Advanced Materials Research Vol. 509

Abstract: LiFePO₄ has been considered as the most promising positive electrode due to its low cost, high theoretical capacity, stability and low toxicity, all highly required in vehicle applications. In this work, LiFePO₄ compound was synthesized by the solid carbothermic reduction reactions with different Li resource. The pure LiFePO4 phase was confirmed for all samples by analysis of the XRD results. The different morphologies were obtained due to different Li resources. The potential plateau of all samples is in the range from 3V to 4V. The sample (LiCO₃ as the Li resource) has a higher discharge capacity of 118mAhg⁻¹ at 0.2C 20% greater than that of the sample (LiOH as the Li resource). The reason comes maybe from nano pore characteristics, which reduce Li ion diffusion distance, and increase the utilization efficiency of material.

Abstract: The pulse current was performed on the IN718 alloy during tensile test at room temperature and elevated temperature in the present study. The effect of pulse current on the deformation behavior of the alloy and the mechanisms were investigated. The results show that the deformation resistance decreases and the elongation increases significantly of IN718 alloy during tensile test at room temperature and 1073 K with the increase of pulse current. And the effect of pulse current on the strength and plasticity of the alloy increases as pulse current energy increases. The electroplastic effect of pulse current can promote the dislocation motion, and thus decrease the deformation resistance of the alloy during the tensile deformation. The pulse current reduces the starting temperature of recrystallization, promotes the recrystalllization nucleation, and thus makes it possible that the dynamic recrystallization would occur at lower temperature than that in the conventional temperature field. This is the main reason for the decrease of deformation resistance and the increase of plastic deformation ability of IN718 alloy under pulse current.

Abstract: Rare earth (RE) has purification, denatured mixture and micro alloy function in steel. High Nb containing in steel can expend austenite non-recrystallization region, improve rolling temperature and lower equipment load. Effect of RE on dynamic recrystallization of low carbon high niobium steel is investigated by using thermal simulation experiment in this paper. Experimental results show that dynamic recrystallization does not occur in two test steel below 1000°C. RE elements can increase dynamic recovery beginning strains, refine and disperse M/A organization and change precipitates into small triangle shape.

Abstract: In present work, the Mg−Gd−Nd−Y−Zn alloy sheets were prepared by hot extrusion technique. The microstructure, texture and mechanical properties of the extruded alloy were investigated. After hot extrusion, the alloy reveals a greatly refined microstructure due to the dynamic recrystallization. The coarse eutectic phases were crushed into small particles during extrusion process, which brings a promotion of grain refinement. A weak basal fiber texture was obtained in the as-extruded alloy owing to the influence of RE (rare earth) alloying elements. The as-extruded alloy exhibits mechanical anisotropy that the strengths and elongations in the extrusion direction are both higher than those in the transverse direction. And this behavior does not change with increasing temperature. It results from the weak texture and the distribution of eutectic phase particles in the alloy sheet. Through isothermal aging treatment, significant strengthening is achieved in the peak-aged alloy, and the mechanical anisotropy still exists.

Abstract: The property and microstructure of rolled non-quenched and tempered steels of Nb-V comprehensive micro alloying have been investigated .The mechanical properties and the load –displacement curves were measured respectively by using electron tension test machine and digital-impact test machine . The microstructure and fracture surface of impact samples were observed with SEM .The results show that micro-alloying Nb and V non-quenched and tempered steel behaves higher tension strength and toughness than that of only V micro-alloying one under the condition of about same plasticity. Improvement of the properties is related with that Nb can effectively make fine pearlite group and inter-lamella spacing at the impact fracture pearlite flakes. Corresponding relationship between various domain of fracture morphology and characteristics points at the curve of digital impact has been discussed.

