Defect and Diffusion Forum Vols. 312-315

Abstract: Diffusion couple experiments were performed in the Co-Ni binary system for determining inter-, impurity- and intrinsic-diffusion coefficients in the temperature range of 1050 - 1250°C. The activation energy and pre-exponential factor estimated for interdiffusion do not vary significantly with composition. The activation energy calculated for impurity diffusion experiments shows is higher than . Intrinsic diffusion coefficients estimated from the multifoil experiment show that Ni is the fastest diffusing species in this system.

Abstract: The microstructure and hydrogenation property of hyper-eutectic Mg-Ni alloys were investigated. The specimens were Mg-31 mass%Ni, Mg-41 mass%Ni and Mg-50 mass%Ni alloys that are composed of primary Mg2Ni crystal and Mg-Mg2Ni eutectic structure. The amount of the primary Mg2Ni phase increased as the content of Ni increased. The hydrogenation behavior strongly depended on the Ni content and the number of the hydrogenation cycle, that is, as the increase of the Ni content in the specimen, the hydrogen absorption rate increased while the hydrogen absorption weight decreased. At the first cycle measurement, hydrogen absorption was slow for the Mg-31 mass%Ni alloy while hydrogen was rapidly absorbed for the Mg-50 mass%Ni alloy at 300°C. In all the specimens, saturation of the hydrogen absorption was achieved within a few minutes after the second cycle measurement. The maximum values of the hydrogen absorption weight decreased from 5.5 mass% to 4.1 mass% as the Ni content increased.

Abstract: The enhancement of impingement heat transfer on a flat plate covered with a thick layer of porous medium with or without a center hole was numerically investigated. The renormalization group turbulence model is selected for the fluid region while Forchheimer extended Darcy’s model is used for porous region. The numerical models were justified by comparisons with available experimental data. Computational results show that an attached porous medium with a center hole can effectively enhance jet impingement heat transfer while an attached thick porous layer without a center hole has detrimental effect. The physics of these results are supported and well explained by the detailed flow patterns. The most influential parameters in this heat transfer process include the jet Reynolds number and the center hole geometry (hole depth and jet-to-hole diameter ratio). A good hole geometry should well trap the jet and direct the coolant along the heated plate.

Abstract: In the present study, the isothermal early oxidation behaviour of the WE54 and Elektron 21 alloys were studied at a temperature of 773 K in pure O2 up to 150 min. The results showed that the oxidation kinetics depending on the chemical composition and microstructure of the investigated alloys. The oxidation kinetics of these alloys in as-cast and T6 conditions obtained a parabolic law, while in supersaturated state these alloys exhibited a linear kinetics. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses indicated that an oxide film, composed of MgO and (Y,Dy)2O3 in WE54 alloy and (Nd,Gd)2O3 in Elektron 21 alloy, had been formed.

Abstract: In the present study, the thermal diffusivity and conductivity of WE54 and Elektron 21 alloys were studied. The results showed the thermal diffusivity of WE54 and Elektron 21 alloys were temperature and microstructure dependent. The thermal diffusivity of both alloys was dependent on the content of the solute element in the α-Mg matrix. The solid solution of Y and Gd in Mg has a lower thermal conductivity than alloys where the intermetallic Mg3(Nd,Gd) and Mg14Y2Nd phases are present. The formation of strengthening phases during ageing caused the consumption of the solute element in the α -Mg matrix, and improved the thermal conductivity of the alloys.

Abstract: Solute transport in porous media concerns advection, dispersion, sorption, and reaction. Since porous media is commonly heterogeneous, the properties of porous media are spatially and temporally variable. In this paper, one dimensional unsteady solute transport in semi-infinite heterogeneous porous media is investigated. Both linear and nonlinear decay is considered. Analytical solution is obtained for linear decay with spatially and temporally diffusion coefficient and velocity by using generalized integral transform technique. The inverse integral transforms are developed for the problems in semi-infinite space based on some weighted functions. Some examples are given to show the application of the method and analytical solutions.

Abstract: In this study, friction stir processing (FSP) was applied to fabricate a Cu/SiC surface composite layer by incorporation of 5 µm SiC particles. Effects of the traverse speed and SiC volume fraction on the microstructure, hardness and powder distribution pattern of the developed surface layer were investigated. Optical and scanning electron microscopy (SEM) was employed to carry out the microstructural observations. Results show that increasing the volume fraction causes an intense decrease in the grain size and increase in the hardness of the developed surface. To achieve a uniform distribution of particles and uniform microstructure, the traverse speed should decrease as far as possible.

Abstract: The hydrogen solubility and the hydrogen permeability have been measured for Nb-based alloys in order to investigate the alloying effects on the hydrogen diffusivity during hydrogen permeation. It is found that the hydrogen solubility decreases by the addition of ruthenium, tungsten or molybdenum into niobium. The mobility for hydrogen diffusion during hydrogen permeation is estimated from the linear relationship between the normalized hydrogen flux, , and the product of the hydrogen concentration and the difference of hydrogen chemical potential, . It is found that the mobility for hydrogen diffusion during hydrogen permeation is larger for Nb-based alloys than pure niobium, especially at low temperature. The activation energy of the mobility for hydrogen diffusion decreases by the addition of ruthenium, tungsten or molybdenum into niobium.

Abstract: Hydrophilic membranes based on PVP, containing 0.4 and 1% of carboxymethylcellulose staple fibers infused with calcium alginate were obtained and characterized in this study. The main proposal of this study is related to hydrogels based on PVP modified with carboxymethyl cellulose staple fibers infused with calcium alginate. This modified hydrogel is a hydrophilic membrane with better mechanical properties that can incorporate adequate drugs into the fibers for each lesion type. The hydrogels were obtained using ionizing radiation with an electron beam, at a dose of 25 kGy. The membrane’s characterization was performed by tensile and physic-chemical tests (gel fraction and swelling). The results obtained showed that the membranes have higher mechanical strength, a higher swelling degree and a lower gel fraction.

Abstract: Soldering processes involving the use of Pb have been known and practiced for more than 5000 years. In 2000, the European Union imposed a ban on the use of Pb because of the fact that Pb is poisonous to humans. Consequently, attempts are being made worldwide to develop a Pb-free solder. Among the various Pb-free solders, the Sn–0.75wt%Cu (Sn-0.75Cu) solder is the suitable one from the viewpoint of cost. Moreover, its acoustic properties are superior to those of the other Pb-free solders. However, the Sn-0.75Cu solder has a few disadvantages: its joining strength is lower than that of the other solders, and its melting temperature is higher than that of the Sn-37wt%Pb (Sn–Pb) solder. Therefore, we have attempted to decrease the melting temperature and improve the joining strength of Sn-0.75Cu to match those of the Sn–Pb solder. It is well known that when Ga is added to a Sn-based alloy, the melting temperature of the alloy decreases. Moreover, Ga has superior wettability. Therefore, we added Ga to the Sn-0.75Cu solder in order to improve the joining strength and decrease the melting temperature of the solder. We observed that the melting temperature of Sn95.3Cu0.7Ga4 reduced to less than that of the Sn–Pb solder. We also investigated the joining strength between the Ga-added solder and a Cu wire. We observed that the joining strength increased with an increase in Ga content, was the highest for Sn97.3Cu0.7Ga2, and then decreased with an increase in Ga content. The peak joining strength of the Ga-added solder was almost 1.5 times that of the Sn-0.75Cu solder. However, the brittleness of the solder increased with an increase in the Ga content. This is a disadvantage of the addition of Ga to Sn.