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Repeated deformation behaviors of 10 different X60 based steels were investigated in this study. At room temperature, repeated deformation tests were conducted with f=0.2 Hz, sinusoidal wave form and Δεta (total strain amplitude) = 0.9%, which are conditions similar to those for coiled tubing application. Different alloys whose microstructures were varied with addition of alloying elements showed different fatigue life. In particular, X60 steel modified by addition of titanium had superior fatigue properties than the base X60 steel. To clarify the relationship between repeated deformation life and microstructure, morphologies of the fractured surfaces and crack propagation path were examined. Most of the cracks propagated smoothly along the ferrite-ferrite interface or through the ferrite, while the crack path was largely changed by pearlite phases, which were relatively harder phases than ferrite. Based on those results, we related the microstructure parameters to repeated deformation behavior.

keyword : alloys, rolling, fatigue, SEM, X60 based steels

The extrudability and mechanical properties of the Mg-7Sn-1Al-1Zn (TAZ711) alloy were investigated by performing indirect extrusion at various temperatures and speeds and tensile tests and comparing the results with those of the Mg-8Al-0.5Zn (AZ80) alloy. When the AZ80 alloy was extruded at a high extrusion temperature of 450 ℃ or at extrusion temperatures above 350 ℃ with a high extrusion speed of 12 m/min, surface hot cracking occurred, while the TAZ711 alloy was successfully extruded without any surface defects at a high temperature of 450 ℃ with a high speed of 12 m/min. With an increasing extrusion temperature and speed, the average grain size of the extruded AZ80 and TAZ711 alloys increased and the yield and tensile strength decreased. The TAZ711 alloy had a higher yield strength and lower tensile strength and elongation than the AZ80 alloy extruded under the same conditions.

keyword : metals, extrusion, mechanical properties, optical microscopy, extrudability

Abstract: The damping capacity of high manganese austenitic stainless steel with a two phase mixed structure of deformation-induced martensite and reversed austenite was studied. Reversed austenite with an ultra-fine grain size of less than 0.2 μm was obtained by reversion treatment. The two phase structure of deformation-induced martensite and reversed austenite was obtained by annealing treatment at a range of 500-700℃ and various times in cold rolled high manganese austenitic stainless steel. The damping capacity increased with an increasing annealing temperature and time. In high manganese stainless steel with the two phase mixed structure of martensite and austenite, the damping capacity decreased with an increasing volume fraction of deformation-induced martensite. Thus, the damping capacity was strongly affected by deformation-induced martensite. The results confirmed that austenitic stainless steel with a good combination of strength and damping capacity was obtained from the two phase mixed structure of austenite and martensite.

keyword : reversed austenite, deformation induced martensite, damping annealing, transmission electron microscopy, metals

Abstract: Carbon diffusion of ultra-low carbon steel treated at 930℃ for 10, 30, 60 and 120 minutes is investigated by using optical microscopy, EPMA and Micro Vickers. Results of experiment and finite element analysis are compared. The carbon diffusion seen in the optical microscopy, EPMA and Micro Vickers test increased as the time treated at 930 ℃ increased. Such phenomena is explained by finite element analysis.

keyword : hot press forming, carbon diffusion, ultra low carbon steel, finite element analysis

This study investigates the effect of surface roughness on bonding interface properties, such as micro hardness, diffusion layer thickness, intermediate phases, bonding strength, etc., in hot pressed Cu/Al clad material for electric conductors. Different surface roughnesses at the bonding surfaces of oxygen free copper (OFC) and Al 1050 matrix materials were obtained by emery paper grinding and buff polishing. The Cu/Al clad materials were prepared by hot-pressing under 200 MPa at 450 ℃ for 15 min. Microstructures of the Cu/Al interfaces were observed using an optical micrograph (OM), a Field Emission Gun-Scanning Electron Microscope (FEG-SEM) and an Energy Dispersed X-ray Analyser (EDX) in order to investigate the effects of surface roughness on the bond properties of the Cu/Al clad materials. A shear fracture test was performed to evaluate the bonding strengths of the Cu/Al clad materials. A Micro Knoop hardness test was used to measure the micro hardness in the diffusion layer at the Cu/Al interface. The 3-layer diffusion layer was observed at the Cu/Al interfaces. The thickness of the diffusion layer decreased and an additional intermediate phase ξ2 was formed with the increase of surface roughness. The Micro Knoop hardness increased rapidly mainly due to the formation of η2 and ξ2 phases and then decreased gradually with the increase of surface roughness. The bonding strength of the Cu/Al interface increased rapidly in the initial stage and increased slowly up to the peak value and then decreased slightly with the increase of surface roughness. The shear fracture surfaces of the Cu/Al bonding interface were flat and had an even shape in the sample with a low surface roughness, but had a rough and uneven shape in high surface roughness conditions.

keyword : composites, surface roughness, joining, interfaces intermetallics, scanning electron microscopy

