Creep Behavior and Microstructural Evolution of Al–Cu–Mg–Ag Alloys with Various High Cu Contents

The creep behavior and microstructural evolution of three Al–Cu–Mg–Ag alloys with Cu content around its solid solubility limit in Al (5.65 wt %) were investigated at 180–240 °C and applied stress of 150–300 MPa. The creep resistance of aged alloy, which is mainly determined by the number density of Ω phase, is the best for 6.00 wt % Cu, better for 5.30 wt % Cu, and the worst for 5.65 wt % Cu. After solid-solution treatment, the lowest Cu content in the Al matrix for the alloy with 5.65 wt % Cu is observed due to the existence of more residual phases. It results in the lowest number density of Ω phase the following aging and poor creep resistance. Increasing temperature from 180 to 240 °C at the same stress (225 MPa), the steady creep rate of alloys increases by 225 times, which is apparently larger than that (26 times) for increasing stress from 225 to 300 MPa at the same temperature (180 °C). It indicates that the coarsening of the Ω phase with increasing temperature should be more serious than that with increasing stress. The creep mechanism of Al–Cu–Mg–Ag alloy can be attributed to the dislocation climb with the existence of threshold stress.

Suitability of Sm3+-Substituted SrTiO3 as Anode Materials for Solid Oxide Fuel Cells: A Correlation between Structural and Electrical Properties

Perovskite anodes, nowadays, are used in any solid oxide fuel cell (SOFC) instead of conventional nickel/yttria-stabilized zirconia (Ni/YSZ) anodes due to their better redox and electrochemical stability. A few compositions of samarium-substituted strontium titanate perovskite, SmxSr1−xTiO3−δ (x = 0.00, 0.05, 0.10, 0.15, and 0.20), were synthesized via the citrate-nitrate auto-combustion route. The XRD patterns of these compositions confirm that the solid solubility limit of Sm in SrTiO3 is x < 0.15. The X-ray Rietveld refinement for all samples indicated the perovskite cubic structure with a P m 3 ¯ m space group at room temperature. The EDX mapping of the field emission scanning electron microscope (FESEM) micrographs of all compositions depicted a lower oxygen content in the specimens respect to the nominal value. This lower oxygen content in the samples were also confirmed via XPS study. The grain sizes of SmxSr1−xTiO3 samples were found to increase up to x = 0.10 and it decreases for the composition with x > 0.10. The AC conductivity spectra were fitted by Jonscher’s power law in the temperature range of 500–700 °C and scaled with the help of the Ghosh and Summerfield scaling model taking νH and σdc T as the scaling parameters. The scaling behaviour of the samples showed that the conduction mechanism depends on temperature at higher frequencies. Further, a study of the conduction mechanism unveiled that small polaron hopping occurred with the formation of electrons. The electrical conductivity, in the H2 atmosphere, of the Sm0.10Sr0.90TiO3 sample was found to be 2.7 × 10−1 S∙cm−1 at 650 °C, which is the highest among the other compositions. Hence, the composition Sm0.10Sr0.90TiO3 can be considered as a promising material for the application as the anode in SOFCs.

Germanium Incorporation in Silicon Carbide Epitaxial Layers Using Molecular Beam Epitaxy on 4H-SiC Substrates

Ternary (Si1-xCy)Gex+y solid solutions were grown on Si-face 4H-SiC applying atomic layer molecular beam epitaxy at low temperatures. The grown layers consist of twinned 3C-SiC revealed by cross section electron microscopy. The germanium was incorporated on silicon lattice sites as revealed by atomic location by channeling enhanced microanalysis transmission electron microscopy studies. The Ge concentration of the grown 3C-(Si1-xCy)Gex+y heteroepitaxial layers decreases with increasing growth temperatures, but exceeds the solid solubility limit.

Effects of Mechanical Alloying on Solid Solubility

Mechanical alloying (MA) is a potential processing method for various equilibrium and non-equilibrium alloy phases such as supersaturated solid solution, metastable crystalline, amorphous, quasi-crystalline phases, nanostructures. Compared to conventional high temperature material processing such as melting and casting, improvement of solid solubility limit results from mechanical alloying at room temperature. The solid solubility increases with increase in milling time due to enhanced stress assisted atomic diffusion during particle refinement and reaches a saturation level at higher milling time. The extension of solid solubility is attributed to thermodynamic, dynamic or kinetic factors such as high dislocation density due to severe plastic deformation during particle refinement and enhanced diffusivity during MA. The review aims to discuss the insight of MA than other non-equilibrium processing in terms of achieving higher solubility, reasoning and mechanism of solubility improvement during MA of different alloy systems.

Influence of Filler Rod Composition on the Strength of Tungsten Inert Gas Welded Magnesium Alloy Joint

The influence of filler rod composition on the strength of Tungsten Inert Gas (TIG) welded magnesium alloy joint was investigated. Samples were rolled AZ31 (Mg-3Al-1Zn) magnesium alloy as base metal and drawn AZ31, AZ61 and AZ91 magnesium alloys as filler rod. The results show that all fracture points were fusion zone (FZ), and each joint efficiency (=joint strength/ base metal strength) was 70.7%, 80.0% and 73.1% when using AZ31, AZ61 and AZ91 filler rod. When using AZ91 filler rod, 0.2% proof stress was the highest but the elongation was the lowest among the three conditions, and joint efficiency was lower than that when using AZ61 filler rod. It is thought that welded joint was strengthened by solute strengthening, but excess addition of aluminum facilitated crystallization of Mg17Al12 phase. This is the reason why elongation and joint efficiency when using AZ91 filler rod decreased. In conclusion, it is effective to use filler rod which does not excess solid solubility limit.