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Titanium and its alloys offer the highest strength, excellent corrosion resistance and the highest strength to weight, but their disadvantage is a higher cost. This study was made to obtain useful information on their high-strength properteis for designing beta type titanium alloys using the DV-Xα method. To lower prices low-cost elements (Mo, Al, Fe) were used. The Mechanical properties of these alloys are compared to commercial alloys in order to investigate the characteristics of the alloys. The results showed strength of the titanium alloys was somewhat higher (30-90 MPa) than conventional alloys.

keyword : titanium alloys, alloy design, DV-Xα method, mechanical propeties, tensile test

The effects of cooling rates from 400 to 200℃ on hydride reorientation were investigated using ring specimens of 250 ppm and 500 ppm H Zr-Nb cladding tubes. For no stress conditions with cooling rates of 2.5 and 25.0℃/min, the 250 ppm H specimens show that hydride plates are reprecipitated only in a circumferential direction during the cooling from 400 to 200℃, but the hydride plates appear to be much shorter for the 25.0℃/min cooling rate. However, the 500 ppm H specimens show that hydride plates are reprecipitated as a mixture of circumferential and radial hydride plates for the 25.0℃/min cooling rate. This mixed hydride plates may be caused by a blocking effect of circumferential hydrides undissolved on the one hand and by a considerable tensile hoop stress locally generated by a large difference in the cooling rates between outer and interior layers on the other hand. For 150 MPa tensile hoop stress conditions with a cooling rate of 2.5℃/min, the 500 ppm H specimens show a relatively shorter radial hydride plates than the 250 ppm H specimens, which may be explained by a blocking effect of undissolved circumferential hydride plates in the 500 ppm H specimens. Tensile tests for the specimens experiencing the cooling from 400 to 200℃ under the 150 MPa hoop stress conditions indicate that there is little impact of hydrogen content on ultimate tensile strengths but the 250 ppm H specimens generate less plastic elongation and more noticeable cleavage fracture than the 500 ppmH specimens, which may be caused by relatively longer

keyword : hydride, alloy, deformation, ductility, tensile test

As-received Zr-Nb cladding tubes and 600 ppm hydrogen-charged tubes were employed to evaluate the effects of cladding cooling rates on the extent of hydride reorientation from circumferential hydrides to radial ones and mechanical property degradations with the use of cooling rates of 2, 4 and 15℃/min from 400℃ to room temperature simulating cladding cooling under interim dry storage conditions. The as-received cladding tubes generated nearly the same ultimate tensile strengths and plastic elongations, regardless of the cooling rates, because of a negligible hydrogen content in the cladding. The 600 ppm-H cladding tubes indicate that the slower cooling rate generated the larger radial hydride fraction and the longer radial hydrides, which resulted in greater mechanical performance degradations. The cooling rate of 2℃/min generates an ultimate tensile strength of 758 MPa and a plastic elongation of 1.0%, whereas the cooling rate of 15℃/min generates an ultimate tensile strength of 825 MPa and a plastic elongation of 15.0%. These remarkable mechanical property degradations of the 600 ppm-H cladding tubes with the slowest cooling rate may be characterized by cleavage fracture surface appearance enhanced by longer radial hydrides and their higher fraction that have been precipitated through a relatively larger nucleation and growth rate.

keyword : metals, hydrogen absorbing materials, thermomechanical processing, mechanical properties, microstructure

In this study, the microstructural evolution of CoNiCrAlY-YSZ duplex coating manufactured by electron beam physical vapor deposition (EB-PVD) was investigated in terms of surface and cross-sectional morphology, local distribution of alloying elements and constitutive phases. A defect-free, well-bonded CoNiCrAlY coating was formed at substrate temperatures beyond 600℃. A higher substrate temperature promoted the growth or coalescence of CoNiCrAlY columnar grains, resulting in a rougher surface. Non-uniform distribution of alloying elements in the CoNiCrAlY coating occurred along the coating thickness, which was mainly attributed to the different equilibrium vapor pressure of the alloying elements. Both CoNiCrAlY and YSZ coatings formed a well-defined columnar grain structure which grew in the direction perpendicular to the substrate surface.

keyword : CoNiCrAlY-YSZ, alloys, vapor deposition, microstructure, transmission electron microscopy

The Ni-based superalloy, Inconel 713, was corroded between 800 and 1100℃ for up to 100 h in an Ar-1% SO2 atmosphere. It displayed good corrosion resistance, because the corrosion progressed mainly via oxidation rather than sulfidation. The corrosion products were α-Al2O3, Cr2O3, TiO2, NiO, NiAl2O4, and NiCr2O4. Sulfur was sometimes weakly segregated around the scale-alloy interface. Preferential oxidation occurred along the grain boundaries of the matrix. Except in these areas, uniform oxidation occurred, forming thin scales. The formed scales were prone to spallation.

