Materials Science Forum Vols. 498-499

Abstract: Powdered steel reinforced by NbC dispersed particles was sintered both in resistive furnace at 1180°C or in plasma reactor at 850°C (reference temperature) using heating rates that ranged from 10 to 100°C/min. Fe3P was used as liquid phase sintering additive. The microstructure of the resulting materials was visualized by scanning electronic microscopy. Distinctive microstructural features were observed as a function of the heating source and heating rate. Plasma sintering at rates ~ 30°C/min revealed different microstructural features comparing edge and sample bulk. Homogeneous mixtures of Fe and NbC could be sintered in resistive furnace and plasma reactor using relatively low heating rates. Plasma sintering at 800°C for 1 h (heating rate of 10°C/min) resulted in relative densities of ~ 91% of the theoretical density of the composite. Sintering in resistive furnace for 1150°C resulted in relative densities ~ 94%.

Abstract: Considering its advantage of low density and favorable insulation properties, there are several applications for lightweight autoclaved aerated concrete of uniform cellular structure.The raw materials for the manufacturing of cellular concrete are Portland cement, finely grounded sand and lime. These are batched and mixed with water and metallic aluminum powder finely divided. There is a reaction between the aluminum powder and hydroxides forming millions of hydrogen bubbles throughout the mixture.The aluminum powder is the highest cost component, and the objective of this work is replacing it for another gas forming agent, like recycled foil.The foils are grinded in a high energy ball mill (attritor). Quartz sand is mixed with aluminum foil to reduce the time required for grinding, obtaining spherical particles and ensuring a uniform distribution of aluminum in the gas forming agent.The activity of this gas forming agent was determined by the gas volumetric technique. Average particle size and compressive strength of the samples were measured. The relationship between volume of the gas released during the reaction and milling conditions are presented, showing its viability for producing a high quality cellular concrete.

Abstract: The two major working characteristics of the oil control ring are: 1) to scrape the lubricant oil from the cylinder wall to the direction of the crankcase, and 2) to maintain a sufficient amount of lubricant oil to the compression rings above it in order to sustain a suitable lubricant film thickness between the rings and the cylinder. The oil control ring efficiency is the outcome of the combination of the following parameters: conformability, sort of the contact between the ring and the cylinder, contact pressure, and oil scraping dynamics. This work shows the development of an original oil control ring named Monoland, conceived by powder metallurgy design, having high conformability and optimized contact pressure that provides a superior oil scraping efficiency even with decreasing the friction losses. These qualities were achieved as an effect of an extensive product advance program established by Mahle Metal Leve Research and Development Center and Mahle Metal Leve Miba Sinterizados, which involved steps beginning from the product concept to the production streamline and passing through an extensive product validation program.

Abstract: Powder compaction characteristics is a very important parameter to control in order to obtain products with best mechanical properties made by P/M techniques. This work presents a study on the densification of titanium powders trying to optimize the particle size distribution for the best packing and the maximum densification by pressure compaction. The powders used were made from titanium sponge obtained by the Kroll process. The powders were embrittled by mean of the Hydride-Dehydride process (HDH) and milled in a rotative ball-mill under vacuum. Powders with different particles sizes distributions were mixed in several proportions according to Alfred's and Andreasen’s Theory. The samples were compacted by uniaxial and isostatic pressing and sintered under vacuum. The evaluation of the densification was made following the Standard method of test for density of glass by Buoyancy (ASTM – C693-74) and by scanning electron microscopy (SEM). The samples made with powder milled during 36 hours and 12 hours presented better densification than the ones milled during shorter time and the ones with distributions combinations.

Abstract: Austenitic stainless steel filters are mostly used when there is an aggressive environment condition, especially when good corrosion and mechanical resistance at relatively high temperature are required. These filters are usually obtained from non-spherical, mostly atomized powders by cold pressing and sintering. In order to achieve an adequate performance concerning permeability, powders with a narrow range of particle size should be used. However, besides particle size distribution, apparent density of the selected powder, which can be adjusted by the particle size, shape and distribution, affects the performance of the final product. Particle size distribution, particle shape and particle surface roughness control apparent density. This work presents some results on the evaluation of such effect.

Abstract: Diamond composites consist in the diamond powder mixed with a binder phase, which sintering is carried out by means of the High Pressure-High Temperature (HPHT) techniques. These composites are widely used in the cutters of drillers for the oil industry, and as inserts for machining. In this work was used a mix of diamond + 5% weight cobalt. Sintering was accomplished under the HPHT Lowest Limit conditions: P=7GPa and T=15000C for times of t=10-30-60 seconds, aiming at the densification study under these conditions. Results are shown as a function of the sintered micro-structure evolution, cobalt influence on densification, graphitization, and hardness of the sintered parts.

Abstract: Hardmetal is usually processed by the conventional powder technology techniques: mix of WC + Co powders compacted and liquid phase sintering. A new method to process hardmetal parts is hereby described. Parts of WC-15%wt Co were processed by using high pressure – high temperature sintering. It was used the pressure of 5GPa, temperatures of 780-1200-1350-1400oC, and times of 2-4 minutes of sintering. Results are shown as a function of micro-structural evolution, densification, and hardness measurements.

Abstract: Hardmetal is usually processed by the conventional powder technology techniques: mix of WC + Co powders compacted and liquid phase sintering. A new method to process hardmetal parts is hereby described. Parts of WC-15%wt Co were processed by using high pressure – high temperature sintering. It was used the pressure of 5GPa, temperatures of 780-1200-1350-1400oC, and times of 2-4 minutes of sintering. Results are shown as a function of micro-structural evolution, densification, and hardness measurements.

Abstract: Powder metallurgy (PM) and spray forming (SF) have been reported as important alternative routes for tool steel production. The ability to promote refined and more uniform microstructures is their main advantages, leading to improved properties and larger isotropy. While PM application is a completely established technology, the SF process may be considered as a not totally explored field. Therefore, the present work aimed to study the potential of both processes, focusing at high-speed steel (HSS) production. AISI M3:2 highspeed steel was produced by conventional casting, spray forming and powder metallurgy. Conventional ingots and a 400 mm diameter SF billet were rolled to small diameter bars, with cross section around 110 mm. The PM material was evaluated in the as-HIPed condition, in comparative diameters. Large diameter HSS bars are used mainly in cutting tools, but are also applied in cold work tooling when high wear resistance is required. In the present characterisation, microstructures and bend test analysis were used, both in transverse and longitudinal directions. The results show that the as-HIPed PM material presents finer and more uniform carbide distribution, leading to a complete isotropy and higher toughness than conventional steel. In the SF material, carbides are also finer, have good distribution and the isotropy is considerably higher than that for conventional HSS.

Abstract: The material used in this work was produced by spray forming AA7475 aluminium alloy and co-depositing silicon carbide particles (20% volume fraction). The spray formed composite billets were hot extruded into round bars. The microstructure was examined in the as received and heat treated (annealed, aged, and overaged) conditions by scanning electron microscopy. Scanning electron microscopy revealed an extensive Mg2Si phase precipitation at the Al/SiCp interface due probably to Mg segregation from the matrix to the interface, during the heat treatments.