Materials and Technologies

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Authors: Virgiliu Călin Prică, George Arghir
Abstract: Fe-Cu system is a binary alloys system, nevertheless very difficult. This paper presented the milling duration influence on ball-milled Fe30Cu70 alloys. After 16 hour of milling it has been concluded that true alloying at atomic level occurs during milling. The average grain size depends by milling time. Varying the milling time changes the powder morphology, their size and structure. We found that the complete fcc Fe –Cu solid solution is formed when the grain size of Fe-bcc reach a value about 10 nm, because at this value of crystallite the free energy for interface become less than interfaces energy. The milling duration have a strongly influence on solid solubility and phases form in Fe-Cu system. The phase formation for Fe30Cu70 (mass %) has been investigated by X-ray diffraction (XRD). The mixing enthalpy (positive in this system) also depends on alloy composition.
Authors: Mariana Lucaci, Radu L. Orban, Delia Patroi, S. Hodorogea, I. Bibicu, Magdalena Lungu
Abstract: Research results focussed on the combined influence of iron and boron, in proportions of 0.5 and up to 10 wt.% respectively, in complex alloyed Ni3Al synthesised by Self Propagating High Temperature Synthesis (SHS) in the thermo-explosion mode at two ignition temperatures, 950 and 1150 oC, are presented. By XRD and Mössbauer spectroscopy it was established that for 950 oC ignition temperature, the evolved heat is not high enough for the added Fe to be fully incorporated into the synthesised Ni3Al phase, a temperature of 1150 oC being required. For this temperature, the density of the synthesised alloys, their capacity to be cold deformed by re-pressing, hardness and bending strength variations as a function of B and Fe contents, proved their cumulative effects of the ductility and mechanical properties of complex alloyed Ni3Al enhancing.
Authors: R. Yilmaz, A. Gökçe, Hakan Kapdibaş
Abstract: In this study, various ratios of ferro-molybdenum were added into low alloy distaloy steel powder and then the compacts were fabricated by powder metallurgy process. The effect of ferromolybdenum addition on the properties of these sintered materials such as density, microhardness and impact toughness were investigated. The results obtained from experimental works showed that ferro-molybdenum addition to the starting powder resulted in an increment in density and microhardness values. On the other hand, ferro-molybdenum addition has influence on impact toughness values of the sintered low alloy steel.
Authors: L. Adriana Sorcoi
Abstract: This paper presents Cu90Ni10 alloy properties. These alloys were produced in three distinct modes: alloyed powders (P), powder made from elemental powders of copper and nickel (A); powders from the Cu80Ni20 alloy and an alloying element (D). The influence of time, composition and properties of the powder mixture upon the final properties of the sintered alloys was studied. A comparative study of the sintered compacts obtained by varying the parameters of procedure, compacting pressure and sintering time was performed. The work aimed to research the influence of the parameters above mentioned: density, compressibility, structure of compacts, etc. The sintering capacity was also assessed through the resistence to fracture and hardness of samples, also versus the parameters above mentioned.
Authors: R. Ivănuş, Liviu Brânduşan
Abstract: Powders-based on the Fe-Cu-Ni-Mo system are well known in the P/M industry for combining good compressibility and dimensional stability with a potential for high strength. The typical heterogeneous microstructure of these materials has proven to provide favourable mechanical properties. However, in applications where strength and hardness become critical variables, faster cooling rates after sintering are required to meet application requirements. Test specimens containing various graphite contents to achieve 0.20, 0.35 and 0.55% combined carbon were pressed to 7.0 and 7.2 g/cm3, sintered in a furnace at 1150°C and cooled directly from sintering temperature with either normal or rapid cooling. Test results are discussed in terms of tensile properties, apparent hardness and microstructure. The formation of bainite and martensite by raising carbon content and cooling rate increased tensile strength and apparent hardness, while a higher green density maintained satisfactory ductility. It was possible to achieve ultimate tensile and yield strengths as 920 and 660 MPa respectively with apparent hardness 30 HRC.
Authors: Dana Salomie, Codruta Pavel, Radu Mureşan
Abstract: The main objective of this study is to find out a simple method to ensure a good dispersion of Al2O3 in the Cu matrix. The method should avoid the segregation effect due to the high difference of the densities of Cu (8.93 g/cm3) and Al2O3 (3.96 g/cm3). In the process of obtaining of the Cu-Al2O3 composite we have considered starting with a material whose density is closer to the density of Al2O3. We have chosen CuO whose density is about 6 g/cm3 so the composite material was obtained starting with copper oxide and alumina powder. We have studied the influence of Al2O3 content and of the compacting pressure upon material’s compactness and hardness. The dispersion finer is highlighted by the microstructure of the surfaces.
Authors: Zeno Spârchez
Abstract: The conditions needed for an efficient separation together with the most important factors influencing the accuracy of the separation are emphasized. Some relationships that allow the evaluation of the covering degree of the separation surface and the volume of the charge with single dimension particles corresponding to a unit separation surface are presented. The efficiency of spherical shape particles separation and the productivity of the separation process have been analysed. Some technical and practical considerations on the separation process are given.
Authors: Zeno Spârchez
Abstract: The paper describes the working principles for six types of separation devices mentioned in the literature, as well as two original types of separation devices devised by the author. In fact the functionality of each device presented in the paper is based on the difference between the friction coefficients – sliding friction for non-spherical particles and rolling friction for spherical ones, respectively. Due to this peculiarity, the two types of particles move along different trajectories, thus becoming separable. The paper also discusses the limit conditions ensuring the functionality of each separation device.
Authors: Zeno Spârchez
Abstract: On the basis of a graphical classification devised by the author, the paper presents a brief analysis of the principal methods and procedures used for elaborating powders having spherical particles. The than discussion is focused on emphasizing and classifying the influence factors related to the material, processing method and equipment, which enables the obtaining of spherical particles. In the case of those methods which lead to both spherical and non-spherical particles, additional operations are needed the separation of the non-spherical particles, possibly followed by their conversion to spherical particles in a thermal field.
Authors: D.A. Pop, George Arghir
Abstract: During ball milling of ductile-brittle systems, often is reported a massive coating of milling devices (balls and walls of the vials). Therefore, to slow the powder deposit on the milling devices, it is useful to analyze the causes that initiate and favour the phenomenon. It seems that the massive powder coating of milling devices is very similar to build-up edging of the materials on the cutting tools in machining. The aim of the paper is to find what differences appear in the coating when are used different powder compozitions, or compozitions with fractions of powder previously milled compared to initialy unmilled compozitions.

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