No description available.

No description available.

The influence on the as-cast grain size of a range of alloying additions to some TiAI-based alloys has been assessed using optical microscopy, analytical scanning and analytical transmission electron microscopy. It has been found that additions of boron, either as TiB2 or AlB 12,resulted in significant grain refinement, but of the other additives (yttrium, yttria, silicon and sulphur) only sulphur had any significant effect. Measurements of tensile properties of the grain refined alloys showed a significant improvement, and creep rates were not degraded. Failure of the fully lamellar structure during tests was found to occur by the splitting of grains, in the hard orientation, parallel to the lamellae. Determination of the nature of B-containing precipitates in the alloys, formed at high cooling rates, showed that they were a eutectic structure of either TiB and B2 or TiB2 and B2 depending upon alloy composition. At lower cooling rates TiB2 usually formed, unless Ta was present in the alloy in which case a complex structure of TiB and TaB formed. In all cases, irrespective of the alloy or boron addition method, a minimum concentration of about 0.6 at.% B was required to achieve an equiaxed grain structure in plasma-melted ingots. At lower concentrations the dendrite arm spacing and columnar grain width are reduced. In Ta and W-containing alloys there is a marked tendency for the borides to form large (400J.1m) clusters. The size and frequency of these clusters can be influenced by the sequence and the form in which the various alloying additions are made. The mechanism by which grain refinement occurs is the rejection of boron from the liquid during solidification, leading to local high concentrations of boron at the roots of the secondary dendrite arms, which under normal casting conditions then break off and act as nuclei for equiaxed grains. The boron is then precipitated, as eutectic phase, in the interdendritic regions. Under quiescent casting conditions grain refinement does not occur with concentrations of boron sufficient to refine plasma-melted material, although again the boron precipitates interdendritically. Grain refined samples forge with very little cracking under conditions which result in extensive cracking in non grain refined samples. Zener pinning of the grains by the borides ensures that grain growth in the forged and forged plus heat treated material is very slow. These results are discussed in terms of the importance of grain refinement in TiAI-based alloys.

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The synthesis of solid state materials has traditionally been accomplished using rigorous heating treatments at high temperatures (1,000°C) to overcome the slow rate of diffusion between two reactants. Re-grinding and re-heating treatments improve the rate of reaction between two solids; however, the high temperatures required to overcome the diffusion barrier limit the products accessible to the most thermodynamically stable phases. In this work, nano-scale solids such as alloys and intermetallics were synthesized via solution techniques where metal compounds are reduced by NaBH4 or n-butyllithium at temperatures below 300°C. To form hollow particles, metal nanoparticles of Co, Ni, Pb were synthesized via reduction by NaBH4 in water and reacted with K2PtCl6, which resulted in the formation of alloys in the case of Co-Pt and Ni-Pt. PbPt intermetallic hollow particles were synthesized by heating a composite of PbO and hollow Pt nanoparticles in tetraethylene glycol (TEG) at 140 °C. With n-butyllithium as a reducing agent, Au3M (M= Fe, Co, Ni) nanoparticles could be synthesized as isolatable solids in the L12 structure. PtSn and AuCu3 intermetallics were synthesized using NaBH4 and TEG. The PtSn and AuCu3 nanoparticles were characterized by transmission electron microscopy in attempts to learn about the phase diagrams of nanoscale solids. The purpose of this work was to synthesize nanoparticles via solution-mediated routes at low temperatures in compositions and morphologies not observed in the bulk, and learn about the phase diagrams of nanoparticles to understand why it is possible to access solids at temperatures significantly below those used in traditional solid state chemistry.

Al-rich Fe-Al systems (FeAl2, Fe2 Al5 and Fe4Al13) and Al20V2Eu have complicated structures with quasicrystal-like features making these materials potentially of interest for magnetic behavior. However, there is not much work on these materials. To study the variety of magnetic properties, we use NMR, magnetic susceptibility, specific heat and other methods in this work. The microscopic electronic and magnetic properties of the Al-rich Fe-Al system and Al20V2Eu have been studied via 27Al NMR at temperatures between 4 and 500 K. The results of spin lattice relaxation rates reveal a pseudogap in Fe4Al13 and Fe2Al5 around the Fermi-level in the density of states. Besides, a square well gap with a width of 2 meV and center at Fermi energy was detected by specific heat measurements in Fe2Al5. Both Fe4 Al13 and Fe2Al5 are non-magnetic systems with dilute magnetic defects, while FeAl2 is a concentrated local magnetic moment system. In Al20V2Eu, a crossover was observed in NMR, magnetization and transport measurements. Above 40 K, Eu(2+) local magnetic moments dominate; below 40 K, a transition to a Kondo regime is observed, where the Kondo effect leads to the reduction of localized moments due to the formation of a spin-compensated Kondo cloud. With increasing magnetic field, f electrons participate more and more in excitations near the Fermi level and a heavy-Fermion state was observed through specific heat measurements at high magnetic field.

