Materials Science Forum Vols. 449-452

Abstract: Transformation behaviors and shape memory characteristics of Ti-45Ni-5Cu alloy ribbons fabricated by melt spinning were investigated by means of optical microscopy, differential scanning calorimetries(DSC), X-ray diffraction and thermal cycling tests under constant load. They depended largely on temperatures of liquid metal. The B2-B19-B19’ two-step transformation occurred in the ribbons fabricated with the liquid whose temperature was higher than 1723 K, while the B2-B19’ one-step transformation occurred in the ribbons with the liquid at 1673 K. The stabilization of the B19 martensite in Ti-45Ni-5Cu alloy ribbons was ascribed to the high density of dislocations which made strong resistance to large lattice deformation associated with a formation of the B19’ martensite.

Abstract: Porous TiNi shape-memory alloy (TiNi SMA) bodies were produced from the (Ti+Ni) powder mixture by self-propagating high-temperature synthesis (SHS) method. Various processing variables such as ignition temperature and heating schedule were used to control the pore structure. Relationship between pore structure and mechanical property was also investigated. An in vivo test was performed to evaluate bone tissue response and biocompatibility of porous TiNi SMA. It showed no apparent adverse reactions such as inflammation and foreign body reaction. Bone ingrowth was found in the pore space of all implanted blocks. Introduction Titanium-nickel intermetallic compound is well known as one

Abstract: Mechanically-alloyed NiAl powder was sintered by Spark-Plasma Sintering (SPS) process. Densification behavior and mechanical property were determined. Above 97% relative density was obtained after sintering at 1150oC for 5min. Crystallite size determined by the Scherrer method was approximately 80 nm. TEM observation revealed a relative larger crystallite size. X-ray diffraction analysis showed that the sintered bodies were composed mainly of NiAl phase together with Ni3Al phase. Sintered NiAl body showed an average Vicker’s hardness of 555Hv, transverse-rupture strength of 1393MPa, 4-point-bending strength of 1100MPa, and fracture toughness of 19.9MPa m-1/2

Abstract: Nano-crystalline CeO2 was synthesized by the mechanical milling and subsequent heat-treatment from the mixture of Ce(OH)4 as precursor, and NaCl as diluent. The diluent provided diffusion barrier during milling and heat-treatment, which was easily dissolved out by deionized water. The size of crystallite and the strain variance of CeO2 were depended on the temperature and heat-treatment time: increased with the temperature (400~700oC) and time (1~24 hours) increasing, and saturated near at 20nm in size owing to the densification of diluent. The synthesized nano-crystalline CeO2 powder was applied as an abrasive in CMP (Chemical Mechanical Planarization) slurry. When blanket-type SiO2 and Si3N4 wafers were polished with the slurries, the removal rates (RR) of SiO2 and Si3N4 wafers and selectivities (RRSiO2/RRSi3N4) were influenced by synthetic condition of abrasive, the suspension stability and the pHs of slurries.

Abstract: In order to control the grain size of Cu-15.0Zn-8.1Al shape memory alloy, the spark plasma sintering (SPS) technique was applied. The sintering processes were carried out under different atmospheres with a different powder size. The sintered bodies were denser under the Ar+4%H2 gas atmosphere than under the 100% Ar gas. By using the small-sized powders, the fine microstructure with average grain size of 2~3􀀀 was obtained. With the large-sized powders, the single martensitic phase was observed with the average grain size of 70~72􀀀 . When the starting powders with different sizes were mixed, it is confirmed that the average grain size of the manufactured alloys was 15􀀀 , but the distribution of grain size was not uniform.

Abstract: Microstructural change of TiB2-Cu nanocomposite during spark plasma sintering (SPS) was investigated. Under simultaneous action of pressure, temperature and pulse electric current titanium diboride nanoparticles distributed in copper matrix move, agglomerate and form a interpenetrating phase composite with a fine-grained skeleton. Increase of SPS temperatures and holding times promotes the densification of sintered compacts due to local melting of copper matrix.

Abstract: [SiO2]x[TiO2]1-x(x = 0.1, 0.2, 0.3, 0.4) powders were prepared by hydrothermal reaction of titanium isopropoxide (TIP) and tetraethyl-orthosilicate (TEOS) stabilized in acidic ethanol/water solution. The size and phase of TiO2 particles were controlled by adjusting the SiO2 content and the composition of the solvent system. The microstructure and photocatalytic activity of the prepared SiO2-TiO2 nanoparticles were characterized by XRD, TEM, BET, Raman and UV visible spectroscopic techniques. The major phase for all the prepared samples was anatase. The particle size of 0.3SiO2-0.7TiO2 powders prepared with excess amount of ethanol (REtOH = EtOH/alkoxide molar ratio = 120) was about 8.7 nm, while that of the sample prepared with small amount of ethanol (REtOH = 4) was 9.9 nm. The photocatalytic activity of these composite powders under excess ethanol was 1.5 times higher than that of pure TiO2 with respect to the decomposition of 1,4-dichlorobenzene (DCB).

Abstract: Bioactive ORMOSILS (organically modified silicate), PDMS-CaO-SiO2-P2O5 with five different P2O5 content (0, 0.01, 0.03, 0.06, 0.09 mol%) have successfully been synthesized by sol-gel process. The hybrids have been prepared with polydimethylsiloxane (PDMS), tetraethoxysilane (TEOS), calcium nitrate tetrahydrate [Ca(NO3)2
4H2O] and triethyl phosphate (TEP) as starting materials and subsequently soaked into the simulated body fluid (SBF) for different period of time and the bioactivity of hybrids was determined by examining the apatite formation on the surface of the specimen by FT-IR, Thin-Film X-ray Diffraction, and Scanning Electron Microscopy (SEM). All of the prepared samples with different P2O5 content showed in vitro bioactivity. It was observed that the increase in P2O5 content up to 0.03 mole % increases the apatite formation compared to P2O5- free hybrids. However, further increase in P2O5 concentration slows down the formation of the apatite layer most probably due to the decrease of pH of SBF by dissolution of a large amount of phosphate ions.

Abstract: The sintered microstructure homogeneity of W-15wt%Cu nanocomposite powders prepared from W-CuO mixture was investigated. The increment of heating rate considerably affected the homogeneity of sintered microstructure. In case of the higher heating rate, the microstructure was more homogeneous than that of the lower heating rate by reason of Cu- exudation during heating-up process.

Abstract: Al2O3 compacts with various phases were prepared by hydrolysis and spark plasma sintering (SPS) process of Al powder. The bayerite (
-Al(OH)3) phase was derived by hydrolysis of commercial Al powder with micron size, whereas the bohemite (AlO(OH)) phase was obtained by hydrolysis of nano Al powder synthesized by pulsed wire evaporation (PWE) method. Compaction as well as dehydration of both bayerite and bohemite was carried out simultaneously by SPS method, which is used to fabricate nano powder into dense compacts with a rapid heating rate of about 100 °C per min. under the pressure of 50 MPa. After compaction in the temperature ranges from 350 °C to 1100 °C, the bayerite and bohemite phases change into various alumina phases depending on the compaction temperatures. The bayerite shows the phase transition of Al(OH)3  -Al2O3  -Al2O3  -Al2O3 sequences. On the other hand, the bohemite experiences the phase transition from AlO(OH) to
-Al2O3 at 350 °C showing AlO(OH) 
-Al2O3  -Al2O3  -Al2O3  -Al2O3 sequences.