Abstract: Energy consumption of buildings has exceeded 25% of total social energy consumption and new techniques and new materials are greatly demanded in buildings in order to save the energy. As an important clean renewable energy resource, solar energy is expected to be used in buildings instead of traditional energy including petroleum and coal. Phase change material (PCM) can absorb solar energy, transfer it to heat, and store it through phase change process. When needed, the energy absorbed can be released. By this way, the room temperature in a building can be maintained in a comfortable region without input of extra energy. Therefore, PCM is a promising material for energy saving and will be widely used in various applications as well as buildings. In this paper, three kinds of encapsulated phase change materials, i.e., shape-stabilized PCM (FSPCM), absorbed PCM and PCM microcapsule are introduced. Their preparation methods and physical properties as well as typical applications are compared.

Abstract: Nickel-oxide duplex coatings were successfully deposited on magnesium alloy (AZ91D) by anodizing and electroless nickel-phosphorus plating processes. The anodizing interlayer was used to increase the adhesion strength of Ni-P layer. The electroless Ni-P coating enhances the corrosion resistance of the anodic oxide layer. Specimen of AZ91D magnesium alloy was polished firstly. The anodizing process was preceded in alkaline anodizing solution at 24 °C, and the bath voltage maintained at 70 volts for 2 hours. Successive electroless Ni-P plating was used to achieve the sandwich structure. The surface morphologies of the coatings were observed by field-emission scanning electron microscopy (FE-SEM). The adhesion strength was measured by pull-off tester. The electrochemical behavior of coatings with corrosion resistance in 3.5 wt.% NaCl solution was evaluated by potential polarization curve. The experimental results showed that the adhesion strength of directly deposited coating and duplex coating were 115.4 kg_f/cm² and 142.2 kg_f/cm², respectively. The adhesion strength of coatings on AZ91D magnesium alloy was improved by the synergistic effect between anodized magnesium oxide and Ni-P layer in duplex coating.

Abstract: The influence of Sn content on the microstructure and mechanical properties of Ti-35Nb-XSn (X=0, 3, 6, 9) alloy was investigated in this paper. It is shown that Ti35Nb alloy is composed of β, α and α” phases after solution treatment at 800°C. The α" and α phases disappear and single β phase is obtained with the addition of Sn element. The strength of the alloys increases and the elongation decreases with increasing Sn content. Meanwhile, it is found the addition of Sn element makes the elastic moduli of the alloys much lower than that of Ti35Nb alloy.

Abstract: The local mechanical properties and microstructures in a real dissimilar metal welded joint (DMWJ) of nuclear power plant were investigated. Results show that the distributions of mechanical properties in the DMWJ are very inhomogeneous. Especially in the three interface regions of A508/Alloy52Mb, Alloy52Mb/Alloy52Mw and Alloy52Mw/316L, the inhomogeneous characteristics are most prominent, and some local softening and hardening zones are formed. This non-uniform distribution on mechanical properties is mainly caused by the different microstructures in the DMWJ. The local dramatic variations in mechanical properties and local mismatch effect in the softening and hardening zones have significant effects on macroscopic fracture mechanics parameter, local crack initiation and growth behavior. But they are not considered in present structure integrity assessment codes and Leak-Before-Break (LBB) analysis. For assessing integrity and conducting LBB analysis on the DMWJ accurately, it is necessary to determine the local mechanical properties and their local mismatch ratios. In addition, the new integrity assessment and LBB analysis methods based on local damage and fracture need to be developed.

Abstract: Two oxides, Y₂O₃ and Nb₂O₅, were doped into Bi₂O₃-based electrolyte in a composition of (Bi _1-x-y,Nb _x,Y _y)₂O ₃, where (x+y)=0.12 to 0.2 and the x:y ratio 3:1 to 1:3. The delta-phase retention, the oxygen vacancy order-disorder transformation, the ionic and electric conductivity were investigated by various techniques. The long-term conductivity of the dense electrolytes was determined showing moderate degradation due to phase transformation possible triggered by surface evaporation of Bi-oxide. The best retention of the conductivity is about 60% after 300 hr test.