Chuen-Guang Chao

Effects of volume fraction of reinforcement on tensile and creep properties of in-situ TiB/Ti MMC

In this study, the TiB/Ti composites with 5, 10 and 15 vol.% in-situ TiB were produced by melting route assisted with combustion synthesis. The main objective of present work was to investigate the effects of volume fraction of TiB on mechanical behaviors, in particular on creep properties. The dependence of tensile properties on the volume fraction of TiB resulting in morphology change was present, and the creep behaviors of TMC relating to the mechanism were evaluated and discussed.

In situ fracture observation of a TiC/Ti MMC produced by combustion synthesis

Combustion synthesis involving exothermic chemical reactions has been widely utilized to fabricate various in situ metal matrix composites (MMC) during the past decade. Recently, an in situ SEM observation has been performed to investigate the fracture behavior in a variety of MMCs prepared by conventional processes. However few papers about the in situ SEM observation on fracture behavior have been reported in the combustion-synthesized MMC. In the present study, a combustion-synthesized TiC/Ti MMC was fabricated for examining the fracture behavior using in situ SEM observation. The purpose of this paper is twofold: (1) the influence of reinforcement characterization on fracture behavior, including particle size, aspect ratio and interfacial chemistry and (2) the comparison of similarity/disparity of fracture processes between combustion-synthesized and conventional MMCs.

The influence of magnesium on carbide characteristics and creep behavior of the Mar-M247 superalloy

In recent investigations, it has been shown that the microaddition of Mg in wrought superalloys significantly enhances stress rupture life, ductility and fatigue endurance at elevated temperatures. These improvements are mainly associated with carbide refinement arising from segregation of Mg to GB and carbide/matrix interface. Although, some studies related to Mg segregation phenomenon have been carried out, the true mechanisms are not fully understood. Furthermore, little work has been reported in introducing Mg as a microalloying element in cast superalloys which are normally poor in ductility and toughness at both room and elevated temperatures. On this basis, Mar-M247 superalloy was chosen for the first time in this work for studying the influence of Mg microaddition on high temperature properties. The objectives of present study were to determine the microstructural characteristics and to investigate the creep behavior of Mar-M247 superalloy due to the microaddition of Mg, particularly in ductility. In addition, some available mechanisms associated with the microstructure change and property enhancement were discussed in this paper.

High-Reliability Ta2O5 Metal–Insulator–Metal Capacitors with Cu-Based Electrodes

The properties of tantalum oxide (Ta 2 O 5 ) metal-insulator-metal (MIM) capacitors with Al/Ta/Cu/Ta bottom electrodes were investigated. An ultrathin Al film successfully suppresses oxygen diffusion in the Ta 2 O 5 MIM capacitor with the Cu-based electrode. The electrical characteristics and reliability of Ta 2 O 5 MIM capacitors are improved by addition of ultrathin Al films. Ta 2 O 5 MIM capacitors have low leakage current density (1 nA/cm 2 at 1 MV/cm) and high breakdown field (5.2 MV/cm at 10 -6 A/cm 2 ). The decrease in leakage current is attributed to the formation of a dense and uniform Al 2 O 3 layer, which has self-protection property and stops further oxygen diffusion into the tantalum contact. The dominant conduction mechanism of leakage current is the Poole-Frenkel effect at electric fields above 1.5 MV/cm.

Nanoparticles of Pb–Bi Eutectic Nucleation and Growth on Alumina Template

A novel and convenient method of thermo-immersion was used to fabricate of a large of lead–bismuth (Pb–Bi) eutectic nanoparticles on an uniform size anodic aluminum oxide (AAO) template. The AAO with a 60 nm pore diameter was used as a template for nanoparticles nucleation and growth. Both Pb–Bi and AAO were placed in a glass tube in vacuum at 10-6 Torr, controlled by a molecular turbo pump then heated up to the melting point of the alloy. Nanoparticles nucleated and grew on the AAO template when the molten Pb–Bi solidified. The nanoparticles nucleated on the pore corners of the AAO template initially, grew simultaneously and assembled into a big nanoparticle on top of the AAO template later. Additionally, the size diameters of the initial nanoparticles were approximately 15 nm on the pore corners of the AAO template, and 80 nm when the initial nanoparticles formed a large nanoparticle. Latent heat was released when the molten Pb–Bi solidified to form nanoparticles. The size diameters distribution of nanoparticles was observed by scanning electron microscopy (SEM) such that, the diameters of the nanoparticles were 80 nm on top of the AAO template, and 200 nm in depths of the concave.

