Papers by Keyword: Interfacial Structure

Abstract: The application of hybrid structures or components made of dissimilar metal offers the potential to utilize the advantages of different materials often providing unique solutions to engineering requirements. However, the joining of materials by conventional welding techniques becomes difficult if the physical properties such as melting temperature and thermal expansion coefficients of the two materials are different. In this study, a new process of joining semi-solid AISI D2 tool steel and AISI 304 stainless steel using a partial remelting method is proposed. Moreover, the effect of the holding time on the microstructural evolution was investigated. The processing temperatures for the thixojoining was 1320°C and held for 5, 12, 20 and 30 minutes, respectively. The results obtained from investigating the basic geometries demonstrated a good joining quality that differs from the conventional process of welding. Metallographic analyses along the joint interface between semi-solid AISI D2 and 304 stainless steel showed a smooth transition from one to the other, with neither oxides nor microcracking being observed.

Abstract: The 7075/6061 bimetallic composite ingots were prepared by semi-solid/liquid method. The microstructure characteristics of composite ingots were studied, and the diffusion law of interface components was analyzed. The results show that the semi-solid/liquid composite of 7075 and 6061 can be realized under the conditions of casting temperature of 983 K, semi-solid heating temperature of 918 K, holding time of 1h, and rapid water cooling. The obtained composite ingot has a layered distribution characteristic of "semi-solid microstructure/dendritic structure". The interface is clear, continuous, and free of impurities. From the interface to the semi-solid side, it shows such a pattern of change: “Dendritic structure” →”Semidendritic and hemispherical” → “Globularization”. Through the observation of the microstructure and the analysis of the components, the semi-solid/liquid composite mechanism is discovered to be a combination of fusion bonding and diffusion bonding.

Abstract: The magnesium hydroxide (MH) whiskers / ABS composites were prepared by melt-extrusion with modified whiskers as filler. The mechanical performances, including the tensile strength, elongation at break and elastic modulus, were tested by electronic universal testing machine. The results showed that with the increasing of the whisker dosage, the tensile strength and elongation at break reduced gradually, and the elastic modulus get maximum when it is 25%.The morphology on fracture of composites was analyzed by SEM. The conclusions are the whiskers of surface modifications can be evenly distributed in the composites and bond partly with ABS. that it is necessary to enhance the combine strength of interface on excellence performances of composites.

Abstract: Composites have achieved much attention because of their excellent qualities. Core-shell γ-Fe₂O₃/Au nanoparticles were prepared by chemical reduction. Their optical properties and morphology were characterized by UV-visible spectrum (UV-vis), X-ray diffraction (XRD) and Transmission Electronic Microscopy (TEM). Furthermore, the average particle size and interface structure were also analyzed using small angle X-ray scattering (SAXS).

Abstract: The preference of the habit planes (HPs) developed from precipitation in the fcc/bcc system has been investigated. The interfacial energy of different interface orientations has been examined with variation of the orientation relationships (OR) and lattice parameters by a classical molecular dynamics method. The results show that interface has the lowest interfacial energy when it contains parallel Burgers vectors and a set of dislocations. The local minimum of interfacial energy may not associated with a maximum of dislocation spacing. It is also found that the near Kurdjumov-Sachs OR is more preferable than the near Nishiyama-Wasserman OR. Contrary to the previous interfacial energy calculations, which usually limit to rational ORs, the present work allows ORs to be irrational, which agrees with the observations.

Abstract: The slug flow regime may be appeared in subsea gas-liquid pipeline of the offshore petroleum industry. The gas entrainment process and the gas bubble distribution in liquid slug are crucial for the model of slug flow. An experimental facility was constructed and the gas bubble distributions in the liquid slug were measured by the dual-tip conductivity probe. It is found that the entrained gas is broken up into small bubbles by the high turbulent shear stress in the turbulent shear layer in the mixing zone. The small bubbles are dispersed completely and the profiles of void fraction and bubble frequency have peaks in this layer. The mechanism of gas entrainment is also presented.

Abstract: The magnesium oxysulfate whiskers/PE composites were prepared by melt-extrusion using whiskers as filler. The mechanical performances, including the tensile strength, elongation at break and elastic modulus, were tested by electronic universal testing machine. The results show that as the content of whiskers increases, the modulus of elasticity increases while the elongation decreases. However, the elastic modulus will improve and the tensile strength will be maximized when it is 15%. Hydrogen bond was formed between whisker and modifier after modification and was characterized by IR. The morphology of fracture was analyzed by SEM. It draws the conclusion that hydrogen bond is capable to enhance the mechanical performances of composites.

Abstract: Authors ultrasonically welded A6061 aluminum alloy sheet using two types of weld tips with the different contact face geometry, and investigated the effect of the weld tip geometry on the performance and the interface structure of welds. One type of tip has a cylindrical contact face without knurl, which is called C-tip in this study. The other type of tip has flat contact face with knurl, which is called K-tip in this study. The strength of the joints welded using C-tip was higher than that welded using K-tip and the C-tip could stably produce the higher strength joint.

Abstract: High-purity plates of Cu and Sn were diffusion bonded to clarify the early stage of the solid state interfacial reaction between Cu and Sn, focusing on the incubation time for the formation of intermetallic compounds. A clear incubation time for the formation of intermetallic compounds is observed at every temperature between 423 and 493 K. The incubation time changes depending on the annealing temperature. The interface annealed at 423 K for 3.60 ks maintains the direct interconnection between Cu and Sn being free of intermetallic compounds. The exposure of Cu surface to air affects the interfacial reaction. Annealing of the Cu/Sn interface at 493 K for 3600 s starts to form voids by using the Cu plates exposed for 8.64×104 s or longer to air. Furthermore, the reaction product layer formed by the same annealing condition becomes thinner when the Cu plates exposed for 8.64×105 s or longer to air are used.

Abstract: Two-dimensional in-plane interface structures of highly epitaxial perovskite (La,Ca)MnO3 (LCMO) and (Pb,Sr)TiO3 (PSTO) thin films on salt-rock type MgO substrate were studied using Transmission Electron Microscopy (TEM). Cross-section TEM studies revealed that both LCMO and PSTO films are good single crystal quality and have atomic sharp interface with respect to the MgO substrate with -6.4% and -6.2% lattice mismatch, respectively. Electron Diffraction Patterns (EDPs) of plan-view LCMO/MgO and PSTO/MgO interfaces exhibit double diffraction spots. An analytical approach was employed using double diffraction to study the two-dimensional in-plane interfaces of perovskite structure films on the salt-rock type substrate. The lattice mismatch near the interface regions was determined using EDPs of the plan-view interfaces and found to be -8.0% for LCMO/MgO and -7.14% for PSTO. Both latter values are larger than those obtained using cross-section TEM. Studies of the sharpness of double diffraction spots and plan-view high resolution (HR) TEM brought a conclusion that the PSTO film is well commensurate with the MgO substrate over large areas, whereas LCMO film is only locally commensurate with the substrate. These studies provide additional evidence to our previous observations that plan-view TEM of the interface is able to provide critical and valuable information that is lacking from the cross-section TEM analysis.