Researches in Powder Metallurgy

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Authors: Mehmet Turker, Yusuf Ozcatalbas, Hanifi Cinici, Ugur Gokmen, Arif Uzun
Abstract: In this study various amounts of foaming agent (TiH2 % 0,5-1-1,5-2 ) were added to Al and Alumix 231 powders (Al-Cu %2,5-Mg %0,5–Si %14) and mixed for 30 minutes in a three dimensional turbula. Mixed powders were compacted and then foamed freely at 690°C. Effect of foaming agent on the structure, shape and distribution of pores together with linear expansion, density of the foam and wall thickness of the cell of both materials were investigated. In all conditions foam produced from Alumix 231 powders had more homogenous distribution of the pore compare to the sample produced from pure Al powders.
Authors: Catalin Popa, Viorica Simon, Gabriel Batin, Codruta Pavel, Ionuţ Gligor, Liana Conţ, Viorel Cândea
Abstract: Although titanium is considered to be the most successful metal for uncemented endosseous implants, its biocompatibility may be unsatisfactory in certain clinical cases. As an early osseointegration is essential in order to reduce the implant failure risk, the bioactive fixation becomes the appropriate solution for bone applications. The method requires bioactive materials such as hydroxyapatite (HA) to facilitate the chemical bonding to tissue. The present work refers to Ti-HA composites designed for endosseous implants and obtained through the classic PM route. Grade 1 c.p. Ti powder obtained through the hydriding – milling – dehydriding process, 63 - 100 μm grain size, was used. Sol-gel HA powder, grain size of less than 100 μm, was obtained through the sol-gel method. Blends of Ti and 5 to 50% HA were compacted in a rigid die (0.5 cm2), without the use of any lubricant, with 400, 500 and 600 MPa, then vacuum sintered (10-6 torr) at 1160°C for 60 minutes. Samples are well sintered with a compactness that increases with the applied compaction pressure. A transition layer can be seen in the EDX at the interface between the Ti matrix and the HA particles and is expected to increase the overall mechanical stability of compacts. The pores, essential for osseointegration, are interconnected, with irregular shapes and sizes that reach 100 μm, the critical size needed for the formation of a vital new bone. The HA content has to be limited to 30%, not to lead to an excessive brittleness. The biologic viability of compacts was assessed by immersion for 7 days into a simulated body fluid (SBF). The subsequent XRD analyses have proven that a new HA layer is formed on the surface of samples. This layer is essential for accelerating the cellular response of osteoblasts in the body.
Authors: Cristina Teișanu, Stefan Gheorghe
Abstract: In this study the formation of the liquid phase during sintering process of Fe-Cu-Sn-Pb system was investigated. In order to reach this purpose a new material based on iron powder was developed using PM technologies. Additions like copper, tin and lead were added to iron powder and the mixture was sintered in dry hydrogen atmosphere at different temperatures and maintaining time. The liquid phase formed during sintering led to a considerable accurate process and swelling of the sintered compact was observed and studied.
Authors: Cristina Ileana Pascu, Alexandru Stanimir, Ioan Vida-Simiti
Abstract: The paper presents the results of the experimental research carried out in order to obtain pseudoalloys WNiCu used in electrical industry, for the electrical apparatus of high tension and great power. As a result it was compulsory to study the parameters that influence the densification process and the sintered properties, depending on the grain-size distribution of tungsten powder, compaction pressure and sintering temperature in vacuum. Therefore, it has been studied the influence of these parameters on the density, hardness and microstructures changes for the composites with 78%W-2%Ni-20%Cu, (% wt). The better results were obtained for the value of 1350 0C for the copper infiltration temperature.
Authors: Liviu Brânduşan
Abstract: The behaviour of alloyed and unalloyed sintered steels in static and dynamic loading is influenced by their macro and microstructure. The characteristics of the used powder, their chemical composition, the conditions of shaping by pressing, and the parameters of the sintering process are some factors determining the structure of the steels [1, 2]. Under the same technological conditions, sintered materials were produced using iron powder of different particle size or in different powder mixtures for establishing the structure influence on some mechanical properties, The results obtained shows that the sintered materials present a higher sensitivity towards the dynamic and variable loads [2]. In the same time, it was shown that a material made from a fine powder fraction behaves, at mechanical loads, almost in the same way as an elaborated material from the same powder but with a wider particle size distribution or particles size. Using of the different powder mixtures lead to some microstructures with better mechanical properties at the intergranulars necks. Using the copper powder or the low or high alloyed iron powder in a mixture with the basic iron powder determines an improvement of the mechanical properties by changing the materials microstructure. It was found that the addition of high alloyed steel powder has the strongest effect on the fatigue resistance.
