• Journal of Powder Materials
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• v.14 no.6
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• pp.354-361
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• 2007

The bi-materials with Al-Mg alloy and its composites reinforced with SiC and $Al_2O_3$ particles were prepared by conventional powder metallurgy method. The A1-5 wt%Mg and composite mixtures were compacted under $150{\sim}450\;MPa$, and then the mixtures compacted under 400 MPa were sintered at $773{\sim}1173K$ for 5h. The obtained bi-materials with Al-Mg/SiCp composite showed the higher relative density than those with $Al-Mg/Al_2O_3$ composite after compaction and sintering. Based on the results, the bi-materials compacted under 400 MPa and sintered at 873K for 5h were used for mechanical tests. In the composite side of bi-materials, the SiC particles were densely distributed compared to the $Al_2O_3$ particles. The bi-materials with Al-Mg/SiC composite showed the higher micro-hardness than those with $Al-Mg/Al_2O_3$ composite. The mechanical properties were evaluated by the compressive test. The bi-materials revealed almost the same value of 0.2% proof stress with Al-Mg alloy. Their compressive strength was lower than that of Al-Mg alloy. Moreover, impact absorbed energy of bi-materials was smaller than that of composite. However, the bi-materials with Al-Mg/SiCp composite particularly showed almost similar impact absorbed energy to $Al-Mg/Al_2O_3$ composite. From the observation of microstructure, it was deduced that the bi-materials was preferentially fractured through micro-interface between matrix and composite in the vicinity of macro-interface.

• Korean Journal of Materials Research
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• v.14 no.5
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• pp.305-309
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• 2004

Mechanical alloying (MA) of Ti-25.0～37.5at%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-25.0～26.1at%Si powders showed that there were no peaks during MA, indicating $Ti_{5}$ $Si_3$ was synthesised by a slow reaction of solid state diffusion. Those of Ti-27.1～37.5at%Si powders, however, showed that there were exothermic peaks during MA, indicating $_Ti{5}$ $Si_3$ and$ Ti_3$Si phase formation by a rapid exothermic reaction of self-propagating high-temperature synthesis (SHS). For Ti-27.1～37.5at%Si powders, the critical milling times for SHS decreased from 38.1 to 18.5 min and the temperature rise, ΔT (= peak temperature - onset temperature) increased form $19.5^{\circ}C$ to $26.7^{\circ}C$ as at%Si increased. The critical composition of Si for SHS reaction was found to be 27.1at% and the critical value of the negative heat of formation of Ti-27.1at%Si to be -1.32 kJ/g.

• 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.

• Korean Journal of Dental Materials
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• v.44 no.1
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• pp.69-77
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• 2017

The aim of this study was to investigate the effects of chitosan powder addition on the strengthening of conventional glass ionomer cement. Two types of chitosan powders with different molecular weight were mixed with conventional glass ionomer cement (GIC): low-molecular weight chitosan (CL; 50~190 kDa), high-molecular weight chitosan (CH; 310~375 kDa). The chitosan powders (CL and CH) were separately added into the GIC liquid (0.25-0.5 wt%) under magnetic stirring, or mixed with the GIC powder by ball-milling for 24 h using zirconia balls. The mixing ratio of prepared cement was 2:1 for powder to liquid. Net setting time of cements was measured by ISO 9917-1. The specimens for the compressive strength (CS; $4{\times}6mm$), diametral tensile strength (DTS; $6{\times}4mm$), three-point flexure (FS; $2{\times}2{\times}25mm$) with flexure modulus (FM) were obtained from cements at 1, 7, and 14 days after storing in distilled water at $(37{\pm}1)^{\circ}C$. All mechanical strength tests were conducted with a cross-head speed of 1 mm/min. Data were statistically analyzed by one-way ANOVA and Tukey HSD post-hoc test. The mechanical properties of conventional glass ionomer cement was significantly enhanced by addition of 0.5 wt% CL to cement liquid (CS, DTS), or by addition of 10 wt% CH (FS) to cement powder. The CL particles incorporated into the set cement were firmly bonded to the GIC matrix (SEM). Within the limitation of this study, the results indicated that chitosan powders can be successfully added to enhance the mechanical properties of conventional GIC.

• Korean Journal of Metals and Materials
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• v.50 no.11
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• pp.817-822
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• 2012

Nano powders of $Al_2O_3$ and $TiO_2$ compounds made by high energy ball milling were pulsed current activated sintered for studying their sintering behaviors and mechanical properties. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Nano-structured $Al_2TiO_5$ with small amount of $Al_2O_3$ and$TiO_2$ was formed by sintering at $1300^{\circ}C$ for 5 minute, in which average grain size was about 96 nm. Hardness and fracture toughness of the nano-structured $Al_2TiO_5$ compound with a small amount of $Al_2O_3$ and$TiO_2$ were $602kg/mm^2$ and $2.6MPa{\cdot}m^{1/2}$, respectively.