Silver nanorods were fabricated using a porous anodic aluminum oxide (AAO) template by an ink-jet printing process. The highly arrayed AAO template was prepared to infiltrate silver nano particles by an anodization method. The ink-jet printing unit is equipped with a piezoelectric nozzle with a 50 um orifice from Microfab technology. The morphology and crystal structure of the silver nanorods were confirmed by field emission scanning electron microscopy and x-ray diffraction pattern, respectively. The diameter of the silver nanorods was about 60 nm, which was consistent with that the diameter distribution of the AAO template.

keyword : nanorods, AAO, porous alumina, nano ink, ink jet printing, anodizing

Samples with a composition of 80 wt% Mg-14 wt% Ni-6 wt% NbF5 (denoted as Mg-14Ni-6NbF5) were prepared by reactive mechanical grinding, and the hydriding and dehydriding properties of the specimens were then examined. The activation of Mg-14Ni-6NbF5 was completed after two hydriding (under 12 bar H2)-dehydriding (in vacuum) cycles. Mg-14Ni-6NbF5 had a hydrogen storage capacity of about 5.5 wt% H. At the number of cycles n = 2, the sample absorbed 4.93 wt% H for 5 min, 5.20 wt% H for 10 min, and 5.48 wt% H for 60 min at 573 K under 12 bar H2, and desorbed 0.58 wt% H for 10 min, 1.52 wt% H for 30 min, and 2.47 wt% H for 60 min at 573 K under 1.0 bar H2. The hydriding rate increased as the temperature increased from 423 Kto 573 K since the effect of acceleration of thermally activated process predominates, and decreased from 573 K to 623 K since the effect of decrease in the driving force for the hydriding reaction predominates. NbF5 formed MgF2 and NbH2 by the reaction with Mg and hydrogen. Mg-14Ni-6NbF5 exhibited a higher hydriding rate than both Mg-10NbF5 and Mg-14Ni-6Fe2O3.

keyword : hydrogen absorbing materials, mechanical alloying/milling, scanning electron microscopy, X-ray diffraction, Ni and NbF5 addition

The temperature of the MPCB of a 16-chip LED package (TB) was kept at 25℃, 50℃ and 75℃ using a Peltier element and compared with natural cooling conditions. The junction temperature (TJ) was measured by a thermal transient method. A heat transfer model is proposed to investigate the heat flux through the three heat dissipation paths, upward, sideward and downward, and to predict the temperature distribution inside the LED package. The results showed that, with 4.8 W of input power applied, TJ decreased dramatically from 115℃ to 38℃ by keeping TB at 25℃ due to the elimination of the heat convection resistance at the MPCB surface. It was predicted that a maximum of 28 W could be applied to the package by keeping TB at 25℃ under the constraint condition that the junction temperature of the LED not exceed 100℃.

keyword : optoelectronic materials, thermomechanical processing, thermodynamic properties, thermal analysis, thermal transient analysis

A detachable working electrode on different counter electrodes without sealing is proposed for dye-sensitized solar cells (DSSCs) to reduce the time needed for characterizing the photovoltaic properties. The photovoltaic properties were measured with time immediately after injecting the electrolyte and with the number of repetitions of reassembling the DSSC devices. The photovoltaic properties, such as the current density, open circuit voltage, fill factor, and energy conversion efficiency (ECE), were measured using a solar simulator apparatus. The microstructure was examined by optical microscopy. The ECE was checked every two minutes immediately after electrolyte injection. The photovoltaic properties were determined reliably at 10-20 minutes after electrolyte injection due to a trade-off between the diffusion of the electrolyte into the TiO2 layer and the degradation of the electrolyte with time. With the repetition of reassembly, the detachable electrodes might show a reliable ECE until four repetitions. ECE degraded abruptly after five repetitions of the test because of the broken TiO2 layers and spacers. These results suggest that the proposed detachable electrodes without sealing will be suitable for repeated measurements for photovoltaic properties.

keyword : solar cells, recycling, optical properties, optical microscopy, reliability

Abstract: Transparent and conductive Indium Tin Oxide (ITO) thin films were prepared on glass substrates at room temperature (RT) by a RF magnetron sputtering method. The ITO films sputtered at room temperature had an amorphous structure and uniform surface morphology with low planner density. We report the influence of rapid thermal annealing (RTA) treatment on the microstructure, optical and electrical properties of the ITO thin films. Rapid thermal annealing (RTA) was carried out for 2 min, 4 min, 5 min, 8 min and 10 min at 500 ℃ in 98%N2 + 2%H2 ambient gas. This study provides data about the microstructure and optical properties of ITO thin films with thicknesses of around 100 nm. The experimental results showed that the post growth RTA temperature has a significant effect on the properties of ITO thin films. The preferred orientation along the (222) plane, and the average grain size, measured from TEM micrographs, ranged from 5 to 30 nm. The average optical transmittance in a wavelength range of 200-800 nm increased from 74% to 88% after rapid thermal annealing at 500 ℃, where the highest value of the figure of merit was obtained. The resistivity decreased by 500 ℃ at 5 min, which was the annealing temperature, and after that the resistivity increased. The major factor of the resistivity change was the change of the carrier concentration. In addition to the increase in carrier concentration, RTA at 500 ℃ at 5 min caused the band gap energy of the ITO thin films to rise linearly.

keyword : ITO, rapid thermal annealing, RF magnetron sputtering, transparent conducting film