and $SiO_2$ were made by high-energy ball milling. The fast sintering of nanostructured $Al_2O_3-MgSiO_3-SiO_2$ composites was investigated from mechanically activated powders of MgO, $Al_2O_3$ and $SiO_2$ by a pulsed-current activated sintering process. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties; in particular greater strength, hardness, excellent ductility and toughness. Highly dense nanostructured $Al_2O_3- MgSiO_3-SiO_2$ composites were produced with simultaneous application of 80 MPa and pulsed output current of 2800A within 2 minutes. The sintering behavior, grain size and mechanical properties of $Al_2O_3-MgSiO_3-SiO_2$ composites were investigated.