• Korean Journal of Materials Research
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• v.31 no.2
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• pp.61-67
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• 2021

Fabrication of a ferromagnetic composite powder for the magnesium and BaFe12O19 system by mechanical alloying (MA) is investigated at room temperature. Mixtures of Mg and BaFe12O19 powders with a weight ratio of Mg:BaFe12O19 = 4:1, 3:2, 2:3 and 1:4 are used. Optimal MA conditions to obtain a ferromagnetic composite with fine microstructure are investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that Mg-BaFe12O19 composite powders in which BaFe12O19 is dispersed in Mg matrix are successfully produced by MA of BaFe12O19 with Mg for 80 min. for all compositions. Magnetization of Mg-BaFe12O19 composite powders gradually increases with increasing the amounts of BaFe12O19, whereas coercive force of MA powders gradually decreases due to the refinement of BaFe12O19 powders with MA time for all compositions. However, it can be seen that the coercivity of Mg-BaFe12O19 MA composite powders with a weight ratio of Mg:BaFe12O19=4:1 and 3:2 for MA 80 min. are still high, with values of 1260 Oe and 1320 Oe compared to that of Mg:BaFe12O19=1:4. This clearly suggests that the refinement of BaFe12O19 powders during MA process for Mg:BaFe12O19=4:1 and 3:2 tends to be suppressed due to ductile Mg powders.

• Journal of Powder Materials
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• v.5 no.2
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• pp.89-97
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• 1998

Sintering behavior of nanostructured(NS) W-Cu powders prepared by mechanical alloying (MA) was investigated as a function of sintering temperature. MA NS W-2owt%Cu and W-3owt%Cu composite powders with the crystal size of 20-30 nm were annealed at 90$0^{\circ}C$, and thermal characteristics of those powders were investigated by DSC. Sintering behavior of MA NS W-Cu composite powders was investigated during the solid-state sintering and the Cu-liquid phase sintering. The new nanosintering phenonenon of MA W-Cu powders at solid-state sintering temperature was suggested to explain the W-grain growth in the inside of MA powders. The sintering densification of MA NS W-Cu powders was enhanced at Cu melting temperature by arrangement of MA powders, i.e., the first rearrangement of MA powders was occurred, and then the rearrangement of W-grains in the sintered parts was also took place during liquid-phase sintering, i.e., the second rearrangement was happened. Due to the double rearrangement process of MA NS W-Cu powders, the high sintered density with more than 96%o was obtained and the fine and high homogeneous state of W and Cu phases was achieved by sintering at 1200 $^{\circ}C$.

• Korean Journal of Materials Research
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• v.33 no.3
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• pp.101-105
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• 2023

A mixture of elemental Co₅₀Si₅₀ powders was subjected to mechanical alloying (MA) at room temperature to prepare a CoSi thermoelectric compound. Consolidation of the Co₅₀Si₅₀ mechanically alloyed powders was performed in a spark plasma sintering (SPS) machine using graphite dies up to 800 ℃ and 1,000 ℃ under 50 MPa. We have revealed that a nanocrystalline CoSi thermoelectric compound can be produced from a mixture of elemental Co₅₀Si₅₀ powders by mechanical alloying after 20 hours. The average grain size estimated from a Hall plot of the CoSi intermetallic compound prepared after 40 hours of MA was 65 nm. The degree of shrinkage of the consolidated samples during SPS became significant at about 450 ℃. All of the compact bodies had a high relative density of more than 94 % with a metallic glare on the surface. X-ray diffraction data showed that the SPS compact produced by sintering mechanically alloyed powders for 40-hours up to 800 ℃ consisted of only nanocrystalline CoSi with a grain size of 110 nm.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.5
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• pp.210-215
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• 2006

Mechanical alloying (MA) by high energy ball mill of pure copper and niobium powders was carried out under the Ar gas atmosphere. The supersaturated solid solution can be produced in the range up to $Cu_xNb_{100-x}$(x=5-30) by MA for 120 hrs, as demonstrated by X-ray diffraction, DSC analysis and the electronic studies through a change in the superconducting transition in the low-temperature specific heat. The $Cu_{30}Nb_{70}$ samples ball-milled for 120 hrs exhibit only a broad exothermic heat release. The total energy, ${\Delta}H_t$ accumulated during MA far the mixture of $Cu_{30}Nb_{70}$ powders increased with milling time and approached the saturation value of 7.5 kJ/mol after 120 h of milling. It can be seen that the free energy difference between the supersaturated solid solution and the mixture of $Cu_{30}Nb_{70}$ powders is estimated to be 7 kJ/mol by Miedema et al. Hence it is thermodynamically possible to assume the formation of a supersaturated solid solution phase in this system.

