Materials Science Forum Vols. 530-531

Abstract: Machining tools (interchangeable inserts) were manufactured from spray formed AISI M2 high-speed steel. The spray formed materials were mechanical and microstructural characterised. An assessment of the machining performance of the spray formed high-speed steel was attained. These results were compared to materials obtained by conventional and powder metallurgy techniques. The results showed that under the used process conditions (hot rolling and heat treating), the spray formed material showed a machining behaviour near closed to other materials; and highlight the potential of the spray forming technique for the obtention of materials with adequate properties for machining tools manufacturing.

Abstract: Cemented tungsten carbides were produced by liquid-phase sintering. In these work high energy milling (HEM) was used to produce homogeneous and finely grained powder mixtures. The milling effect on the magnetic properties of sintered samples is studied. Different mixtures in same composition (WC-10wt.%Co) were prepared by conventional mixture technique and wet HEM up to 300 hs in Planetary Mill. Magnetic hysteresis measurements on the sintered samples detected a significant increase in the coercitive field and a decrease on the saturation magnetization with milling time increasing. X-ray diffractogram show phase transformations with milling time. The Magnetic properties are correlated with phase relations and microstructural properties of the sintered samples.

Abstract: The objective of the present work is to study the manufacturing process of steels with high carbon content (1.5–2.1wt%) obtained by powder metallurgy. The reference material was the Damascus steel, which was employed to manufacture swords named after it and has been widely known due to its very good mechanical properties. The main reasons of the success of this product are: the high carbon content of the initial steel and the thermomechanical treatment (forge and quenching) that ancient iron forgers kept secretly during centuries. Different carbon contents (2 to3 wt%) were added to the same Fe powder matrix (ASC 300), and compacted and sintered steels are heat laminated (750°C) with a reduction of 20%. For 2% carbon content, the result is a steel with yield strength of 450 MPa, Young’s Modulus of 14.3 GPa and hardness of 109 HV(30).

Abstract: This paper presents the investigation results of laser alloying and the influence on structure and properties of the surface of the 32CrMoV12-28 hot work steel, carried out using the high power diode laser (HPDL). Structure changes were determined in the work, especially structure fragmentation. Also hardness investigation of the different remelting areas was performed. The reason of this work was also to determine the laser treatment parameters, particularly the laser power, to achieve good work stability and to make the tool surface more resistant for work extremal conditions. Based on microstructural examinations of the obtained material, the distribution of the reinforcing ceramic particles in the hot work tool steel was revealed. Tungsten carbide WC powder was used for alloying. The remelted layers which were formed on the surface of the investigated hot work steel were examined metallographically and analyzed using a hardness testing machine.

Abstract: Beta titanium alloys, e.g., are now the main target for medical materials. Ti-35Nb-7Zr- 5Ta alloy were manufactured by blended elemental (BE) powder method, which appears to be one of the most promising technique for titanium parts production at reduced cost. The process employs hydrided powders as raw materials with low production costs and oxygen content. Among the titanium alloys recently developed, Ti-35Nb-7Zr-5Ta is distinguished for presenting low modulus of elasticity, high mechanical resistance and superior biocompatibility. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering among 800 at 1500 °C, in vacuum. Sintering behavior was studied by means of dilatometry. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Density was measured by Archimedes method. In this work, an alternative blending technique (with planetary mill) was used. The samples presented a good densification and a totally β-type microstructure, with complete dissolution of alloying elements in the titanium matrix with the temperature increase with low pore content.

Abstract: This work presents the results of a study concerning the influence of the addition of rareearth elements (La2O3 and CeO2) on the sintering of the WC/10Co cemented carbide. Several WC/10Co mixtures containing up to 3 wt.% rare-earth of the cobalt phase were prepared. Specimens were uniaxially pressed at 200 MPa, and sintered in a vacuum furnace at 1400 °C during 60 minutes. The sintering behaviour was accompanied by the linear shrinkage, density, and mechanical strength. The development of the microstructure was followed by XRD and SEM. The results showed that the sintering behaviour of the WC/10Co cemented carbide was influenced by adding of rare-earth element. In addition, the lanthanium oxide addition was more effective on the improvement of the physical-mechanical properties of the studied carbide.

