Abstract: The effects of antimony and indium addition on wettability and interfacial reaction of Sn-3.0Ag-0.5Cu lead free solder on copper substrate were investigated. The experimental results showed the melting point of solder alloy containing 0.5 wt.% In and 0.5 wt.% Sb were slightly increased about 3.66°C. The pasty range of solder alloys were increased about 6°C while the undercooling of solder alloys were decreased. The microstructures of solder alloy were contained of In and Sb consists of Ag3Sn, Cu6(Sn,In)5, SnIn, Ag3(Sn,In) and SnSb intermetallic compounds (IMCs) dispersed on Sn-rich phase. The wettability of solder alloys were improved by increasing soldering times. In addition, the thickness of intermetallic compounds (Cu6Sn5) were obviously increased with increasing soldering times.
Abstract: This research work was aimed at studying creep of a slurry squeeze-cast ZA-27 zinc alloy. The Gas-Induced Semi-Solid (GISS) technique was used for preparing semi-solid metal slurry with two different solid fractions. The ZA-27 alloy slurry was squeeze cast to form plate-like specimens with dimension of 100×100×15 mm3. The tensile specimens were machined from the squeeze-cast plates and heat-treated before mechanical test. Tensile creep tests were performed at 140 °C, at stresses of 20, 40, 60 and 80 MPa, in an ambient air. Two groups of specimens, the low solid fraction ZA-27 alloy (GISS 5s) and the high solid fraction ZA-27 alloy (GISS 15s) were tested for comparison of creep property. The results show that the GISS 5s has longer creep life than the GISS 15s. The power-law creep stress exponents (n) of GISS 5s and GISS 15s are 1.45 and 1.04, respectively. Based on the creep stress exponents found from the present study, it could be concluded that at the temperature of 140 °C and stress between 20 and 80 MPa, creep of both alloys was governed by the diffusional creep mechanism.
Abstract: A Smart material can adapt to the external influences such as pressure, temperature, humidity, pH, electric or magnetic fields, an example is liquid crystal. Liquid crystal materials also can be applied for thermal mapping such as thermochromic liquid crystals (TLC) sheet. TLC sheet has a good response to the temperature changes which is shown by color play. This special characteristic of TLC can be used to explain some theoretical aspects of heat transfer on metals. The metals surface images during heating will be processed by converting the RGB images to the HSV images and then applied an edge detection method on hue images. From the thermal visualization, it can be shown that the largest heat exchange to the environment occurs at metal edges, so it is necessary to apply the heat insulator during the process of collecting data in block calorimeter experiments. The brass metal has the highest heat transfer rate, followed by copper and brass. It corresponds to the specific heat (c) of metals which csteel>ccopper>cbrass. Furthermore, it can be shown that since the heat starts to be evenly distributed until 300 seconds, the increasing of metals temperature is obtained ∆Tsteel<∆Tcopper<∆Tbrass and the increasing of mean hue (∆mean-hue) are obtained ∆mean-hue(steel)<∆mean-hue(copper)<∆mean-hue(brass). This result can be used to explain that in block calorimeter experiments, the measurement should be carried out after several minutes to obtain the even heat distribution across the entire metal surface.
Abstract: This paper presents study of a thermomechanical bimorph actuator, constituted by layers of polymer composite material. The proposed bimorph consists of polydimethylsiloxane (PDMS) and carbon black-polydimethylsiloxane (CB-PDMS) polymer composite layered structure. The thermomechanical response of the PDMS and CB-PDMS material is studied. Deflection of bimorph for change in temperature is studied for different thickness and volume percentage of CB bimorph. Three different thicknesses and three volume fractions of CB are used for analysis of bimorph. Deflections of the bimorph are obtained from two different approaches analytical and FE. The modelling of bimorph carried out using multi-physics (FE) software. Results obtained from above approaches are agreeing well with different volume fractions of CB and thickness. It is observed that the bimorph with higher amount of CB has larger deflection. An optimum deflection achieved in an equal layer of bimorph actuators. In this study, the largest displacement noticed at 6 mm thick CB-PDMS layer with 5 Vol% of carbon black filler.
