Materials Science Forum Vol. 750

Abstract: Ti metal matrix composites (Ti–MMCs) reinforced by vapor grown carbon nanofiber (VGCF) and graphite particle (Gr) were prepared via powder metallurgy and hot extrusion. Ti with 0~0.4wt% VGCF/Gr mixture powders were consolidated by using spark plasma sintering (SPS) at 800 °C. Hot extrusion was then performed at 1000 °C with an extrusion ratio of 37:1. Microstructures and mechanical properties of the as-extruded Ti composites were investigated. Tensile strength of Ti–VGCF/Gr composites was steadily augmented when additions of VGCF/Gr were increased from 0.1 to 0.4 wt%. YS and UTS were increased 40.2% and 11.4% for Ti–0.4wt%VGCF as compared to pure Ti, while those values were 30.5% and 2.1% for Ti–0.4wt%Gr. The strengthening mechanism including grain refinement, carbon solid solution strengthening and dispersion hardening of TiC/carbon was discussed in detail.

Abstract: A systematic series of experiments was performed to determine the optimum firing schedule of Y2O3. A two-step sintering with subsequent profile succeeded to fabricate Y2O3 ceramic with the relative density of 97.6% and the average grain size of 0.46 μm: first step and second step temperature of T1 = 1490 °C and T2 = 1350 °C, respectively and second step holding time of t2 = 20 h. After the firing schedule of pure Y2O3 was determined, two types of TiO2/Y2O3 and ZrO2/Y2O3 composites were fabricated for the further improvement of mechanical properties. According to results, ZrO2/Y2O3 composite showed a dramatic increase in strength and toughness as 417 MPa and 4.4 MPa.m1/2, respectively.

Abstract: Y_1-xGd_xBa₂Cu₃O_7-y film with BaZrO₃ was fabricated on CeO₂ buffered LaMnO₃/ion beam assisted deposition MgO/Gd₂Zr₂O₇/Hastelloy C276^TM substrates by the trifluoroacetates metal organic deposition process, whose microstructural and elemental analyses were performed by transmission electron microscopy. Y_1-xGd_xBa₂Cu₃O_7-y film with the thickness about 700 nm was found composed of c-axis oriented grains and large numbers of randomly oriented precipitates, such as (Y,Gd)₂Cu₂O₅, CuO and BaZrO₃. (Y,Gd)₂Cu²O⁵ and CuO precipitates were heterogeneously dispersed in the Y_1-xGd_xBa₂Cu₃O_7-y matrix with their sizes ranging between 100 and 200 nm, and BaZrO₃ precipitates were uniformly dispersed with their sizes ranging between 10 and 20 nm. Electron tomography with elemental information was performed further to reveal the three-dimensional information of BaZrO3 precipitates.

Abstract: Using gas-atomized Ti-based metallic glassy powder, or the mixed powder blended with hydroxyapatite (HA) powder, we produced Ti-based bulk metallic glasses (BMGs) and the composites with high strength and satisfying large size requirements by a spark plasma sintering (SPS) process. The Ti-based BMGs and the composites with excellent properties and without toxic elements make it possible to apply as biomedical materials.

Abstract: Many studies have focused on the fabrication of Cu nanowires, because of their potential applications in diverse fields such as nanoelectronics and gene delivery. In this study, we successfully fabricated Cu nanowires by electrochemical deposition method. Cu nanowires was synthesized by electroplating from a 0.4M CuSO₄ bath, and the current was 0.005A. The length of nanowires can be controlled via deposition time and current. After depositing for 60 minutes, the length of the nanowires is approximately 10 µm. Serum coated and non-coated nanowires with the concentration of 10², 10³, 10⁴ and 10⁵ were added to 96-well cell culture plate in which mesenchymal stem cells were pre-seeded. After incubating for 3 days, cytotoxicity of nanowires was measured with MTT assay method. Results indicated that cytotoxicity increased as the increase of nanowires concentration. Serum coated nanowires had higher cell viability as compared with the non-coated group.

Abstract: The electrochemical behavior of a new magnesium alloy (AZ61) containing rare earth elements-cerium (Mg-Al-Zn-Mn-Ce alloys) was investigated in 3% NaCl electrolyte using electrochemical methods such as linear sweep voltammetry, Tafel curves and electrochemical impedance spectroscopy. Scanning electron microscopy was used to characterize the surface morphologies of magnesium and its alloys. The results shows that compared with that of the most commonly used Mg alloy–AZ61, the cerium containing magnesium alloy exhibited higher electrochemical activity, and higher corrosion resistance. The electrochemical activity of Mg-Al-Zn-Mn-Ce was higher than that of Mg and Mg-Al-Zn-Mn-Ce alloys in 3% NaCl. The corrosion resistive order decreased in the following sequence: Mg-Al-Zn-Mn-Ce > Mg-Al-Zn-Mn > Mg. The electrolytes favored anodic magnesium oxidation, but the alloying element of Ce facilitated the formation of dense passive films on alloy surfaces.

Abstract: In this paper, the established control system and its control algorism of a new twin roll strip caster developed by authors is presented. It is illustrated the roll-gap control strategy of the twin roll strip caster based on a feed forward-feedback system. From the experimental results, the susceptibility of control convergence time, stable and accurate are shown on a higher level than traditional control strategy.

Abstract: The effect of acid and alkali leaching on catalytic activity of an atomized Ni₃Al powder for methanol decomposition was investigated. It was found that a two-step process, an acid leaching followed by an alkali leaching, was most effective for improving the activity. The optimal conditions of acid and alkali leaching were examined. The effect of the acid and alkali leaching was attributed to the formation of fine Ni species and a porous surface structure.

Abstract: Nanoporous copper (NPC) was fabricated through dealloying nanocrystallized Ti_{Subscript text}50Cu50 ribbon alloy under a free immersion condition in HF solutio_{Subscript text}ns at 25 °C. Multimodal nanoporous structure was formed due to the presence of Ti3Cu4 phase, which was co-precipitated with Ti2Cu during the heat treatment at T = 400 °C (Italic textT_{Subscript text}g Italic textT Subscript textx). The presence of multiphases in tItalic texthe starting material caused the different behavior in the evolution of nanoporosity. In 0.03 mol/L HF solution, the bimodal nanoporous copper with a pore size of 54 nm and 184 nm was obtained in different regions where the composition differed. The ligament scale lengths in two regions were confirmed to be 54 nm and 203 nm, respectively. In 0.13 mol/L HF solution, the difference in the pore size and phase separation became weak, accompanying with the evolution of larger pores and smaller ligaments. The residue after dealloying was confirmed to be fcc Cu, indicated by the presence of Cu (111), (200), (220) and (311) in XRD patterns and TEM selective area diffraction pattern. The microstructure of the starting materials for dealloying, such as intermetallic phases, played a key role in the formation of the final multimodal nanoporous structure.

Abstract: At room temperature the macroscopic tensile behavior of TiAl alloys is extremely microstructure sensitive. In general the microstructures of TiAl alloys are heterogeneous at micro and meso scale. The materials micromechanisms that occur at different length scale have to be linked for a proper understanding of the macroscopic response. In order to explore those micromechanisms, methodologies combining advanced experimental and computational analysis have been proposed. Linking microstructure and properties using a two-scale numerical model we are able to explain the stress-strain and hardening behavior of this alloy.