Materials Science Forum Vols. 591-593

Abstract: Research on determined alloys produced by metal injection molding has been done for cost reduction purposes through the use of powders with bigger particle size. However, regarding feedstock homogeneity, certain limitations are presented when coarse particles are used. For instance, homogeneity strongly influences rheological behavior of the feedstock and dimensional control of the sintered part. Therefore, the purpose of this work was to evaluate effectiveness of a modified binder system with the addition of a surfactant polymer which makes the feedstock more homogeneous. This study was carried out on a FeNiP alloy currently processed by MIM, where 50%wt of the iron powder was replaced with course powder having a particle size distribution of D90 less than 47 ,m. Effectiveness of binder systems using a Melt Flow Index (MFI) and the behavior of dimensional accuracy at sintered part were analyzed. Results showed more feedstock homogeneity and less dimensional deviation when a surfactant agent was used.

Abstract: There are various methods for testing the viscosity of MIM feedstocks and described in the literature, e.g. melt-indexer, capillary viscosimeter, etc. Typical factors taken into consideration for choosing a proper method for feedstock characterization are the costs and the time needed for measuring. The paper presents three methods which have been developed to check the feedstock consistency directly on the injection molding machine. The first method is based on a slit-die rheometer. The second method considers the energy which is needed for conveying the melt inside of the plastification unit. And the third method is similar to a melt indexer but also in this case the measurement is done directly on the injection molding machine. These novel methods are suitable to detect inconsistencies in feedstock preparation.

Abstract: The production of titanium parts from powder metallurgy is one of the tendencies of modern metallurgy, since it allows obtaining structures with complex geometries and controlled porosity. The purpose of this study was to produce two types of dental implant prototype, and compare them biologically. Smooth surface prototypes were obtained, by the conventional turning process and porous surface prototypes using Metal Injection Molding (MIM). The prototypes were implanted in rats that were euthanized after 3 weeks, and the bone/implant interface was analyzed. The results showed that all prototypes were clinically stable at the end of the healing period, but those produced by the MIM process presented a significantly higher percentage of osseointegration (bone/implant contact) than the milled prototypes in the same healing period. It is concluded that the bone tissue grew independent of type of implant, enabling quick, rigid fixation already in the third week of the healing process.

Abstract: The work presents the research results of modern composite materials. The matrix material was EN AC AlSi12 alloy while the reinforcement ceramic preforms, obtained through sintering process of Al2O3 Alcoa CL 2500 powder with addition of carbon fibers as pore forming agent burned out during sintering. The composites were produced with use of porous material pressure infiltration method. The main limitation of base technology is a difficulty in obtaining composite materials with volumetric participation of ceramic phase in amount not less than 20%. Obtained on the base of ceramic preforms composite materials were tested with scanning electron microscopy. Additionally, hardness and tensile test was performed for acquired materials. Achieved results indicate the possibility of producing, with use of pressure infiltration method, porous preforms composed of Al2O3 particles, new composite material with desired microstructure and properties, being a cheaper alternative for materials with base of ceramic fibers.

Abstract: Powdered uranium silicide (U3Si2) 20% U235 enriched is an intermetallic compound used as nuclear fuel material dispersed in aluminum to be the meat of fuel elements. U3Si2 powder is the state-of-the-art as nuclear fuel material mostly used in modern research reactors. Its recent established fabrication in IPEN replaced the previous ceramic powder U3O8 used in the fuel of IEAR1 (IPEN/CNEN, São Paulo, Brazil). The U3Si2 is a compound with 92.3%wtU and 7.7%wtSi. Its production is made by induction furnace melting using metallic uranium, produced by magnesiothermic reaction, and pure silicon. The induction furnace melts under argon controlled environment using zirconia crucible. Homogenization of liquid bath at 1800°C is a compromise between crucible resistance and homogenized melting, avoiding hazardous happenings. IPEN produced its first lot of enriched U3Si2 in September 2004, with a continuous fabrication ever since. This research work represents the ability of having fully Brazilian supply of this strategic and high cost nuclear material. The fuel quality meets the world quality standards required by International Atomic Energy Agency (IAEA) and RERTR standards. Brazilian production of U3Si2 powder not only closed the fuel cycle, from uranium mineral to fuel element, but also allowed higher productivity of nuclear medicine radioisotopes by IEA-R1.

