Abstract: Fe/Fe2O3 composite powders were obtained by mechanical milling of iron and hematite up to 120 minutes in a high energy planetary ball mill. The particles size decreases by mechanical milling upon the formation of the Fe/Fe2O3 composite particles. After 120 minutes of milling the median particles size is at 7.2 μm. The Fe/Fe3O4 type composite were obtained by reactive sintering in argon atmosphere at 1100 °C of the Fe/Fe2O3 composite powders milled for 60 and 120 minutes. After sintering a FeO-wüstite residual phase is formed and this phase is eliminated by applying a subsequent annealing at a temperature of 550 °C. The sintered compact before and after annealing is composed by a quasi-continuous iron matrix in which are embedded iron oxides clusters (Fe3O4 and FeO before annealing and Fe3O4 after annealing). The iron oxide clusters are analogous with the Widmanstatten structure observed in steels before and after annealing. The materials have been investigated using laser particle size analysis, optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction.
Abstract: Nanocrystalline/nanosized magnetite - Fe3O4 powder was obtained by mechanical milling of well crystallized magnetite obtained by ceramic method starting from stoichiometric mixture of commercial hematite - Fe2O3 and iron - Fe powders. The mean crystallites size of the magnetite is decreasing upon increasing the milling time down to 6 nm after 240 minutes of milling. After 30 minutes of milling an undesired hematite phase is formed in the material. The amount of this phase increases upon increasing the milling time. In the early stage of milling (up to 30 minutes) the existence of nanometric particles (mean size below 100 nm) is noticed. The d50 median diameter decreases first (up to 5 minutes of milling) and after that, an increase follows for milling times up to 120 minutes. Saturation magnetization decreases upon increasing the milling time and is more difficult to saturate. X-ray diffraction, laser particle size analysis and magnetic measurements have been used for powder characterization.
Abstract: Natural fibers have recently become attractive to automotive industry as an alternative reinforcement for glass fiber reinforced thermoplastics. The best way to increase the fuel efficiency without sacrificing safety is to employ fiber reinforced composite materials in the body of the cars so that weight reduction can be achieved. The latest thermo plastic developments have resulted in higher material properties and more possibilities in the design of bumper beams. However the use of steel, aluminum, glass thermoplastics, sheet metal components, bumpers becomes at higher cost than long fiber reinforced thermoplastics.
Abstract: The paper presents the influence of various cutting regimes on the surface roughness, when a hardened bearing steel has been machined using both ceramic and PCBN cutting tools. There were used different cutting conditions varying cutting speed, feed rate and depth of cut in order to determine the influence of each cutting parameter on the surface finish.
Abstract: The paper aims to provide an insight into the thermo-physical changes of in-situ tailored hybrid polymer based composite materials based on two different synthetic reinforcements with the aim of sizing both architecture stacking sequences and reinforcement type’s influence on their effective linear coefficient of thermal dilatation (CTE). The samples were subjected to a step ramp temperature increase up to 250 °C, followed by their CTE variation monitoring and assessment. Data processing and comparison further contribute to expand knowledge and appropriate personal database aiming material design, manufacturing error minimization and cost reduction.
Abstract: In the paper is presented the study of the Fe2O3 powders granulation effect on the firing parameters for the BaCO3+6Fe2O3 powder mixture. The Fe2O3 powders were milled in a ball mill in wet medium. The results indicated that the granulation of Fe2O3 powders decreased rapidly with the increase of milling time. The Fe2O3 milled powders were then mixed with unmilled barium carbonate powders in order to form barium hexaferrite. After mixing, the powders were analized by thermogravimetric point of view and then the obtained barium hexaferrite samples were investigated by XRD analysis. It was observed that the firing temperature of the hexaferrites decreases with 10 degrees when we introduce in the mixture Fe2O3 milled powders with a fine granulation.
Abstract: Result of research concerning the influence of milling conditions on the amorphisation of the Fe75Si20B5 (at.%) alloy is presented. Amorphous powder of Fe75Si20B5 (at.%) was prepared by dry and wet mechanical alloying (MA) route starting from a mixture of Fe, Si and B elemental powders. The mixture was wet/dry milled up to 50 hours. Benzene, oleic acid and ethanol were used as process control agents (PCA) in order to investigate the influence of their chemical composition on the powder amorphisation. The evolution of the powder crystalline structure, thermal stability and magnetic properties were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG) as well as magnetic measurements versus temperature and field. It is proved that the chemical composition of the PCA (especially the carbon content) plays an important role in the amorphisation process induced by wet MA.
Abstract: Using powder metallurgy techniques new porous materials for self-lubricating bearings were developed. These materials are characterized by total porosity, which represents their major advantage for tribological applications, acting like their own oil reservoir. Sometimes the presence of pores can be also detrimental to the part performance. Among the causes of the bearings failure is their increased porosity for improving the lubricant retention capacity. Consequently, this can lead to a significant loss in strength. In the present work tensile test specimens based on Fe-Cu/brass-Sn-Pb powders were prepared in order to investigate the morphology of the fracture surfaces and to analyze the effect of pores on the failure process of these materials subjected to tensile loads. Distinct morphologies of the pores area were revealed by SEM images of the fracture surfaces.
Abstract: The evolution of the Al2O3/Ni (25% vol. Ni) composite powders, during the milling and the stability of the composite phases were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray microanalysis (EDX). SEM images show a high level of homogenization of the Ni and Al2O3 phases for milling times larger than 120 minutes. The X-ray study indicates no reaction between the two phases. The crystallite grain size decreases with the milling time for both phases.