Materials Science Forum Vol. 672

Abstract: The elaboration of carbon steels sintered through the enrichment of compactised iron powders in carbon in methane gas medium has allowed the development of an innovative technology that fort he first time is based upon the carburizing (the process of carbon enrichment, in different proportions) at the same time with sintering. The parts obtained through this proceeding have been analysed from the point of view of the physical and the mechanical characteristic in correlation with the compaction pressure of the iron powder.

Abstract: Residual stresses play an important role in the performance of materials and the components produced from them. All manufacturing processes introduce residual stresses. These stresses can have a positive effect, for example by increasing the fatigue limit in the case of compressive surface residual stresses. Layer removal by electrochemical machining (ECM) can be used for measurement of the residual stresses in the PM parts. The device removed the layers by aid of electrochemical machining for this purpose is designed and developed. The device setup for residual stress measurement is based to the changes on deformation quantity. Since ECM is a non-mechanical metal removal process, ECM is capable of machining any electrically-conductive material with attendant high removal rates, regardless of mechanical properties. In particular, the removal rate in ECM is independent of the hardness, the porosity and toughness of the PM parts being machined. The micro constituents in PM steels resulting from different processing routes exhibit different thermal and mechanical behavior. This will lead to the formation of residual stresses around these micro constituents. Here we give the results of the first work carried out on PM steels in relation to residual stress measurements by the electro-chemical layer removal technique. The device works as follows. As a layer of thickness is removed, a certain amount of stress is removed from the sample. Equilibrium is violated and the sample deforms elastically to compensate for the stress removed. This elastic deformation in the sample is measured by the linear displacement gauge. This gauge pushes on the end of sample and deformation is recorded by this gage. The linear gauge send a signal to a display and then to the data converter. As simultaneous, this signal sent to the computer from the data converter for further calculations by RS 232.

Abstract: Shape memory Titanium-Nickel alloys, also known as Nitinol, are amongst the most utilized materials with special properties in the medical field. Together with the properties of shape memory and superelasticity, these alloys have a very good biocompatibility. In this study, the equiatomic Ti-Ni alloy was obtained in the form of alloyed powder, starting from elemental high purity powders, through mechanical alloying. Specimens for testing the mechanical characteristics of the material, as well as smaller samples for biocompatibility tests were manufactured. The latter ones were prepared for implantation on live tissue, on Wistar rats and Guinea pigs. The structure of samples was studied by microscopy and X-Ray diffraction analysis. All the results have demonstrated the presence of the TiNi intermetallic compound as the quantitative dominant phase. After applying an adequate thermo-mechanical treatment, the tested samples displayed measurable shape memory effect and superelasticity. The in vivo biocompatibility tests, done according to international standards, demonstrated the material’s bio-inertness in relation with living tissue. The obtained results have shown the possibility to elaborate Ti-Ni biocompatible alloys by mechanical milling and sintering.

Abstract: NiTi alloys, due to the special properties they posses, good corrosion resistance, biocompatibility, and shape memory, are used successfully in the medical field. The paper presents research concerning the elaboration of the NiTi alloy in the form of spherical shape powder with hollow particles. This type of powder would be the raw material for fabricating light weight products like prosthesis or surgical implants. The aim of the research was to elaborate this type of powder and determine the alloy’s phases in correlation with the need of obtaining a specific particle shape. Along with these aspects it was attempted to form different testing samples through sintering operations.

Abstract: Phospho-silicate glass powder consisting of particles sized up to 60 micrometers was incorporated into insoluble collagen by mechanical milling. After 8 hours milling at 180 rpm, the two phases are still separated. Increasing of mill frequency at 1800 rpm led to glass particles encapsulation in the collagen matrix after 90 minutes. The collagen structural properties after mechanical bonding to glass powder particles are investigated by vibrational spectroscopy in order to emphasize the milling effects upon the protein secondary structure.

Abstract: The paper presents a preliminary study on the obtaining of a composite powder by an electrolytic method. The composite powder particles are composed of iron nickel alloy that represents the matrix of the composite, and titanium carbide as the reinforcement. The matrix was obtained by electrolytic co-deposition from pure iron and nickel, in form of consumable electrodes. The titanium carbide powder is in suspension in the electrolyte. By the migration of metallic ions towards the cathode, the iron- nickel alloy is formed and, by simultaneously driving the carbide particles found in the electrolyte onto the cathode, the composite powder is obtained. The resulted composite powders were characterized by optical and electron microscopy. The influence of obtaining conditions over the morphology and structure of composite powders is emphased.

Abstract: Spherical bronze powders were used for studies the obtaining of gradual porous structures by sedimentation and sintering methods. The powder size classes above 100 μm were used for the manufacturing of the macroporous support by spreading the powder into the sintering die. Sintering was conducted in vacuum (10-4 Torr) at a temperature of 750 °C for 40 minutes. On the macroporous support a layer of fine powder fraction was deposited by gravitational sedimentation. The deposited layers were consolidated by sintering at 750 °C for 30 minutes. The analysis of the gradual porous layers was done using scanning electron microscopy and mercury porosimetry. The fluids viscosity influences the sedimentation velocity of particles. The height of the column directly affects the quality of porous structure. If the sedimentary column is short, the turbulences created by adding the suspension of the dispersed powder in the sedimentary tube are more harmful.

Abstract: In this work, hollow spherical nickel based superalloy powders obtained by liquid phase atomization were used. The obtained powder was divided into six size particle ranges between 200 µm and 630 µm using a shatter box. Samples from all six ranges were obtained by spreading the powder into the sintering die and consolidating them by sintering at 900°C and 1000°C for 30 minutes in vacuum (10-4 Torr). The metallic foams obtained by sintering hollow particles presents high porosity, and can be used as thermal barriers, catalyst support, shock absorbers or lightweight structural elements.

Abstract: Nanocrystalline nickel ferrite powder was obtained using high energy reactive ball milling technique. Nickel oxide (NiO) and iron oxide (Fe2O3) powders were used as starting material. Milling was performed in air atmosphere using a planetary ball mill. Milling time was up to 30 hours. The product of milling was annealed at 350 oC for 4 hours in order to eliminate the internal stresses and finish the solid state reaction. X-ray diffraction analysis was used to study the nickel ferrite formation. A nanocrystallite mean size of 10 nm was found after 24 hours of milling. Using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDX) the particle morphology and the chemical homogeneity were studied. It was found that the obtained product has particle size in range of micron and submicron.

Abstract: The nanocrystalline zinc ferrite (ZnFe2O4) powder was synthesized by high energy reactive ball milling (RM) in a planetary mill. As starting materials a mixture of commercial zinc oxide (ZnO) powder and iron oxide (Fe2O3) powder was used. The starting mixture was milled for different periods of time, up to 30 h. The milled powders were annealed for 4 h at 350 oC in order to eliminate the internal stress and to finish the solid state reaction of ferrite formation. Zinc ferrite formation was investigated by X-ray diffraction. The obtained powder has a mean crystallite size of 12 nm after 20 h of milling. Using scanning electron microscopy (SEM) the particle morphology was studied. Particles size range of the powders was also determined using a laser particle size analyser.