Materials Science Forum Vols. 530-531

Abstract: Aluminum alloys have been increasingly applied as a structural material in composite materials using metal matrix due to their excellent mechanical properties and low weight. The reinforcement are of fundamental importance in composite materials, owing to the their responsibility to support stresses acting on the metal matrix. Therefore, ceramic reinforcements can be replaced by intermetallic components with high mechanical properties and good thermal stability. The intermetallic components react chemically with the matrix, characterized by strong interactions, which makes possible the development of the new families of materials. The composite materials using aluminum reinforced with nickel aluminides and ceramic were developed using techniques based on a combination of powder metallurgy and extrusion processes, which makes possible to obtain more dense materials under lower processing temperatures. The powders of AA6061 and Ni3Al were manually mixed for 30 minutes, with different percentages of intermetallics and ceramics particles, 5 and 10% in weight. The composite powders were submitted to a hot extrusion process for 40 minutes at 540oC, and 385 MPa, with a reduction ratio of 25:1. This process insures extruded composites with a refined structure and a good distribution of the reinforcement particles. The material characterization were performed through structural analysis via scanning electron microscopy; mechanical behavior via tensile and hardening tests; and analysis of the fracture. The results show that the method used is effective to obtain composite materials with improved characteristics.

Abstract: Particle reinforced metal matrix composite (MMC) coatings have been developed due to property combinations such as increased hardness, high creep/fatigue resistance as well as superior wear and oxidation resistance. MMC coatings can be produced by various techniques, which include powder metallurgy (plasma spray and HVOF processes), liquid metal processes and electrodeposition. This paper presents the development of the electrodeposition process to obtain nickel-alumina composites. The process conditions were optimized and based on these gradient nickel-alumina composites were prepared. Microstructural characterization and hardness determinations were carried out. The effect of process parameters on the amount and distribution of alumina particles as well as morphology of the deposits with and without alumina gradients are presented and discussed.

Abstract: Investigations include alloying the X38CrMoV5-3 hot-work tool steel surface layer with the tungsten carbide, using the high power diode laser (HPDL). The tungsten carbide ceramic particles of the medium grain size according to FSSS = 50 Bm were introduced using the rotor conveyer to improve the properties of the surface layer. The powder feed rate was set at the steady level of 8.64g/min. Remelting and alloying were carried out several times in the laser power range of 1.2 – 2.3 kW in the remelting/alloying, alloying/remelting sequences. The structural mechanism was determined of gradient layer development, effect was studied of alloying parameters, gas protection method, and powder feed rate on its mechanical properties, and especially on its hardness, abrasive wear resistance, and roughness. Structure changes were revealed consisting, in particular, in its refining, and also hardness and microhardness changes in comparison to the non-remelted steel. Examination results obtained with the EDX microanalysis, surface and linear analyses of the chemical composition, as well as the X-ray qualitative phase analysis are presented.

Abstract: Nowadays, all PM part manufacturers are subjected to the huge pressure to reduce prices and minimize cost. Apart from the maximum utilization of the machines in multi-shift operation, the manufacturers have to select the optimum machinery in terms of pressing technology. Flat parts, for instance, are produced on mechanical high-speed presses with very high economic efficiency. Here high stroke rates that can be achieved are the focal point. Multi-level complicated components are produced on multiplaten presses providing hydraulic auxiliary movements. Both mechanical automatic presses with modular multiplaten die sets and hydraulic presses with closed-loop controlled movements, equipped with position sensors, are suitable for this application. The geometrical complexity, the requested dimensional tolerances and the density are of decisive influence of the machine to be selected. The sizing is process is carried out on machines providing optical part recognition and automatic part handling. For this wide variety of different applications DORST Technologies can offer customized plants to suit the requirements. To gain maximum economic efficiency, all machines – powder compacting presses or automatic sizing presses – are available with handling systems such as die set change systems, or linkage of the press with the furnace.

Abstract: This work develops a mathematical model that explains the ball mills operational speed. The scope of the model is defined by the powder as the number of particles per cm3 and the Relevance defined as the ratio between different forces. In this study, the Relevance is defined as the ratio between superficial tension and inertial forces. The conditions for a free flowing powder and a single particle are differenced and non-dimensional numbers are found. The model proposed use the friction force between mill walls and the powder mass is related by a friction coefficient that can be calculated from angle repose. An experimental approach proves that the suppositions made in order to develop the model were adequate in this way the existence of the non-dimensional numbers is confirmed. It is also discussed the use of non-dimensional numbers to increase processing speeds with by increasing gravity clarifying that a given Relevancy, it is not dependent of the non-dimensional numbers. Thus, the model can help in the design process of ball mills with a deeper understanding of the phenomena.

Abstract: The cyclones are one of the most known apparatus destined to the solid-gas separation. These equipments are used in the chemistry industry; its popularity is due mainly to the simplicity, low energy requirements and ability to operate at high temperatures and pressures. One of the aims of this work was to evaluate the influence of some geometrics variables in the performance of conventional cyclones and filtering cyclones. The chosen variables were: conic part length (Zc), the underflow diameter (Du), the overflow diameter (Do) and the finder length (Sc). The cyclones conventional and with filter were compared and it was observed that the introduction of a filter main in substitution to the metallic conic part of cyclones allows a appreciable reduction in the pressure drop and consequently a smaller consumption of energy. The efficiency in the new cyclone was a little smaller than the conventional equipment.

Abstract: Continuous Binder-Powder Coating (CBPC) is a new fabrication route for the titanium metal matrix composites reinforced with continuous SiC filaments. Based on powder-cloth process, this alternative fabrication route is characterised, analysed and application viability is discussed considering the other related routes. In addition, effects of the pressure and temperature on the Ti/SiC/C composites were considered for matrix consolidation. Results have shown that the titanium matrix composites processed by Continuous Binder-Powder Coating present, simultaneously, good matrix densification, consolidation and also a weak interaction between matrix and fibers, when the hot pressing is performed under 150 MPa at temperature below β-transus. Most important characteristics of the CBPC process and its application viability are reported, in this paper.

Abstract: The Venturi scrubbers have a high collection efficiency to remove very small particles from gaseous streams. The main purpose of this work is to determine the overall collection efficiency of Venturi scrubbers with circular section under different operation conditions. The experimental system consisted of a Venturi scrubber with circular section and liquid injection in the throat. A factorial experimental design was carried out; the overall collection efficiency was the response. Three variables were analyzed: the throat length, the air velocity and the liquid flow. The best values for efficiency were obtained for 15 m/s of air velocity and 300 mL/min of liquid flow and the throat length did not have influence.

Abstract: Osseointegrable surgical implants are usually made on titanium or titanium alloys. The osseointegration process is improved by surface conditioning of these implants, increasing surface area with no loosing of bio-compatibility, i.e., without contamination by non bio-compatible materials. The surface conditioning of these implants might be accomplished in different ways: blasting, chemical etching, deposition, etc. Two alternatives considering titanium powders are discussed in this work: blasting and plasma spraying deposition. Results are presented in terms of topography of osseointegrable surgical implants through scanning electron microscopy techniques.