Kahraman, Ece
Powder bed additive manufacturing methods use the powder form of the material of the part to be produced as raw material. The quality of the production is highly dependent on the properties of the powder used in the first place. Consistently using new unused powder for each new additive manufacturing is costly and removes the advantage of additive manufacturing, i.e. low amount of waste material. In powder bed additive manufacturing methods, powders are laid layer by layer and melted by laser or electron beam to form the final piece. Since the areas determined according to the CAD data of the part in each layer are scanned and melted, the surrounding powders remain unmelted and at the end of the production, the part is cleaned from the remaining powders. Bringing these remained powders back into another production is cost-effective. However, it is important not to compromise on the quality of the parts. Therefore, it is necessary to investigate the effects of reusing metal powders on additive manufacturing parts. In this thesis, the effects of powder reuse on the properties of selective laser melted 17-4 PH stainless steel were investigated. Using the same powder, 10 successive productions were carried out. In the productions, it is aimed to increase the thermal history of the powders as much as possible by producing geometries in a way that the powders will be most affected by the laser. Samples were taken from the powders in accordance with the standards before the first production and after the last production. These samples were subjected to various tests such as shape analysis, dimensional analysis and chemical composition analysis. In addition, block parts and tensile test specimens were produced in order to examine the part properties in certain productions. As a result of reuse of the powders 10 times, no change was observed in the powder shapes, bulk densities, particle size distribution and mechanical properties of the obtained parts. However, the tapped density value of the reused powder increased by 7.7% compared to the unused powder. In addition, it was determined that the oxygen ratio increased by 16% and the nitrogen ratio increased by 17% in reused powders. It is evaluated that with the further increase of the reuse cycle of the powder, the powders will become more contaminated and the raw material will go out of specification.


The Optimization of Dilute Acid Hydrolysis of Cotton Stalk in Xylose Production
AKPINAR, ÖZLEM; Levent, Okan; Bostanci, Seyda; Bakir, Ufuk; Yılmaz, Levent (Springer Science and Business Media LLC, 2011-01-01)
Cotton stalk, a lignocellulosic waste material, is composed of xylose that can be used as a raw material for production of xylitol, a high-value product. There is a growing interest in the use of lignocellulosic wastes for conversion into various chemicals because of their low cost and the fact that they are renewable and abundant. The objective of the study was to determine the effects of H(2)SO(4) concentration, temperature, and reaction time on the production of sugars (xylose, glucose, and arabinose) an...
Characterization of Ti-6Al-4V alloy foams synthesized by space holder technique
ESEN, ZİYA; Bor, Sakir (2011-03-25)
Ti-6Al-4V foams, biomedical candidate materials, were synthesized by powder metallurgical space holder technique as a result of evaporation of magnesium to achieve desired porosity content. Final products contained porosities in the range similar to 43-64% with an average macropore size between 485 and 572 mu m and a lamellar type Widmanstatten microstructure composed of alpha-platelets and beta-laths. Unlike the case of bulk Ti-6Al-4V alloy tested under compression loading, compression stress-strain curves...
An investigation on use of colemanite powder as abrasive in abrasive waterjet cutting (AWJC)
Cosansu, Gulay; Cogun, Can (2012-08-01)
In the present study, the cutting performance outputs (surface roughness, surface waviness and kerf taper angle) of colemanite powder as abrasive in abrasive watedet cutting (AWJC) with varying traverse rate and abrasive flow rate were investigated experimentally. The performance outputs were compared to that of garnet which is in common use in industry as abrasive in AWJC industry. A17075, marble, glass, Ti6Al4V and a composite material were selected as sample materials in the experiments. Furthermore, col...
The performance of polyethersulfone nanocomposite membrane in the removal of industrial dyes
Mahmoudian, Mehdi; Ghasemıkouchameshgı, Mahmoud (2021-05-14)
In the present study, graphene oxide was functionalized by hyperbranched epoxy and then used as an additive in the polyethersulfone membrane. The process of preparation and characterization of the synthesized hyperbranched epoxy, and graphene oxide modification was investigated by some analysis such as XRD, EDAX, FTIR, NMR, and TGA. Morphology of modified nanostructures, their distribution in the membrane matrix, and morphology of membranes were evaluated by TEM, FESEM analysis. Experimental results showed ...
The formation of smooth, defect-free, stoichiometric silicon carbide films from a polymeric precursor
Pitcher, Michael; Bianconi, Patricia (2006-04-20)
Silicon carbide (SiC) materials, which are used in a variety of applications, are often produced using powder processing, sintering or bulk crystal growing techniques. The formation of silicon carbide films or shaped products, via these methods, is often extremely difficult and/or requires high temperatures. Here we report the synthesis and characterization of a polymeric precursor, Polymethylsilyne (PMSy), and it subsequent conversion to beta-SiC. The polymer is simple to synthesize and is easily manipulat...
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