Stability of Y-Ti-O nanoparticles during laser deposition of oxide dispersion strengthened steel powder

This study investigated the feasibility of a direct energy deposition process for fabrication of oxide dispersion strengthened steel cladding. The effect of the laser working power and scan speed on the microstructural stability of oxide nanoparticles in the deposition layer was examined. Y-Ti-O type oxide nanoparticles with a mean diameter of 45 nm were successfully dispersed by the laser deposition process. The laser working power significantly affected nanoparticle size and number density. A high laser power with a low scan speed seriously induced particle coarsening and agglomeration. Compared with bulk oxide dispersion strengthened steel, the hardness of the laser deposition layer was much lower because of a relatively coarse particle and grain size. Formation mechanism of nanoparticles during laser deposition was discussed.     

Microstructure,Tensile and Fatigue Properties of Al–5 wt.%Mg Alloy Manufactured by Twin Roll Strip Casting

This study investigated the microstructure, tensile and fatigue properties of Al–5 wt.%Mg alloy manufactured by twin roll strip casting. Strips cast as a fabricated (F) specimen and a specimen heat treated (O) at 400 °C/5 h were produced and compared. In the F specimen, microstructural observation discovered clustered precipitates in the center area, while in the O specimen precipitates were relatively more evenly distributed. Al, Al₆(Mn, Fe), Mg₂Al₃ and Mg₂Si phases were observed. However, most of the Mg₂Al₃ phase in the heat-treated O specimen was dissolved. A room temperature tensile test measured yield strength of 177.7 MPa, ultimate tensile strength of 286.1 MPa and elongation of 11.1% in the F specimen and 167.7 MPa (YS), 301.5 MPa (UTS) and 24.6% (EL) in the O specimen. A high cycle fatigue test measured a fatigue limit of 145 MPa in the F specimen and 165 MPa in the O specimen, and the O specimen achieved greater fatigue properties in all fatigue stress conditions. The tensile and fatigue fracture surfaces of the above-mentioned specimens were observed, and this study attempted to investigate the tensile and fatigue deformation behavior of strip cast Al–5 wt.%Mg based on the findings.     

Mechanical property and fracture behavior of squeeze-cast Mg matrix composites

The present study aims to investigate the microstructure and fracture properties of AZ91 Mg matrix composites fabricated by the squeeze-casting technique, with variations in the reinforcement material and applied pressure. Microstructural and fractographic observations, along with in situ fracture tests, were conducted on three different Mg matrix composites to identify the microfracture process. Two of them are reinforced with two different short fibers and the other is a whisker-reinforced composite. From the in situ fracture observation of Kaowool-reinforced composites, the effect of the applied pressure on mechanical properties is explained using a competing mechanism: the detrimental effects of fiber breakage act to impair the beneficial effects of the grain refinement and improved densification as the applied pressure increases. On the other hand, for the composites reinforced with Saffil short fibers, microcracks were initiated mainly at the fiber/matrix interfaces at considerably higher stress intensity factor levels, while the degradation of fibers was not observed even in the case of the highest applied pressure. This finding indicates that the higher applied pressure yields better mechanical properties, attributable to the Saffil short fibers having relatively high resistance to cracking. Although an improved microstructure was obtained by accommodating the appropriate applied pressure in the short fiber-reinforced composites, their mechanical properties were far below those of conventional A1 matrix composites. In this regard, the Alborex aluminum borate whisker is suggested as a replacement for the short fibers used in the present investigation, to achieve better mechanical properties and fracture toughness.     

Microstructural study on effects of C-alloying on Cu-Fe-P cast alloy

The effects of C-alloying on the microstructure and secondary phase particles of Cu-2.5Fe-0.1P cast alloy were investigated by transmission electron microscopy (TEM), high-resolution electron microscopy (HREM), and image simulation. The mechanical and electrical properties were slightly improved, and grain refinement and fine γ-Fe particles were evident. Additionally, the Fe₃P particles were characterized, and abnormally grown Fe₃P particles were observed at the grain boundary in the non C-alloyed and C-alloyed specimens.     

