Materials Science Forum Vols. 660-661

Abstract: The deposition of copper onto acrylic resin powder in its self-convective motion by magnetron DC sputtering was examined in order to prepare granular polymeric spacers coated with the metal, aiming at enhancing the cell wall structure of sintered highly porous aluminum materials. The fabrication of sintered highly porous aluminum materials was carried out in an ordinary powder metallurgy processing combined with a space-holder method with the polymer-copper binary spacer granules prepared by powder-coating using the sputter-deposition technique. The effects of the sputter-deposition of copper onto the spherical polymeric spacers on cell structures of the sintered porous compacts were investigated. According to optical observations, it was found that the sputtered copper could be uniformly and adherently deposited onto the surface of the acrylic granules. According to EPMA analysis on the cross-section on a sintered porous compact, it was found that Cu atoms were distributed at the vicinity of its cell walls, concluding that cell wall structures could be enhanced by this processing. Therefore it was expected that the compressive properties of the sintered highly porous aluminum materials were also improved by this powder coating process.

Abstract: Milk of lime is used in the sugar industry for pH correction and as auxiliary of flocculation in bleaching of the sugar solution. Despite its intense use in sugar cane industry, the milk of lime is rudimentarily produced. The milk of lime badly produced adds great quantities of incrustation in process pipelines and equipments and increases its specific consumption in the process. To mitigate these undesirable effects it is necessary to prepare a milk of lime with appropriated chemical, physical and morphological characteristics. In this paper, several different suspensions of milk of lime were tested in bleaching of the sugar solution. These suspensions were characterized chemical, physical and morphologically and the results were correlated with the performance of the bleaching of the sugar solution. Experimental results showed chemical composition, reactivity, particle size, surface area and slaking process of quicklime affect greatly the quality of the milk of lime.

Abstract: The aim of this work is to obtain and characterize the Niobium Carbide (NbC) by a suitable high energy milling technique using a SPEX Mill vibratory type and niobium and carbon (graphite) powders. Since this carbide is scarced in the national market and it’s necessary to apply this NbC as a reinforcement in two molybdenum high speed steels (AISI M2 and AISI M3:2) object of another work motivated this research. The powders were submitted to a high energy milling procedure for suitable times and conditions and then were characterized by means of Scanning Electronic Microscopy (SEM) and X-ray diffraction (DRX) techniques. The ball-to-powder weight ratio was 10:1. The analyzed samples showed that the high-energy milling is an alternative route of the NbC synthesis.

Abstract: This article aims to assess the influence of the way of simulating monoparticles as just monoparticles or as a mixture of particles, the latter, unlike the first, considering the effect of particle-particle interaction. The Eulerian–Eulerian multiphase model is used in the computational simulation of fluid dynamics of spouted beds and compared with experimental data. A half column of cylindrical spouted bed with a full plane glass attached to the front open surface of the bed as the transparent window was used for observation and photographing. Images of solid flows were recorded using a high speed camera (2000 frames per second). Glass beads with a diameter of 0.00368, 0.005 and 0.00252 mm are used as bed material. The simulated characteristic fluid dynamic curves of spouted bed for 0.15 m static bed heights (Ho) were obtained with good agreement with experimental data when the monoparticles was simulated as a mixture of particles with mixture’s percentage of 50%. The same occurred for the simulation of vertical velocities of particles profile, that is, when the monoparticles was simulated as a mixture of particles with mixture’s percentage of 50% we observed a more approach to the experimental data. It was also observed that the air concentration distribution seem to be independent of the changing of the composition.

Abstract: Stainless steel (SS) powders are used in the preparation of sintered SS products. One of the applications of sintered SS products is as filters in the petrochemical and food processing industries. In these industries, the SS filters are subject to severe conditions associated with the removal of solid particles from the fluid. Hence, SS filters should have adequate mechanical strength and high corrosion resistance. Welding can be used to manufacture SS filters. In this study, sintered AISI 316L specimens were welded using the TIG (Tungsten Inert Gas) process. The weld joints were examined by optical microscopy and by scanning electron microscopy. Electrochemical polarization measurements were carried out to evaluate the influence of welding on the corrosion resistance of sintered filters.

Abstract: This study aims to evaluate the behavior of thermally sprayed coatings with the HVOF technique (High Velocity Oxygen Fuel), subject to tribological testing of reciprocal movement with the SAE 52100 flat steel pin, in accordance with ASTM G 133. The carbon with Cr2C3-25NiCr and WC-12Co were evaluated under conditions of intense surface fatigue. The microstructure and surface modifications were analyzed by optical microscopy and scanning electron microscopy. By using these techniques were possible to compare the modifications of the coatings under repeated loading conditions, and to expand the knowledge about wear mechanisms, mainly the adhesive one, present in several mechanical components, particularly in bearing and internal combustion engines. The coatings tested showed lower wear rate when compared to SAE52100 steel and equivalent behavior among the different loading conditions applied.

Abstract: In the rock-drilling industry, double layer polycrystalline diamond-hardmetal (Dia-HM) inserts for cutting tools are subjected to elevated levels of wear due to the high power involved in the process. A research performed by focusing on the wear mechanism has shown that the complexity of the actual industrial operation can be reproduced in laboratories. The present work developed a methodology to calculate the theoretical values of wear of drilling tools. The main parameter selected for this methodology was the amount of disaggregated rock. The information acquired through this methodology gives one a complete perspective about the application of Dia-HM inserts to be used in drilling tools.

Abstract: The present work comprises a study about the possibility of obtaining polycrystalline diamond cutters through a novel method of sintering both layers at the same time. This possibility was tested through the sintering of a diamond layer over a hard metal (WC+15wt%Co) support under conditions of 5.0 and 6.5 GPa of pressure and 1400 to 1600º C of temperature. The sintering conditions were imposed in two ways: directly, or with pre-sintering. The samples were tested by measuring microhardness, wear resistance, densification, and SEM. The results of the tests have shown the possibility of obtaining good quality inserts by sintering both layers of compacted powder.

Abstract: The technologies of superhard materials production, including those for industrial synthesis of diamond and cubic boron nitride at high pressure and high temperature conditions, depend on the operator experience. Moreover, these manually operated processes usually vary in terms of yield and quality of the final product. Owing to the design and construction methods of conventional high pressure devices (HPD), it has not yet been possible to adapt computerized systems for both research and industrial production. In this work, the synthesis of superhard materials was treated as a guided problem under uncertain pressure, temperature, time, and electrical power conditions using the theory of automatic commanded systems. This concept was applied to develop an automatic control for the hydraulic presses that generate the necessary force for the high pressure, based on variable sensors associated with computer programs that command the conditions inside the HPD.

Abstract: Inserts of drill bits used in perforation of wells are employed to cut many different kinds of stone. The material that shows the best performance on this application is the WC+Co+Diamond composite, obtained via powder metallurgy. However, heterogeneous microstructural aspects in these composites may impair their efficiency. On this work, WC+6%Co-based composites were obtained via high pressure sintering at 5.0 GPa, with diamonds, WC and Co powders. The particle size of the diamond was 400/315 μm, and for the WC and Co, 100/63 μm. Part of the samples also received 2wt%CrB2 as a doping agent. Wear tests were carried out in an abrasimeter with a maximum axial load of 50 kg. Linear and volumetric wear indices achieved values of 821∙10-6 g/m and 10.7 g/m3, that are superior to inserts produced via conventional powder metallurgy.