Materials Science Forum Vols. 727-728

Abstract: This work presents the structural comparison of Al₉₀Fe₇Nb₃ alloys obtained by different techniques: (i) partly amorphous powder alloy produced by mechanical milling and their consolidation by hot extrusion (cylindrical bar), (ii) from millimeter portion by casting centrifuged system (square shape), and (iii) from millimeter portion by melt-spinning (ribbon shape). The cylindrical consolidated alloy presented an Al matrix with Al₃Nb and Al₁₃Fe₄ nanophases (intermetallic compounds), the square consolidated alloy resulted in the same structure composed of Al matrix with Al₃Nb and Al₁₃Fe₄ in micro-phase scale. On the other hand, the ribbon alloy exhibits an amorphous matrix with primary Al nanocrystals (fcc-Al phase).

Abstract: This study aimed to produce nanometric powders of alumina by sol-gel route. Six samples were produced by varying the amount of water for dilution of aluminum nitrate and the calcination temperature. The final products were evaluated by thermogravimetric analysis, scanning electron microscopy, X-ray diffraction and particle size. It could be noticed that, beyond the time of gelation and calcination temperature, the addition of water also influenced the average size of the clusters.

Abstract: rradiation targets with 20% of ²³⁵U (Low Enriched Uranium - LEU) have been studied to replace HEU (Highly Enriched Uranium) targets in future nuclear reactors. These are used to produce the pair of radionuclides ⁹⁹Mo / ^99mTc, used for diagnostics in nuclear medicine. This work aims to develop an alternative route to produce LEU targets. It consists in hydrogenating and powdering metallic uranium and compacting the produced powder, followed by sealing it with nickel by electrodeposition. The deposited nickel should suppress the release of fission gases, and avoid a reactive contact of uranium with aluminum from the enclosure. In order to obtain the best conditions for deposition over uranium, in this work iron powder was compacted into small discs, with a diameter of 22mm and weight of 14g, simulating an equivalent volume of 10g of LEU uranium powder. As well, aluminum discs were used to ensure adhesion and uniformity of the nickel layer. Pulsed nickel electrodeposition was carried out over the compacts, employing current frequency of 900Hz, -0.84A/cm² of peak current and duty cycle of 0.5 in Watts Bath. The electrical resistance of pulse Ni-plated layer was checked by experiments with impedance spectroscopy in plated samples using aluminum substrate, held in KCl (pH=6), giving EIS results after resting the discs in solution for 0h, 4h and 24h. The physical strength was evaluated qualitatively by treating the Ni covered compact at 600°C, developing a bump deformation on the original planar layer, up to the point to open the Ni-layer for gas relief. These results suggest an adequate mechanical strength of the Ni-layer for using under neutronic irradiation, sealing the radioactive gases, mainly ¹⁴⁰Xe, produced during fission of ²³⁵U.

Abstract: Hydrocyclones are devices used in solid-liquid, liquid-liquid, and solid-liquid gas separation process applied in several industry fields such as mining, food and petrochemical. With the rising need of diminishing energy consumption and enhancing process efficiency, modifications on these equipments have been proposed in order to elevate their performance. It can be found in literature optimized geometric relations for a hydrocyclone (designated CH₁₁), aiming to conjugate low energy consumption and small cut size diameters. Hence, the purpose of this paper is to study the influence of filtration on CH depending on where the filtering wall is settled (cylindrical or conical part). The main experimental results suggest that the placement of the permeable region (conical or cylindrical parts) influenced the performance of the equipment regarding the main variables. In conclusion, setting a filtering wall brought expressive changes for the separation process.

Abstract: The self-reducing agglomerates produced from powders generated within the electric arc furnace and LD converters is of special interest in process of recycling due to the amount of iron and other metals of high economical value. However, the reducibility and inner pore structures play important role on the processing technology of these materials. Aiming at investigating the influence of the agglomerate structure, some two-dimensional metallographic techniques have been used to evaluate the porosity in clusters with inaccurate results, essentially due its three-dimensional features. From the processing technological point of view, the shape and distribution of inner porosity of the powders agglomerates are of fundamental importance due to their effects on the reaction rates involving the present phases taking place into the reduction stage. In this study a 3D serial sectioning imaging reconstruction is proposed to determine local inner porosities and detailed measurements of parameters of pores connections and tortuosities. The averaged porosities results are discussed and compared with traditional measurements based on pycnometry method.