Characterizations and electrochemical performance of pure and metal-doped Li4Ti5O12 for anode materials of lithium-ion batteries

Pure and metal (Cu, Al, Sn, and V)-doped Li₄Ti₅O₁₂ powders are prepared with solid-state reaction method. The effects of dopants on the physical and electrochemical properties are characterized by using TGA, XRD, and SEM. Compared with pure Li₄Ti₅O₁₂, metal-doped Li₄Ti₅O₁₂ powders show structural stability and enhanced lithium ion diffusivity brought by doped metal ions. Voltage characteristics and initial charge–discharge characteristics according to the C rates in pure and metal-doped Li₄Ti₅O₁₂ electrode materials are studied. Pure Li₄Ti₅O₁₂ powder shows a relatively good discharge capacity of 164 mAh/g at a rate 0.2C, and some of metal-doped Li₄Ti₅O₁₂ powders show higher discharge capacities. Metal-doped Li₄Ti₅O₁₂ powders are promising candidates as anode materials for lithium-ion batteries.     

Statistical description of the effect of Zr addition on the behavior of microcracks in Cu–6Ni–2Mn–2Sn–2Al Alloy

As possible substitutes for high-strength Cu–Be alloys, Cu–6Ni–2Mn–2Sn–2Al alloys have been developed. To clarify the physical background of the effect of trace Zr on the fatigue strength of such alloys, the initiation and propagation behavior of a major crack that led to the fracture of the tested specimens was monitored. When the stress amplitude was less than σ _a = 350 MPa, the fatigue life of the alloys with Zr was about 2–2.5 times larger than that of the alloy without Zr. When σ _a > 350 MPa, the effect of Zr addition on the fatigue life dramatically decreases as the stress amplitude increases. The increased fatigue life due to Zr addition resulted from an enhancement of the crack initiation life and microcrack growth life. The enhanced crack initiation life was mainly attributed to the strengthening of grain boundaries due to the precipitation of SnZr compounds. A statistical analysis of the behavior of multiple cracks was made to quantitatively evaluate the scatter in fatigue behavior. The statistical analysis supported the conclusions obtained from the behavior of a major crack.     

Photocatalytic performance of nanocrystalline Bi5Ti3FeO15 layered perovskite under visible light

Nanocrystalline Bi5Ti3FeO15 layered perovskite exhibiting Aurivillius phase was synthesized by polymerized complex (PC) method and investigated for its physico-chemical as well as optical properties. The crystallization of Bi5Ti3FeO15 synthesized by PC method was found to occur in the temperature range of 800-1050 degress C, whereas the single crystalline Bi5Ti3FeO15 formed at 1030 degrees C by solid state reaction (SSR) method. The observation of highly pure phase and such lower crystallization temperature in Bi5Ti3FeO15 prepared by PC method, is in total contrast to that observed in Bi5Ti3FeO15 prepared by the conventional solid-state reaction (SSR) method. The band gap of nanocrystalline Bi5Ti3FeO15 determined from UV-Vis diffusion reflectance spectrometer was 2.38 eV (525 nm). The photocatalytic activity of Pt/Bi5Ti3FeO15 prepared by PC method was investigated with the photodecomposition of isopropyl alcohol (IPA) and hydrogen production from water-methanol mixed solution under visible light (lambda > or = 420 nm). The respective activities for PC sample were higher than that of Pt/Bi5Ti3FeO15 prepared by SSR as well as Pt/TiO(2-x)N(x).     

The effect of microstructural inhomogeneity on the growth paths of surface-cracks in copper processed by equal channel angular pressing

The growth behavior of cracks is monitored on specimens of ultrafine grained copper produced by equal channel angular pressing. Temporary retardation of crack growth under low stress amplitudes occurs when the crack length reaches about 0.1 mm, but there is no similar retardation at high stress amplitudes. Dependent on stress amplitude, different crack growth path morphologies develop. Analysis of the fracture surfaces is conducted by scanning electron microscopy, showing planer, granular and striated surfaces. The physical background of growth path and fracture surface formation is discussed by considering crack growth mechanism and microstructural inhomogeneity.     

Potential biomass supply for agro-pellet production from agricultural crop residue in Nepal

Nepal, a country rich in biomass, still does not have any commercial pellet production plants and is wasting large amounts of agricultural crop residue. The current study showed that about 5.61 million tonnes (Mt) of biomass in the form of pellets are potentially available from agricultural crop residues. The brick and cement industries could use these agro-pellets. Co-firing of pellets in such industries could play an important role in reducing the import volume of coal and minimize the related environmental loadings.