Solid State Phenomena Vol. 118

Abstract: The effect of MPC pressure on the density, microstructure, mechanical properties, and electrical property of MPCed and sintered bulk was investigated. A detail characterization of the MPCed and sintered bulk has been performed using XRD, SEM, TEM, Vickers hardness tester, and breakdown voltage tester. The alumina powder used in this research has a size of 50-200 nm, a smooth surface and elliptical shape. The obtained density of MPCed and sintered bulk is increased with increasing MPC pressure from 0.5 to 1.25 GPa. The highest density of 92% in this research is obtained in the MPCed at 1.25 GPa and sintered bulk, while it is 90 % in the MPCed at 0.5 GPa. The different Vickers hardness with MPC pressure is associated with the different density and grain size of bulks. The maximum breakdown voltage of 47 kV/cm is achieved in the bulk MPCed at 1.25 GPa due to the higher density than that of others. In addition, the fracture mechanism of MPCed and sintered bulk is discussed.

Abstract: Phase selection and microstructural morphology change of the Cu47Ti33Zr11Ni6Sn2Si1 alloy were investigated through the droplet emulsion technique(DET). The emulsified Cu47Ti33Zr11Ni6Sn2Sil alloy powders showed several different microstructures depending on the amount of undercooling. The amount of undercooling of the powders was monitored by differential thermal analysis and was matched with the microstructures. The phase transition of Cu47Ti33Zr11Ni6Sn2Sil alloy powders according to the increase of undercooling proceeds by the process Cu4Ti3 +CuTi +Cu2Ti +Cu51Zr14 → Cu4Ti3 + CuTi + Cu2Ti + Cu51Zr14 + CuTi2 → Cu2Ti + Cu51Zr14 + CuTi2 → Cu51Zr14 +CuTi2. Specifically, the morphology and scale of the CuTi2 phase were examined by SEM observation, and area fraction measurement using an image analyzer, transmission electron microscopy studies, and microhardness tests showed that the amorphous phase could be synthesized by DET. A microstructure selection map of Cu47Ti33Zr11Ni6Sn2Sil alloy powders for tailored solidification was also suggested.

Abstract: Cu oxide nano powders were synthesized by the levitational gas condensation (LGC) method, and heated at temperature ranges from 150 to 450
C. The nano powders consist of mainly Cu2O with an average size of 35 nm. The analysis of the IR-spectra of the nanopowders demonstrates that the surface of the sample under an air exposure is coated by hydroxylhydride (-OH, H2O) and hydroxycarbonated [Cu2(OH)2CO3]. The change of the particle size by heat treatment below 450 °C is relatively small. The variation of the adsorption ability is mainly defined under heating at least up to 300 °C, by the surface state of the particles. The catalytic effect was increased at heat treated samples.

Abstract: Hydroxyapatite (Ca10(PO4)6(OH)2, HAp) powders is synthesized using the mixed powders of CaCO3 refined from oyster shells and phosphoric acid (H3PO4-98%, Daejung) as starting materials. The characteristic evaluation and chemical analysis of the synthesized powders is performed by X-ray diffraction (XRD), Fourier-transformed infra-red spectroscopy (FT-IR), and inductively-coupled plasma atomic emission spectroscopy (ICPAES). XRD analysis of synthetic powder by heat treatment at 1300°C for 2hrs shows only HAp peaks corresponding to stoichiometric HAp. It is confirmed by ICP-AES test that impurities such as Zn, In, Ti, Ba, Cd, Pb, and Mn, is not detected at all, but small amounts of Ti and Be is observed (0.099ppm Ti and 0.002ppm Ba). Variation of bone density is measured by giving medication of HAp powder with drinking water into human body continuously for three month. After the medication, the bone density is higher than the medication before. This means that HAp powder made from this process can be used as improver of bone density.