Abstract: Fabrication of sintered compact from aluminum powder coated with tin deposits was examined, in order to enhance the bonding among the aluminum particles under the assistance of tin and thereby the sintering effect of the aluminum powder, aiming at improving the mechanical properties of sintered aluminum materials. For the coating of aluminum powder with tin deposits, the deposition of pure tin onto the aluminum particles was carried out by magnetron DC sputtering during the self-convective motion of the aluminum powder in a vacuum chamber. The tablet consisting of the aluminum powder coated with tin deposits was sintered at 650°C in a vacuum chamber for 2 hours, while the tablet consisting of non-coated aluminum powder was also sintered under the same condition for comparison. The sintered compact from the coated aluminum powder was solid and uniform, and its consolidation reached over 95% while that from non-coated aluminum powder was around 85%. According to tensile tests, the tensile strength of the sintered compact from the coated aluminum powder was 75.4N/mm2 while that from non-coated aluminum powder was 71.0N/mm2, and the elongation of the sintered compact from the coated aluminum powder reached over 20% while that from non-coated aluminum powder was around 10%. Therefore it was found that the consolidation and the mechanical properties of the sintered compact consisting of aluminum powder were considerably improved by this powder coating process.

Abstract: Liquid phase sintering of high speed steels seems to be a cheaper processing route in the manufacturing of tool steels if compared to the well-known and expansive hot isostatic pressing high speed steels process. In a previous work a M3:2 high speed steel was vacuum sintered from irregular water atomized powders and had its sintering temperature determined. In this work the same powder was uniaxially cold compacted and vacuum sintered by adding some small quantity of graphite (0.3%C in weight) to prevent porosity and loss of carbon which result from the sintering cycle. The samples from all these experimental procedures were uniaxially cold compacted and vacuum sintered at five different temperatures and had its densities evaluated. The microstructure was evaluated using optical-electronic techniques in order to investigate the best range of sintering temperature. At least five parallel samples were tested to each condition of sintering.

Abstract: In this study, the results of the feasibility of sintering green compacts of metallic powder of MoSi2 by a CO2 laser beam as the heating source has been investigated. The main advantage of this technique is to promote a dense material in a reduced time when compared to the conventional sintering process. In order to sintering the MoSi2 powder, green compacts of 6mm of diameter and 1.6mm thickness were produced in a steel die in a uniaxial press at 100MPa and after, isostatic pressed at 350MPa. The micrograph of the samples exposed to the laser radiation performed by scanning electron microcopy (SEM) reveal the efficiency of the sintering process and the X-ray diffraction of the powders confirmed the presence of single phase after and before laser processing. The average microhardness of these compacts reached near to 700 Hv0.2 in the cross section to the laser irradiation, indicating the all sintering of the green compact.

Abstract: The Venturi scrubber is used for removing particulate matter from gaseous effluents and finds a large application in industry. The size of the droplet is of fundamental importance to the performance of the equipment. This work aims at studying the effect of some design parameters, namely liquid flow rate and liquid injection system in the droplet size and to correlate this with collection efficiency. A laser diffraction technique was used in order to measure droplet size in situ in a rectangular Venturi scrubber, with liquid injected through 1mm diameter orifices on the throat walls. Liquid flow rates of 600 and 900 ml/min and number of orifices varying from 1 to 5 were used in the experiments. The throat gas velocity was kept at 69.3 m/s. It was found that all these variables significantly affected droplet size. The results of droplet size were compared with the particle capture (collection) efficiency measured in the same experimental conditions. It was observed that the collection efficiency was affected by the liquid atomizing conditions and by the droplet distribution in the Venturi throat.