Authors: Mustafa Günay, Ulvi Şeker
Abstract: MMCs components are mostly produced using near net shape manufacturing methods and are subsequently machined to the final dimensions and surface finishes. The MMCs consist of extremely hard reinforcing particles and pose considerable challenges due to the poor machinability and severe wear of the cutting tool. In this study, cutting performance of WC, CBN and PCD cutting tools were investigated with respect to surface roughness during machining of 10 wt % SiCp reinforced Al-Si alloy matrix composites produced by powder metallurgy (PM) method. Average surface roughness (Ra) corresponding to each machining condition was measured. After the machining process the worn insert tips were examined under the scanning electron microscope (SEM). Chip geometry and machined surface photographs have been taken by optical microscopy. The experimental results showed that surface roughness decreased with increasing cutting speed for all of cutting tool materials. The best surface integrity was occurred after the machining with PCD insert at the highest cutting speed employed.
Authors: Victor Horia Nicoară, Iulian Ştefan
Abstract: In this work there are presented the results of experimental researches which had the goal to establish the thermal effect of BaCO3 and α- Fe2O3 homogeneity mixture heated in microwave, used to processing barium ferrite W type by pyrosynthesis.There was used thermal-gravimetric analysis with a derivatograph reordered for microwave heating of samples containing iron oxides with different grain size.Experimental results emphasized that the microwave heating comparatively with resistor heating, lead to a lower synthesis temperature of hexaferrite of about 150 0 C , using oxides with grain size suitable to SBET= (7-10) m2/g.
Authors: Marin Didu, Lucian Gheorghe Gruionu, Stefan Radu, Christian Ghermec
Abstract: The paper presents the results of the experiment in the fields of new technologies of obtaining PM reinforced with metallic yarns pieces. This type of high resistance porous pieces are made from a base part from recovered low alloyed steel or iron powder reinforced in the border zone with high alloyed steel yarns. For the reinforcing have been used solid yarns Φ 0,3 mm and mixed yarns Φ 0,45 mm. There have been obtained parallelipipedic samples reinforced with four yarns placed as in fig.1.1. The samples have been pressed at 300-600 MPa pressure. The pressing has been made orthogonal onto the placement direction of the yarns. The compacting has been made in an unidirectional compression mould with section of 7x51mm. The sintering was made at 1200 degree Celsius in an argon medium. The sintered samples have densities of 5,72g/cm3 (pressed at 300MPa) and 6,72 g/cm3 (pressed at 600MPa). There have been made mechanical bending tests. There were obtained bending strengths σi=490…800 MPa. From the things previously presented it can be observed that this type of reinforced with yarns pieces have high bending strength, though they have high porosity (low density).
Authors: Luisa N. Mîtcă, Radu Liviu Orban, Adem Kurt, Liviu Brânduşan, Nicolaie Jumate
Abstract: The possibilities of Cu-Al2O3 particulate reinforced composites, of competitive functional properties, processing by the classical powder metallurgy route have been investigated taking into consideration its known technical and economical advantages in respect to the known worldwide investigated technological routes of their processing. The adopted compositions, of (5.0÷20.0) [vol.%] Al2O3, were selected in agreement with published data for a large range of applications. Pharmaceutical homogenization method applied for powder mixtures preparation proved to assure a high homogeneity, evidenced by SEM and EDS analyses. Their determined compressibility has shown that, for all compositions, the obtainable compactness is very close to that of pure Cu (even over 94 %). Cold uniaxial compaction at 500 and 700 MPa, and subsequent sintering in argon of high purity at 800 °C for 45 and 60 min have been adopted for composites realization. The performed analysis of the compacting pressure and sintering time influence on the composite compactness proved that, beside the above specified values obtaining for 700 MPa and 60 minute processing parameters, high enough values, acceptable for numerous applications, can be also obtained at 500 MPa and 60 or even 45 minutes. Finally, microstructural analysis highlighted that, by the adopted processing conditions, a high uniformity of Al2O3 particles distribution in the Cu matrix can been assured, both creating premises for obtaining good functional properties of Cu-Al2O3 composites, proving the competitiveness of the investigated PM route for their elaboration.

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