Improving Electrical Properties and Thermal Stability of (Ba,Sr)TiO3 Thin Films on Cu(Mg) Bottom Electrodes

Cu(Mg) alloy films have replaced pure Cu as bottom electrodes for (Ba,Sr)TiO3 (BST) capacitors used in high-frequency devices. A combined BST/Cu(Mg) structure reduced the leakage current density to 3.0×10-8 A/cm2 at 1 MV/cm, and increased the breakdown field from 0.4 to 2.4 MV/cm at 10-6 A/cm2, from the corresponding values of the BST/Cu structure. High-quality characteristics probably follow the formation of a self-aligned MgO layer following the deposition of a Cu(Mg) alloy by annealing in an oxygen ambient, yielding an electrode with an excellent diffusion barrier and electrical characteristics, which is therefore effective in a BST thin-film capacitor. Additionally, the bias temperature stress and time-dependent dielectric breakdown in ambient nitrogen at an electric field of up to 2 V at temperatures between 100 and 200 °C were considered to accelerate Cu+ ion drift.

Template assisted fabrication of tin nanospheres by thermal expansion and rapid solidification process

Tin (Sn) nanospheres with diameters ranging from 100 to 300 nm were fabricated by thermal expansion and rapid solidification process. The Sn melt was injected into an anodic aluminum oxide (AAO) template to form Sn nanowires. The Sn nanowire and AAO composite was then heated to the Sn melting temperature (~232°C) and quenched to low temperature (8°C). The Sn melt exhibits high surface tension and AAO has nanoscale roughness on its surface. These two properties caused Sn nanospheres to form easily on the AAO surface when the partial Sn melt expanded out from AAO channels and rapidly solidified on the AAO surface.

Improving Electrical Characteristics of Ta ∕ Ta2O5 ∕ Ta Capacitors Using Low-Temperature Inductively Coupled N2O Plasma Annealing

The electrical characteristics of Ta/Ta 2 O 5 /Ta capacitors are improved by treatments with inductively coupled N 2 O plasma. A low-temperature (250°C) and short (5 min) process was used to reduce the leakage current and improve the reliability. A low leakage current density (4.0 X 10 -10 A/cm 2 under 1 MV/cm), high breakdown field (4.2 MV/cm at 10 -6 A/cm 2 ), and lifetime of over 10 years at 1.61 MV/cm is obtained for the Ta/Ta 2 O 5 /Ta capacitor with the inductively coupled N 2 O plasma treatment. The conduction mechanism of the leakage current in the Ta/Ta 2 O 5 /Ta capacitor is discussed using current-voltage analyses and shows that the leakage current of the Ta/Ta 2 O 5 /Ta capacitor is dominated by Schottky emission. N 2 O plasma treatment can effectively reduce oxygen vacancies and the surface roughness of the Ta 2 O 5 film, inhibiting the conduction of the leakage current.

Microstructure and properties of Pb nanowires fabricated by casting

In this study, we fabricated Pb nanowires in porous alumina membranes with different diameters by pressure casting. It can produce a large quantity of Pb nanowires with average diameters of 20, 80, 200, and 300 nm and lengths of up to 10 mm. The diameter and length of the nanowires can be controlled by selecting templates with a desired size. The microstructure and size effects of Pb wires on the solidification process were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and thermal analysis. The nanowires with average diameters of 20 and 80 nm were single crystals, but those with average diameters of 200 and 300 nm were polycrystals. Finally, we also discussed the melting behaviors of the Pb nanowires in the porous alumina matrix. [DOI: 10.1143/JJAP.47.4815]

Formation procedure and microstructural analysis of Pb7Bi3 (Pb-Bi) alloy nanowires

Pb7Bi3 nanowires with a diameter of 80 nm have been fabricated by a centrifugal process, in which the Pb–Bi alloy nanowires formed as the melt was forced into the pores of an anodic aluminum oxide (AAO) template. The nanowires inside the pores of the anodic alumina template could be separated from the remaining metal by a quenching process. X-ray diffraction analysis and energy dispersive X-ray spectroscopy were carried out to determine the composition of the lead-bismuth alloy nanowires. Selected-area electron diffraction and high-resolution electron microscopy investigations indicate that the Pb–Bi alloy nanowire is a single crystal without dislocations and has a hexagonal structure.