Cast iron and steel alloys are commonly used for tooling and structural components in Al production, Al die-casting and the aluminizing industry due to their favourable properties including high strength, good formability and low cost. However, the iquid Al corrosion of these materials is one of the crucial concerns in maintaining the efficient production. Al is produced by the electrolytic smelting of alumina. Cast iron and/or cast steel pipes - commonly known as „tapping pipes‟ - are used to extract the liquid Al produced by smelting. Tapping pipes mainly degrade by material loss because liquid Al reacts with nearly all metals. Failure of tapping pipes is a significant contributor to the maintenance expenses; therefore, the primary aim of this research is to develop a material to enhance the life time of tapping pipes. Various test methods were developed in order to examine the effect of molten Al environment on cast iron and steel alloys. The corrosion resistance of these alloys was determined under different conditions of Al flow and temperature. The intermetallic compounds formed by exposing the ferrous to liquid Al were characterized using the Energy Dispersive X-ray Spectroscopy (EDS) and Electron Back Scatter Diffraction (EBSD) techniques. The formation, growth and nature of reaction products were revealed to establish a link to the liquid Al corrosion resistance. A relationship between the chemical composition and liquid Al corrosion resistance of cast irons could not established in the past. In the present work, the corrosion rate was found to depend upon the graphite morphology and fraction of each Fe-C phase of cast iron matrix, which can be controlled by selecting the chemical composition. Moreover, present research suggested the guidelines for producing a cast iron with enhanced liquid Al corrosion resistance. The presence of C-rich phases, graphite flakes and cementite was found to be effective in enhancing the liquid Al corrosion resistance of gray cast irons. Conversely, a higher Si content was found to enhance the susceptibility of cast irons to liquid Al corrosion. The corrosion mechanisms for ferrous alloys in liquid Al are not fully understood. Thus the subsequent analysis of the dissolution data was supported by investigating the reaction products formed between Al and substrate materials. In addition to commonly existent ε-Fe2Al5 and ζ-FeAl3 phases, the formation of Al4C3 and κ-Fe3AlC compounds was confirmed for the first time in the intermetallic layers of ferrous alloys. The Fe3Si phase in the intermetallic layers of high Si cast irons was found, which was believed to facilitate the high corrosion rates of high Si cast irons. Moreover, the mechanism by which C in Fe-substrates affects the liquid Al corrosion resistance can be better understood given the present work. Furthermore, the analysis presented here gives an understanding of the nature, growth and dissolution of intermetallic compounds in several cast iron alloys. Higher Si additions to cast irons played an important role in molten metal corrosion by accelerating the material loss and changing the nature of intermetallic layers. The results of this study clearly indicated that the dissolution and the growth of intermetallic compounds are interrelated and the dissolution and/or spallation of the intermetallic layers may be the primary mode of liquid Al corrosion of ferrous alloys.

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No description available.

With a view to design processes based on gas-solid reactiontowards the production of fine-grained novel alloys andintermetallics, studies of the reduction of the mixed oxides ofFe and Mo by hydrogen towards the production of Fe-Mo alloyshave been carried out in the present work. The route offersexcellent potentials toward the bulk production of nano-grainedmaterial of tailored-composition in bulk in a green processpath. As a case study, the reduction of the mixed oxides ofiron and molybdenum were carried out from the viewpoint ofmaterials processing, chemical reaction kinetics, as well asmechanical and structural properties. The reduction kinetics ofthin layer of fine oxide particles of Fe2MoO4 was studied usingthermogravimetric technique. This technique allowed determiningreduction parameters such as temperature of reduction as wellas the activation energies for the chemical reaction as therate-controlling step. The end products were analyzed by X-raydiffraction. The reduction product was found to be reduced topure, homogeneous Fe2Mo. In order to examine the upscaling ofthe process, production of the alloy in larger amounts wascarried out in a laboratory-scale fluidized reactor and theprocess parameters were optimized. It was found that, under theconditions of the experiments, the chemical reaction was therate-controlling step. TEM, SEM and X-ray analyses of thereaction product showed the presence of a monolithicintermetallic with micro- and nanocrystalline structure. Themechanical properties of this alloy were determined.Compositions of microcrystalline Fe-Mo alloys were varied byreducing mixtures of Fe2MoO4 with MoO2 or FeO with differentFe/Mo ratios. The products after the reduction consisted of twophases, viz. intermetallic FexMoy compound and metallic Fe orMo. XRD analyses revealed that the former had microcrystallinestructure while the latter were in crystalline form. This workshows that gas-solid reaction method, together with powdermetallurgy technique is a promising process route towards theproduction of novel metallic alloys such as Fe2Mo intermetallicwith micro- and nanocrystalline grains. <b>Key words</b>: nanoalloys, intermetallics, iron-molybdenumalloy, hydrogen reduction, thermogravimetry, fluidized bed,mechanical properties, structure