• Korean Journal of Materials Research
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• v.14 no.5
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• pp.310-314
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• 2004

Mechanical alloying (MA) of Ti-50.0～66.7at%Si powders was carried out in a high-energy ball mill, and in situ thermal analysis was also made during MA. In order to classify the synthesis behavior of the powders with respect to at%Si, the synthesis behavior during MA was investigated by in situ thermal analysis and X-ray diffraction (XRD). In situ thermal analysis curves and XRD patterns of Ti-50.0～59.6at%Si powders showed that there were exothermic peaks during MA, indicating TiSi, $TiS_2$, and $Ti_{5}$ $Si_4$ phase formation by a rapid exothermic reaction of self-propagating high-temperature synthesis (SHS). Those of Ti-59.8～66.7 at%Si powders, however, showed that there were no peaks during MA, indicating any Ti silicide was not synthesised until MA 240 min. For Ti-50.0～59.6at%Si powders, the critical milling times for SHS increased from 34.5 min to 89.5 min and the temperature rise, $\Delta$T (=peak temperature-onset temperature) decreased form $26.2^{\circ}C$ to $17.1^{\circ}C$ as at%Si increased. The critical composition of Si for SHS reaction was found to be 59.6at% and the critical value of the negative heat of formation of Ti-59.6at%Si to be -1.48 kJ/g.

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

• Journal of Powder Materials
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• v.28 no.5
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• pp.375-380
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• 2021

In this study, we investigate the effect of the duration of mechanical alloying on the microstructures and mechanical properties of ODS ferritic/martensitic steel. The Fe(bal.)-10Cr-1Mo pre-alloyed powder and Y₂O₃ powder are mechanically alloyed for the different mechanical alloying duration (0 to 40 h) and then constantly fabricated using a uniaxial hot pressing process. Upon increasing the mechanical alloying time, the average powder diameter and crystallite size increased dramatically. In the initial stages within 5 h of mechanical alloying, inhomogeneous grain morphology is observed along with coarsened carbide and oxide distributions; thus, precipitate phases are temporarily observed between the two powders because of insufficient collision energy to get fragmented. After 40 h of the MA process, however, fine martensitic grains and uniformly distributed oxide particles are observed. This led to a favorable tensile strength and elongation at room temperature and 650℃.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.112-122
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• 1995

Metal hydride alloys of TiFe based system have been produced by mechanical alloying(MA) method and their electrochemical characteristics have been evaluated for application for Ni/MH battery electrode. These alloys became amorphous after 36hrs ball milling and easily activated electrochemically. All MA amorphous alloys reached at the first charge/discharge cycle the maximum capacity which was 2-3 times higher than the crystalline state. But their cyclic lives were much inferior to the crystalline state. Alloying elements such as Ni, Co, Cr, Mo substituting Fe greatly improved the capacity and 180 mAh/g capacity was obtained in an alloy of TiFe_{0.6}Ni_{0.1}Co_{0.1}Cr_{0.1}Mo_{0.1}$.

• Journal of Powder Materials
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• v.3 no.1
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• pp.42-48
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• 1996

To investigate the phase transformation behaviors of mechanically alloyed Nb-25 at%Al powders, the mixed Nb-25 at%Al powders were mechanically alloyed in SPEX 8000 Mixer/Mill. Mechanical alloying(MA) time was varied between 0.5 hour and 72 hours. The phase formation behaviors of these mechanically alloyed powders were examined using X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), and differential thermal analysis(DTA). Appreciable amorphization started from 6 hours of MA. The powders mechanically alloyed for 10 hours were in almost amorphous phase. DTA results showed that the powders mechanically alloyed for 12 hours had a strong exothermic peak about$600^{\circ}C$, whereas the powders mechanically alloyed for 6 hours had two exothermic peaks. The first peak was found to be due to the stress relief effect and the second one due to the formation of$Nb_{3}Al,Nb_{2}Al and Nb_{2}C$phases by crystallization.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.4
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• pp.129-134
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• 2004

In this study, we investigated the effect of a nitrogen atom on the amorphization of V-Fe alloy through solid-gas reaction during mechanical alloying (MA). MA by planetary ball mill of $V_{70}Fe_{30}$ elemental powders was carried out under the nitrogen gas atmosphere. Amorphization has been observed after 160 hours of ball milling in this case. The DSC spectrum for the mechanically alloyed ($V_{70}Fe$_{30}$)_{0.89}N_{0.11}$ powders exhibits a sharp exothermic peak due to crystallization at about $600^{\circ}C$. Structural transformation from the bcc crystalline to amorphous states was also observed through X-ray and neutron diffractions. We take a full advantage of a negligibly small scattering length of the V atom in the neutron diffraction measurement. During amorphization process the octahedral unit, which is typical of a polyhedron formed in any crystal structures, was preferentially destroyed and transformed into the tetrahedral unit. Futhermore, neutron diffraction measurements revealed that a nitrogen atom is selectively situated at a center of the polyhedron formed by V atoms.