Effects of Bi content on thermal,microstructure and mechanical properties of Sn-Bi-In-Zn solder alloy systems

Journal of Materials Science: Materials in Electronics - In the present study, various amounts of Bi were added to two groups of Sn-In-Zn lead-free solder alloy systems (Sn-[x] Bi-2In-9Zn...     

Experimental determination of thermal conductivity of solid and liquid phases in Bi−Sn and Zn−Mg binary eutectic alloys

The thermal conductivities of solid phases, K_s, for Bi-43 wt.% Sn and Zn-0.15 wt.%Mg binary alloys at their eutectic temperature are found to be 28.0 τ 1.4 and 137.4–6.9 W/Km, respectively, with a radial heat flow apparatus. The thermal conductivity ratios, R, of liquid phase to solid phase for the same alloys at their eutectic temperature are found to be 0.93 and 0.78, respectively, with a Bridgman type directional solidification apparatus. Thus, the thermal conductivities of the liquid phases, K_L, for Bi-43 wt.%Sn and Zn-0.15 wt.%Mg binary alloys at their eutectic temperature are evaluated to be 26.0−1.3 and 107.2−5.4 W/Km, respectively, from the measured values of K_s and R.     

Experimental determination of interfacial energy for solid Zn solution in the Sn-Zn eutectic system

The grain boundary groove shapes for Zn solid solution in equilibrium with Sn-Zn eutectic liquid were observed with a radial heat flow apparatus. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient, the solid-liquid and the grain boundary energy for the Zn solid solution in equilibrium with Sn-Zn eutectic liquid were determined to be (2.32 ± 0.13)×10⁻⁸ Km, (120.87 ± 13.29)×10⁻³ J.m⁻² and (194.76 ± 23.37)×10⁻³ J.m⁻², respectively. The termal conductivity of the eutectic Sn-9 wt% Zn solid solution, κ _S , was obtained as 74.74 W/Km by using a radial heat flow apparatus. The thermal conductivity ratio of the eutectic liquid to the eutectic solid, R = κ _L /κ _S was found to be 0.58 with a Bridgman-type directional growth apparatus. Thus, the value of the thermal conductivity of eutectic Sn-9 wt% Zn liquid solution, κ _L , was obtained as 43.82 W/Km.     

The measurement of interfacial energies for solid Sn solution in equilibrium with the Sn–Bi–Ag liquid

The equilibrated grain boundary groove shapes of solid Sn solution in equilibrium with Sn–Bi–Ag liquid were observed from a quenched sample by using a radial heat flow apparatus. The Gibbs–Thomson coefficient, solid–liquid interfacial energy, and grain boundary energy of the solid Sn solution were determined from the observed grain boundary groove shapes. The thermal conductivity of the solid phase for Sn-10 at.%Bi-2 at.%Ag alloy and the thermal conductivity ratio of the liquid phase to the solid phase for Sn-10 at.%Bi-2 at.%Ag alloy at the melting temperature were also measured with a radial heat flow apparatus and a Bridgman-type growth apparatus, respectively. A comparison of present results for solid Sn solution in the Sn–10 at.%Bi–2 at.%Ag alloy with the results obtained in previous works for similar solid Sn in equilibrium with different binary or ternary liquid was made. From the comparison, it can be concluded that for solid Sn solution in equilibrium with different liquid, the Gibbs–Thomson coefficient seems to be constant and does not depend on the composition of liquid but solid–liquid interfacial energy changes little bit with composition of liquid at a constant temperature.     

Increased fuel burn up in a CANDU thorium reactor using weapon grade plutonium

Weapon grade plutonium is used as a booster fissile fuel material in the form of mixed ThO₂/PuO₂ fuel in a Canada Deuterium Uranium (CANDU) fuel bundle in order to assure the initial criticality at startup.Two different fuel compositions have been used: (1) 97% thoria (ThO₂) + 3%PuO₂ and (2) 92% ThO₂ + 5% UO₂ + 3% PuO₂. The latter is used to denaturize the new ²³³U fuel with ²³⁸U. The temporal variation of the criticality k_∞ and the burn-up values of the reactor have been calculated by full power operation for a period of 20 years. The criticality starts by k_∞ = 1.48 for both fuel compositions. A sharp decrease of the criticality has been observed in the first year as a consequence of rapid plutonium burnout. The criticality becomes quasi constant after the second year and remains above k_∞ > 1.06 for 20 years. After the second year, the CANDU reactor begins to operate practically as a thorium burner.Very high burn up could be achieved with the same fuel material (up to 500,000 MW·D/T), provided that the fuel rod claddings would be replaced periodically (after every 50,000 or 100,000 MW·D/T). The reactor criticality will be sufficient until a great fraction of the thorium fuel is burnt up. This would reduce fuel fabrication costs and nuclear waste mass for final disposal per unit energy drastically.     

Numerical simulation of the thermal history multiple laser deposited layers

Multilayer direct laser metal deposition is a fabrication process in which the parts are fabricated by creating a molten pool into which metal powder particles are injected, and a layer is laid down by moving the pool. Height is added by creating additional layers on top of the first layer. During fabrication, a complex thermal history is experienced in different regions of the build. The thermal history includes the reheating process for previously deposited layers caused by subsequently deposited layers. The objective of this study is to provide insight into the thermal history during the direct laser deposition process. Using the commercial ABAQUS/CAE software, a thermomechanical 3D finite element model was developed. This work presents a 3D heat transfer model that considers the continuous addition of powder particles in the front of a moving laser beam using ABAQUS/CAE software. The model assumes the deposit geometry appropriate to each experimental condition and calculates temperature distribution, cooling rates, and remelted layer depth which can affect the final microstructure. Model simulations were qualitatively compared with experiments results acquired in situ using a K-type thermocouple.     

The Measurement of Thermal Conductivity Variation with Temperature for Sn-Based Lead-Free Binary Solders

The variations of thermal conductivity with temperature in the Sn-based lead-free binary solders, Sn-10 wt pct X (X = Ag, In, Bi, Cu, Sb, Zn), were measured by using the linear heat flow apparatus. The thermal conductivities of Sn-based lead-free solders at their melting temperature were obtained from graphs of thermal conductivity variation with temperature. The variations of electrical conductivity with temperature for same solders were also determined from the Wiedemann–Franz (W–F) equation by using the measured values of thermal conductivity.