keyword : alloys, casting, corrosion, oxidation, scanning electron microscopy, IN 713 superalloy

In order to investigate the high temperature deformation behaviors of TiC0.98, crystals were grown by the radio frequency (r.f.) floating zone technique and were deformed by a compression test at temperatures from 1283 to 2133 K and a strain rate from 5.87 × 10-4 to 6.01 × 10-3s-1. TiC0.98 exhibited a marked work-softening phenomena which is characteristic of covalently bonded materials such as Ge and Si, and the phenomena became less clear with an increasing temperature and with a decreasing strain rate. After the softening, work hardening was observed. The rate hardening decreased as the temperature increased. The stress-strain curve can be explained in terms of the increase in the athermal internal stress and the decrease in the thermal effective stress with the increase in dislocation density by the deformation. The upper yield stress was mainly determined by the frictional resistance to dislocation motion, and the athermal internal stress contribution was very small.

keyword : ceramics, deformation, mechanical propeties, compression test, work-softening

The heat sink in LED chips has been a major challenge for high-power LED module design. Elevated chip temperatures cause adverse effects on LED performance, lifetime, and color. An insulated metal substrate (IMS) is the commonly used substrate and has good thermal performance and low cost. This study used an aluminum IMS with good heat radiation efficiency to solve these problems. The most traditional IMS technique is electrochemical anodization. There are various methods to form electrical conductors on anodized aluminum. In this study, the anodization process was performed on an aluminum substrate using a phosphoric acid electrolyte to form the AAO layer. This investigation confirmed that electroless Ni-P plating for seed layers could be used to substitute for the Cu-sputtering process. Our evaluation of the reliability of the different thicknesses of aluminium anodic oxidation and the electro-plated Cu electrode revealed that the maximum peel strength was 1.6 kgf/cm and it was obtained at an anodizing time of 1000 minutes. The TCT, the solder shock test and the solderability test showed that the substrates were not delaminated.

keyword : nanostructured materials, anodization, anodic aluminum oxide, light emitting diode

ZnO nanorods were grown by a hydrothermal method on ZnO seed layers that had previously been prepared from solutions containing various precursor concentrations. The effects of the ZnO seed layers prepared with various precursor concentrations on the structural and defect emissions of the ZnO nanorods were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy. The surface morphology of the ZnO seed layers changed with an increasing precursor concentration, and the diameters and densities of the ZnO nanorods depended on the morphologies of the ZnO seed layers. The ZnO seed layers prepared with various precursor concentrations affected the residual stress in the nanorods grown on the seed layers, the intensity and full widths at half maximum of the 2-theta angle in the XRD spectra for the nanorods, and the intensity and position of the defect emission peak in deep-level emission (DLE) PL spectra for the ZnO nanorods.

keyword : semiconductors, sol-gel, optical properties, x-ray diffraction, seed layers, ZnO

The aim of this article is to elucidate the influence of reduction ratio during roll bonding on the microstructural evolution, mechanical properties and room-temperature formability of Al-Cu 2-ply clad metal. The evolution of the interface microstructure was first characterized by a scanning electron microscope (SEM) and transmission electron microscope (TEM) attached with energy dispersive spectroscopy (EDS). The presence of an intermetallic compound as well as severe grain refinement was detected at the interface of the Al-Cu bimetal fabricated under the highest reduction ratio of 65% adopted in this study. Taking into account the difference of the microstructure with a reduction the ratio, mechanical properties and bonding strength were then evaluated by uniaxial tensile and peel tests. It was observed that the bonding strength, elongation and tensile strength for Al-Cu 2-ply sheets were incomparably reduced by decreasing the reduction ratio during the roll bonding process, which directly correlated with the microstructural evolution at the interface. Moreover, the higher reduction ratio during the roll bonding, the more room temperature formability could be achieved for Al-Cu 2-ply sheet by applying both three-point bending and Erichsen tests.

keyword : composites, rolling, interfaces, tensile test, mechanical properties

In this research, a series of secondary warm rolling was performed under various process conditions in order to evaluate the influence of thermo-mechanical treatment on the interface microstructure and subsequent mechanical properties of roll-bonded STS/Al/Mg 3-ply laminates. The variation of interfacial microstructure was observed by scanning and transmission electron microscopes equipped with energy dispersive X-ray detector. Uniaxial tensile, hardness and drum peel tests were then carried out to clarify major mechanical properties of STS/Al/Mg clad sheets. We revealed that annealing for 60 min followed by secondary warm rolling at 300℃ under the reduction ratio of 20% could effectively improve the bonding strength at the Al/Mg joint and the tensile properties of roll-bonded STS/Al/Mg 3-ply laminates.

keyword : composites, thermomechanical processing, interfaces, tensile test, mechanical properties