Abstract: Gamma uranium-molybdenum alloys has been considered as the fuel phase in plate type fuel elements for MTR reactors due to its performance under irradiation and metallurgical processing. To its usage as dispersion phase in aluminum matrix, a necessary step is the conversion of the as cast structure into powder, and the technique considered at IPEN / CNEN - Brazil was HDH (hydration-dehydration). This work has the aim to study the hydrogen incorporation by gamma-UMo alloys with 8% weight molybdenum. The samples were thermally treated under constant flow of hydrogen, for temperatures varying from 500oC up to 600oC and times of 1 to 4 hours. Some of the curves relating mass incorporation and time for the above temperatures were obtained, and the results related to its microstructures and ease of fragmentation.

Abstract: Scrap tire is considered an environmental concern with inadequate final disposal. A good alternative can be to use the tire as an energy source. Pyrolysis is a thermal process that can transform the rubber portion of used tires into oil, gas and pyrolytic carbon. This type of carbon can be converted into carbon black (CB). The lime industry that demands great amount of energy could be one of the ways to take advantage the scrap tires adequately as energy source. This work aimed to study the operational conditions of the pyrolysis process as well as investigating the possibility to use the pyrolysis products from used tires as industrial fuel. A batch pilot-scale pyrolysis unit was built. Temperatures from 400 to 600oC and relative pressures from 0 to -500 mmHg were investigated in order to evaluate product distribution and quality. Experimental results showed that as the reactor temperature was increased the pyrolytic carbon yield remained constant with a mean of 39.8 wt % and the pyrolytic oil yield reached a maximum value of 45.1 wt % at 500 °C. It is also possible to show that the pyrolytic oil can be used as liquid fuels because of its high heating value (40-42 MJ/kg), excellent viscosity (1.6-3.7 cS), and reasonable sulfur content (0.97-1.54wt %). In addition, chemical and physical characterization was made in order to compare the pyrolytic carbon and oil with currently fuels used in Brazilian lime industries (wood charcoal and coke of petroleum).

Abstract: Recycle aluminum cans, an alternative route is presented in this work. The aluminum cans are cut in little flakes with a shears, and then the materials were milled, obtained fine powders. The weight ratio of the balls to powder was 10 to 1. Equipment of a horizontal high energy ball mill was utilized. The powder mixture was processed during 0.5, 1 and 2 hours at 950 rpm and after milling, the powders were directly hot extrusion. The extruder bars were submitted at a tensile tests and samples microstructures were analyzed by optical microscope. Experimental results obtained shows that the technique utilized in this work is very important for economized routes and consequently, less expensive, as compared with conventional methods.

Abstract: Powder consolidation constitutes an important step in the manufacture of products of high quality and precision. To obtain these components, with desired forms and final mechanical properties, it is of extreme importance to have knowledge about the processes to obtain powders, compacting and sintering. The objective of this work is to verify which model, obtained from the literature, better describes the compaction densification behavior of iron powder in closed-die. Doraivelu’s criterion was carried through the method of the finite elements with the implementation of an elastoplastic model with hardening. The influence of the yield function coefficient against the relative density was evaluated, as well as, the yield function in the hydrostatic space.

Abstract: Ti-35Nb-7Zr-5Ta alloy is a promising new material for a bone graft substitute with good strength properties and an elastic modulus closer to that of bone than any other metallic material. TNZT samples until 50 vol % porosity were manufactured using ‘‘space holder’’ technique and sintering methods. Irregular ammonium carbonate powders were used as a space holder material. Complete removal carbonate from the green compact was achieved by heating at 200 °C for 5 hours and subsequent sintering at 1600 °C, with heating rate of 10 °C/min. For the alloy microstructural characterization, scanning electron microscopy was used. Density was measured by Archimedes method. The results show that the blended elemental P/M process and the space holder technique are efficient for the obtainment of highly porous samples. Foams with porosities in the range between 10% and 50% could be reached.