Abstract: The microstructures of Co–GaSb junctions in samples annealed at 300, 400, 500, and 600°C in a N2 atmosphere were characterized using transmission electron microscopy (TEM) in combination with energy-dispersive spectrometry (EDS), nanobeam electron diffraction (NBD), and the selected area diffraction patterns (SADPs). The isolated CoSb3(Ga) phase started to form at the interface of Co/GaSb in the temperature of 400°C and then the CoSb3(Ga) phase changed to a continues layer at the interface when the annealing temperature was increased to 500°C. Upon increasing the temperature to 600°C, a large amount of Ga from GaSb diffused out toward Co to form a CoGa layer. The specific contact resistivity of Co/GaSb contact was evaluated by circular transmission line model (CTLM) and indicated that the lowest value was 5.410-4 Ω-cm at annealing temperature of 500°C and possessed high current density of 41.7 A/cm2 at 1V. These results indicate that the annealing temperature of the Co/GaSb structure could be maintained below 500°C for the successful formation of low-resistance metal Co/GaSb contacts in GaSb-based p-type metal-oxide-semiconductor field-effect transistors.
Abstract: The study is focused on the comparisons among three stochastic fatigue crack growth models through evaluations of experimental data. The first model assumed that the coefficient and exponent parameters of Paris-Erdogan law are mutually dependent normal random variables. The second model assumed that the fatigue crack growth rate equals to the deterministic Paris-Erdogan law multiplied by a stationary log-normal random factor while the third model proposed by the author was assumed that the fatigue crack growth rate equals to a deterministic polynomial in terms of fatigue crack size multiplied by a stationary log-normal random factor. Compact-tension specimens cut from a 2024-T351 aluminum-alloy plate were used for fatigue crack growth experiments under constant loads performed on thirty specimens. The normal probability paper for the first model was investigated to show the validity of the normal random parameter, and the log-normal probability papers for the second and third models were also investigated to show the validity of log-normal assumption of the random factors. The investigations on the probability of crack exceedance and distribution of random time of the three models were also made, and the comparisons of the results for all models were made as well.
Abstract: The low temperature DC electrical conductivity of laminated conductive polymer composites with different concentrations of carbon fibers as a filler has been investigated. The electrical behavior below 105 K for all concentrations could be explained in terms of 3D Mott’s model that is the hopping conductivity can be considered as the dominating charge transport mechanism. From this model, the hopping distance, the density of state at Fermi level, and the decay constant for this material were determined.
Abstract: This work presents a systematic study of the effects of current pulsation on soft magnetic properties and giant magnetoimpedance (GMI) of nickel-iron (NiFe) coatings electrodeposited on copper wires. The specimens were prepared by the electrodeposition technique with controlled bath compositions and varied applied current waveforms. The microstructural and chemical investigations indicate that current pulsation with 50% duty cycle and 50 Hz frequency provides significantly smoother coating surface of uniform nodules, with comparable Fe content but different phase composition, as compared to the direct current condition. The vibrating sample magnetometer evidently shows that the deposits prepared with a pulsed current exhibit relatively small coercivity, below 4 Oe. Using the four-point probe technique, the MI ratio of the pulse deposits is found to reach a significantly high value above 2,000% with decent sensitivity. The benefits of current pulsation in improving the characteristics of NiFe deposits, and correspondingly the alloys’ soft magnetic properties and MI effects are demonstrated.
Abstract: This study compared the ballistic performance of alumina (Al2O3)/ zirconia (ZrO2) functionally graded material (FGM) specimens with various levels of thickness and ZrO2 content and a pure Al2O3 single-layer ceramic composite (PCM). Ballistic tests were conducted with 0.3-inch armor-piercing (AP) projectiles, and finite element code LS-DYNA was used to examine energy absorption, stress distribution, and ceramic cone failure in the specimens. The findings are as follows: First, regarding energy absorption per unit of areal density, the 5% FGMs had the highest ballistic performance, which increased by up to 8%. By contrast, the ballistic performance of the 15% FGMs declined significantly to lower than that of the PCM. Second, the capability of the ceramic cone to withstand stress damage and projectiles was significantly greater in the 5% FGMs than in the 15% FGMs. Third, the wave impedance variations increased with the ZrO2 content in each layer, thereby enhancing the interactions between impact waves and aggravating ceramic damage. Thus, the intensities of transmission and reflection waves in the 15% FGMs increased, thereby causing reductions in its ballistic performance.
Abstract: We report the structural, bioactivity and antibacterial effect of silver nanoparticle embedded calcium borosilicate ceramics obtained by a simple sol-gel route and post annealing approach. The structural properties were studied by means of powder X-ray diffraction (XRD), UV-visible, Fourier transform infrared (FTIR) and transmission electron microscopy (TEM). The glass-ceramic nature of the sample was confirmed by XRD and FTIR. TEM and UV spectrum reveal the Ag nanoparticle embedment on amorphous matrix. The hydroxyapatite layer formation is investigated by in-vitro approach using Dulbecco’s Modified Eagle’s Medium. The antibacterial effects were tested with different bacteria using an agar well diffusion method. Samples show good antibacterial effect without compromising the formation of hydroxyapatite.