Materials Science Forum Vols. 727-728

Abstract: Removed by author's request

Abstract: The synthesis of advanced materials with superior performance and properties is of growing scientific and technological interest. In particular, significant achievements have been attained in the synthesis of nanocomposites associated with superhard materials. This work investigates nanostructured composites obtained by high pressure and high temperature sintering of synthetic diamond combined with boron, silicon and copper. Diamond powder was mixed with B, Si and Cu, also in the form of powder. The mixture was then submitted to high energy wet milling until a nanopowder was formed. Sintering of this resulting nanopowder was carried out at 5.6 GPa of pressure and 1300°C. X-ray diffraction and scanning electron microscopy analysis revealed the formation of new phases in a well consolidated nanostructure with relatively high density.

Abstract: This work presents the evaluation of the use covering with carbon black to replace the graphite covering used in previous work, aiming to eliminate the grinding step to the process. The results of this treatment were characterized by optical microscopy, scanning electron and hardness. The micro hardness achieved was near to 760 HV _0.05, coefficient of friction of 0.2. Scanning electron microscopy showed that the extent of the treated area by laser reaches near to 90μm, and the thickness coating of carbon black is about to 2μm. The graphite can be substituted by carbon black, acting as coupling of the laser beam radiation, and as a solid lubricant, according to REIS (2009).

Abstract: In this work low carbon steel samples were coated by tungsten carbide (WC), and then the properties of the obtained coatings were evaluated, such as morphology, hardness, phase composition and dimension of the layer. The results indicate the formation of a new phase, composed of iron carbide in the base metal, a more dense coating has been obtained when the WC powder was sprayed directly on to the steel and then irradiated with the laser beam.

Abstract: Synchronizer rings are mechanical components that equalize the gear rotation to be engaged with the sliding sleeve. It is done by the friction property of the synchronizer ring material. Different types of materials are used to manufacture synchronizer rings depending on the application. There are basically two groups of material: dual function, structural and friction properties (Cu-Zn alloys, Al-Si alloys, etc.) and single function, only structural property (rolled and sintered steels, Cu-Zn alloys, Al alloys, etc.). The objective of this work was to propose a solution to the synchronizer ring structural material of a new mechanical transmission design. This component was initially designed with a Cu-Zn alloy and showed premature failure on synchronizer teeth during tests. To eliminate this problem several technical alternatives were analyzed considering the best cost and benefits ratio, defining to use the sintered steel FLC-4908 per MPIF Standard 35.

Abstract: In the fabrication of nuclear reactor core parts, machining chips of Zircaloy are generated. These alloys are strategic for nuclear technology and cannot be discarded. In the present work are presented two methods for recycling of Zircaloy chips. One of the methods is by melting in VAR furnace and the other by powder metallurgy method. By this method the Zircaloy was submitted to hydriding process and milled in a high-energy ball mill. The powder was cold isostatically pressed and vacuum sintered. The elemental composition of the samples obtained by both ways was determined by XRF and compared to the specifications. The phase composition was determined by XRD. The microstructures resulting of both processing methods, before and after rolling were characterized using optical and scanning electron microscopy. The good results of the powder metallurgy method suggest the possibility of producing small parts, like cladding cap-ends, using near net shape sintering.

Abstract: For the last 30 years high uranium density dispersion fuels have been developed in order to accomplish the low enrichment goals of the Reduced Enrichment for Research and Test Reactors (RERTR) Program. Gamma U-Mo alloys, particularly with 7 to 10 wt% Mo, as a fuel phase dispersed in aluminum matrix, have shown good results concerning its performance under irradiation tests. Thats why this fissile phase is considered to be used in the nuclear fuel of the Brazilian Multipurpose Research Reactor (RMB), currently being designed. Powder production from these ductile alloys has been attained by atomization, mechanical (machining, grinding, cryogenic milling) and chemical (hydriding-dehydriding) methods. This work is a part of the efforts presently under way at IPEN to investigate the feasibility of these methods. Results on alloy fabrication by induction melting and γ-stabilization of U-10Mo alloys are presented. Some results on powder production and characterization are also discussed.

Abstract: The powder metallurgy processing of titanium devices for biomedical applications has complex steps. In order to introduce a new processing route, this work studied a sol-gel technique combined with powder metallurgy for producing porous titanium samples. The process involves the mixture of titanium powders with sodium alginate suspension, which undergoes reticulation by calcium salt solution contact, forming a titanium/calcium alginate hydrogel in granule shape. Later, the hydrogel granules were dried and sintered in a high vacuum furnace for titanium particles consolidation and calcium alginate removal. The samples characterization was performed by scanning electron microscopy, optical microscopy, metallographic analysis, semi-quantitative X-ray fluorescence spectroscopy and X-ray diffraction. The results showed that the methodology used is adequate for producing porous titanium parts, since the samples presented no contamination, a uniform shape, particle consolidation and interconnected porosity. The research continues aiming to obtain samples with different bulk morphology, like, discs or bars for surgical implant applications.

Abstract: The use of hydride powders in titanium powder metallurgy (P/M) is a low cost alternative for the manufacture of titanium alloys. However, due to the high reactivity of these powders, parts produced using this technique may contain interstitial impurities such as oxygen, nitrogen and carbon. In this work a factorial design approach was used to evaluate the influence of some stages of P/M upon the levels of these elements in sintered samples of Ti-6Al-4V. Milling time of titanium hydride powders, sintering temperature and holding time were evaluated. The effect of milling time was detected as the most significant for the increase in oxygen levels. The contents of all elements were affected by the increase of sintering temperature from 1200 °C to 1400 °C. Holding time was shown to be significant only for the carbon absorption in the samples sintered at 1400 °C.

Abstract: In this work the possibility of production of cemented carbide doped with rare-earth element (Y₂O₃) under condition of high pressure and high temperature (HPHT) was investigated. Initially, the cemented carbide powder (WC10wt.%Co) was submitted to conventional pressing at 800 MPa. The compacts were then sintered at 1400 °C for 40 s under a pressure of 5.5 GPa. The cemented carbide pieces were characterized in terms of relative density, coercive force, mechanical strength, microhardness, and wear resistance. The phase analysis was done by X-ray diffraction. It was established promising results on the production of cemented carbide under high pressure. Moreover, the addition of up to 1.5 wt.% of yttrium oxide in relation the cobalt phase enhanced the technical properties of the cemented carbide.