Abstract: Nanostructure formation of fully amorphous Al86Ni9Mm5 alloys in both as solidified amorphous and annealed nanocomposite conditions was investigated using XRD, DSC, and TEM. The exothermic reaction peak of DSC is associated with the crystallization of fcc-Al, Al3Ni, and A111Ce3 phase. The microstructure of annealed specimen at 250 oC consists of a random distribution of fine nanocrystalline fcc-Al crystals embedded in the amorphous matrix. During primary crystallization, partitioning of the solute atoms takes place at the interface, resulting in an increase of solute atoms in the amorphous and interdendritic resign. The final microstructure shows a homogeneous distribution of intermetallic compounds embedded in the Al matrix. The hardening effect of nanostructured specimens annealed at 250 oC is attributed to both solute enrichment in the amorphous matrix and formation of fcc-Al crystallites. The highest hardness of 490 Hv in this research is obtained in the specimen heat treated at 300 oC for 20 min.

Abstract: The particle size effect on the peritectic melting of FeSn2 particles in FeSn-FeSn2 nanocomposites was studied using differential scanning calorimetry and X-ray diffraction. FeSn-10 wt.% FeSn2 compounds, mechanically milled for 30 min and slowly heated in a differential scanning calorimeter, showed incongruent melting at 680 K. Although FeSn2 grains grew from 10 to 40 nm upon heating before peritectic melting set in, the melting temperature was more than 100 K lower than the equilibrium value. A small latent heat during peritectic melting and a large amount of interfacial energy of FeSn-FeSn2 nanocomposites are held responsible for this large particle size effect. Grain growth is hardly possible in the case of rapid local heating during mechanical milling. Therefore, a decrease in the peritectic melting temperature is even expected to be substantially larger.

Abstract: This work reports on the production of Cu-Hf-Ti bulk glassy composites through a powder metallurgical route, i.e. by mechanical alloying and subsequent spark-plasma sintering. Powders of Cu60Hf30Cu10 and Cu60Hf25Ti15 composition were prepared using a high-energy planetary ball-mill. Both alloys nearly showed a fully amorphous structure with only a small fraction of residual HCP Hf grains left after 50 h of milling. Differential scanning calorimetry (DSC) analyses of the milled glassy powder revealed a two-stage crystallization process for both compositions. However, the released crystallization enthalpy was substantially larger for the Cu60Hf25Ti15 alloy than for the Cu60Hf30Ti10 alloy, suggesting that the former comprises a higher fraction of the amorphous phase than the latter. Both powders showed distinct glass-transition with a large super-cooled liquid region. Consolidation of Cu60Hf25Ti15 powder was carried out by means of spark-plasma sintering at applied pressures of 200 and 500 MPa, choosing a sintering temperature within the super-cooled liquid region (T = 753 K). The sintered compacts exhibited some pores and interparticle boundaries.

Abstract: The microstructure and properties of Cu-TiB2 composites produced by high-energy ball-milling of TiB2 powders and spark-plasma sintering (SPS) were investigated. TiB2 powders were mechanically milled at a rotation speed of 1000rpm for short time in Ar atmosphere, using a planetary ball mill. To produce Cu-xTiB2 composites( x = 2.5, 5, 7.5 and 10wt.% ), the raw and milled TiB2 powders were mixed with Cu powders by means of a turbular mixer, respectively. Sintering of mixed powders was carried out in a SPS facility under vacuum. High-energy ball-milling resulted in refinement of TiB2 particles. XRD patterns of milled TiB2 powders indicated broader TiB2 peaks with decreased intensities. After sintering at 950
for 5min using the raw and milled TiB2 mixture powders, the sintered density decreased with increasing TiB2 content regardless of milling of TiB2. In the case of raw TiB2, hardness rapidly increased from 4 to 44 HRB with increasing TiB2 content. The electrical conductivity changed from 95.5 to 80.7 %IACS. For mixtures of Cu powders with milled TiB2 powders, hardness increased from 38 to 67 HRB as TiB2 content increased, while the electrical conductivity varied from 88% to 51 % IACS. When compared to compacts sintered with raw and milled TiB2 powders, the electrical conductivity of specimens with raw TiB2 powder was higher than that of specimens with milled TiB2 powder, while hardness was slightly lower.