Abstract: The objective of this work was based on catalysts Pt, Ni and Ru supported on zeolite NH₄ZSM-5 and characterize them. In this work monometallic bifunctional catalysts were prepared (Pt/NH₄ZSM-5; Ni/NH₄ZSM-5; Ru/NH₄ZSM-5), all containing the same concentration of each metal supported by competitive ion exchange, using solutions of platinum complexes [Pt (NH₃)₄] Cl₂, Nickel [Ni (NH₃)₆] Cl₂ and chloride Ruthenium III (RuCl₃). The samples were characterized by chemical analysis by X-ray Spectroscopy Energy dispersive (EDS), X-Ray Diffraction (XRD), nitrogen adsorption (BET method). Through the analysis of X-ray diffraction, its possible to identify the preservation of the structure of zeolite ZSM-5 after the competitive ion Exchange with metals (Ni, Pt, Ru) and calcination. The dispersion of platinum and ruthenium in zeolite ZSM-5, didnt modify the textural characteristics of the zeolite, but the dispersion of nickel caused a change in values of surface area of catalysts.

Abstract: Multilayer coatings are synthetic structures constituted by alternate layers of different materials. The technological applications of the multilayer coatings can involve optical, electromagnetism and wear areas. The target of this work is the production of multilayer TiN/ZrN coatings by Electron Beam Physical Vapor Deposition (EB-PVD) over titanium alloys produced by powder metallurgy. P/M-Ti-35Nb-7Zr-5Ta cylindrical samples used as substrates were produced by mixing of the elemental powders with subsequent cold pressing steps and sintering at 1400°C, in high vacuum. TiN/ZrN coatings were obtained by evaporation of alternating Ti and Zr cylindrical targets. The multilayers were characterized by optical and scanning electron microscopy (SEM), chemical analysis via energy dispersive spectrometry (EDS) and Vickers indentation. Besides the possibility of obtaining several layers, the results show coatings with coherent columnar structure, low discontinuity, large and homogenous thickness and high adhesion to substrate.

Abstract: During the recent years, alloys based on the intermetallic compound TiAl have attracted a considerable interest as potential competitors to steels and superalloys. Gamma-TiAl alloys are potential replacements for nickel and conventional titanium alloys in hot sections of turbine engines, as well as in orbital platform vehicles. The alloy design and efficient routes of TiAl processing are important technological challenges. Powder metallurgy is a near net shape process that allows the parts production with complex geometry at low costs. In this work, samples of Ti-48Al-2Cr-2Nb (at.%) were prepared from elemental and pre-alloyed powders mixed for 2 h, followed by cold uniaxial and isostatic pressing and sintered between 800 up to 1400°C, for 1 h, under vacuum. After metallographic preparation, sintered samples were characterized by SEM (Scanning Electron Microscopy), density analyses and Vickers microhardness measurements. The results indicated the viability of the pre-alloyed route and the tendency of a full lamellar microstructure of alternating gamma and α₂ phases in high sintering temperatures.

Abstract: The search for alloys with improved high-temperature specific strength and creep-resistance properties for aerospace applications has led in the last decades to sustained research activities to develop new alloys and/or improve existing ones. Titanium and its alloys are excellent for applications in structural components submitted to high temperatures owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability. Its high creep resistance is of great importance in enhancing engine performance. However, the affinity by oxygen is one of main factors that limit its application as structural material at high temperatures. Materials with adequate behavior at high temperatures and aggressive environmental became a scientific requirement, technological and economically nowadays. The objective of this work is the mechanical and microstructural characterization of the Ti-6Al-4V alloy after treatment by nitrogen Plasma Immersion Ion Implantation (PIII) process. The aim of this process is the improvement of superficial mechanical properties of the Ti-6Al-4V alloy. The selected alloy after ionic implantation process by plasma immersion was submitted to creep tests at 600 °C, in constant load mode at 250 and 319 MPa. The techniques used in this work were optical microscopy and scanning electronic microscopy. The fractograph analysis of the samples tested in creep shows narrowing phenomena and microcavities. The creep results show the significant increase of material resistance, it can be used as protection of oxidation in high temperatures applications.