• Korean Journal of Metals and Materials
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• v.50 no.12
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• pp.891-896
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• 2012

Nanopowders of MgO and $TiO_2$ were made by high energy ball milling. The rapid synthesis and sintering of the nanostructured $MgTiO_3$ compound was investigated by the high-frequency induction heated sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition grain growth. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid for the application of nanomaterials. A highly dense nanostructured $MgTiO_3$ compound was produced with simultaneous application of 80 MPa pressure and induced current within 2 min. The sintering behavior, gain size and mechanical properties of $MgTiO_3$ compound were investigated.

• Korean Journal of Metals and Materials
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• v.49 no.5
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• pp.374-379
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• 2011

Nano-powders of $Ti_3Al$ and $2Al_2O_3$ were synthesized from $3TiO_2$ and 5Al powders by high energy ball milling. A nanocrystalline $Al_2O_3$ reinforced composite was consolidated by pulsed current activated sintering within 2 minutes from mechanochemically synthesized powders of $Al_2O_3$ and $Ti_3Al$. Nanocrystalline materials, have received much attention as advanced engineering materials due to their improved physical and mechanical properties. The relative density of the composite was 99.5%. The average obtained hardness and fracture toughness values were 1510 kg/$mm^2$ and $9\;MPa{\cdot}m^{1/2}$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.245-251
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• 2015

We have applied mechanical alloying (MA) to produce soft magnetic composite material using a mixture of elemental $Fe_2O_3$-Mg powders. An optimal milling and heat treatment conditions to obtain soft magnetic ${\alpha}$-Fe/MgO composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that ${\alpha}$-Fe/MgO composite powders in which MgO is dispersed in ${\alpha}$-Fe matrix are obtained by MA of $Fe_2O_3$ with Mg for 30 min. The saturation magnetization of ball-milled powders increases with increasing milling time and reaches to a maximum value of 69.5 emu/g after 5 h MA. The magnetic hardening due to the reduction of the ${\alpha}$-Fe grain size by MA was also observed. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at $800{\sim}1000^{\circ}C$ under 60 MPa. X-ray diffraction result shows that the average grain size of ${\alpha}$-Fe in ${\alpha}$-Fe/MgO nanocomposite sintered at $800^{\circ}C$ is in the range of 110 nm.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.3
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• pp.121-127
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• 2007

We have applied mechanical alloying (MA) to get $Mg_2Si$ thermoelectric material with nano-sized grains. An optimal milling and heat treatment conditions to obtain the single phase of $Mg_2Si$ compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry (DSC) measurement. The $Mg_{66.7}Si_{33.3}$ MA samples ball-milled for $20{\sim}180\;hrs$ exhibit two broad exothermic heat releases around $220^{\circ}C$ and $570^{\circ}C$. On the other hand, MA sample ball-milled far 260 hrs exhibits only a sharp exothermic peak at $230^{\circ}C$ Single phase Mg2Si powder can be obtained by MA of $Mg_{66.7}Si_{33.3}$ mixture for 60 hours and subsequently heated up to $620^{\circ}C$. Sintering of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $800{\sim}900^{\circ}C$ under 50 MPa. The shrinkage of sintering sample during SPS was significant at about $200^{\circ}C$. All compact bodies have a high relative density above 94% with metallic glare on the surface.

• Korean Journal of Materials Research
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• v.24 no.9
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• pp.495-501
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• 2014

Despite having many attractive properties, $ZrO_2$ ceramic has a low fracture toughness which limits its wide application. One of the most obvious tactics to improve its mechanical properties has been to add a reinforcing agent to formulate a nanostructured composite material. Nanopowders of $ZrO_2$ and Cr were synthesized from $CrO_3$ and Zr powder by high energy ball milling for 10 h. Dense nanocrystalline $2/3Cr-ZrO_2$ composite was consolidated by a high-frequency induction heated sintering method within 5 min at $600^{\circ}C$ from mechanically synthesized powder. The method was found to enable not only rapid densification but also the inhibition of grain growth, preserving the nano-scale microstructure. Highly dense $2/3Cr-ZrO_2$ composite with relative density of up to 99.5% was produced under simultaneous application of a 1 GPa pressure and the induced current. The hardness and fracture toughness of the composite were 534 kg/mm2 and $7MPa{\cdot}m1/2$, respectively. The composite was determined to have good biocompatibility.