Papers by Keyword: Casting

Abstract: Advances in processes using the powder metallurgy techniques are making this technology competitive compared to the other traditional manufacturing processes, especially in medicine area. The additive rapid prototyping technique – selective laser melting (SLM) was applied in a biomaterial of CoCrMoFe alloy (ASTM F75), to study the mechanical properties and microstructural characterization in comparison between the conventional technique – casting. The gas atomized powder was investigated by their physical (as apparent density, bulk density and flow rate) and the chemical properties. The powder was analyzed using scanning electron microscope with energy-dispersed X-ray spectroscopy (SEM-EDS) and X-ray fluorescence. Specimens of standard samples were manufactured using these techniques to evaluate the mechanical properties as uniaxial tensile (yield strength, rupture tensile and elongation), transverse rupture strength and the micro hardness. The mechanical properties showed higher values in the SLM specimens than the casting specimens. Before the mechanical tests the specimens were examined using optical microscope (OM) and SEM-EDS. The micrographs revealed a microstructure with finer morphology in the SLM technique and the dendrites in the casting technique.

Abstract: The aim of this study is the consolidation of Cobalt-Chromium (CoCr) alloy powder using the additive manufacturing - selective laser melting (SLM) and the investment casting techniques. The research of this study has been applied to their biomaterial applied to development of prosthesis and dental implants. The gas atomized powder are spherical (mean diameter equal to 42,74 μm) and was analyzed by their physical and chemical properties. The microstructure of the powder and specimens was evaluated using optical microscope (OM) and scanning electron microscope with energy-dispersed X-ray spectroscopy (SEM-EDS). The mechanical properties were evaluated of standard samples using a tensile (yield strength, maximum tensile, rupture tensile and elongation), three point bending (transverse rupture strength) and micro hardness tests. The mechanical results indicate higher values for the SLM than casting specimens. The micrographs revealed a characteristic morphology of laser been used in the SLM technique and the dendrites in the casting technique. The microstructure of samples made by SLM is thinner than the samples obtained in the cast.

Abstract: It was difficult to prepare micro-hole with large aspect ratio by traditional processing technologies. In order to solve the problem, a preparation was proposed. It was carried out by casting method. Carbon fiber and metal wire coated graphite paint were used as hole core respectively. And morphology and geometrical characteristic of micro-hole were observed and analyzed by scanning electron microscope and laser scanning confocal microscope. The results showed that average diameter and aspect ratio of micro-hole obtained by the group of carbon fiber hole core were about 0.2 mm and above 1700, respectively. For the other group, about 0.5 mm and 700, respectively. The micro-hole obtained by the metal wire coated graphite paint hole core was more close to circle. Its shape factor was about 0.72. The roughness of micro-hole value obtained by carbon fiber hole core was close to 3.2 μm, smaller than that of the metal wire coated graphite paint.

Abstract: Permanent mould casting was used as the production technique to produce the metal matrix composites (MMCs) specimens. Thermal measurements during the casting process were recorded. Based on these data, solidification graphs were plotted to understand the solidification characteristics. Solidification analysis was performed by interpreting the parameters drawn from the solidification graphs. Parameters such as; nucleation primary alpha phase temperature, liquidus arrest temperature, eutectic growth temperature and solidification time were identified. The results showed that addition of titanium carbide particulates (TiCp) into the aluminium-11.8% silicon alloy (LM6) have affected various time and temperature parameters of its solidification properties. These in turn will have an influence on the mechanical property of the MMCs.

Abstract: The production technology for automotive foundry castings has developed significantly during the past decade. The production of cylinder hats with more and more complex designs could be rather challenging for core makers. Heating might cause the annealing of the core, thus, the buoyancy of the molten metal increases which might cause the movement of the core. The heat distortion of the cores was examined with a Hot Distortion Tester. A universal Instron 5982 device was used for bending, wedge penetration strength and cold and hot compression tests. The test bars were prepared with cold- and hot-box processes using DMPA (Dimethylpropyl-amine) under laboratory conditions. The tests showed that the decrease of the bending strength is proportional to the amount of additives. The compression test results showed that the test bars produced with cold-box compression have the lowest and the ones with furan resin mixtures have the highest compressive strength.

Abstract: Al-Si-Mg alloys are commonly employed for the production of automotive castings. In view of the recent stringent emissions standards and consequent engine downsizing, these components must withstand higher temperatures and stresses than in the past. In this regard, the heat treatable quaternary Al-Si-Cu-Mg alloys gained particular interest in recent years, due to their superior mechanical properties and higher thermal stability. The present research activity was addressed to evaluate the influence of cooling rate on microstructure and consequently on room temperature tensile and fatigue behaviour of the A354 and C355 alloys. Samples for mechanical tests were produced under controlled cooling rates, in order to induce different secondary dendrite arm spacing (SDAS) values, classified as fine (20-25μm) and coarse (50-70μm). The experimental results showed that the cooling rate strongly influences the type, size and morphology of intermetallic particles. The presence of coarse intermetallic phases, mostly Fe-based, observed in coarse SDAS specimens, was reported to strongly affect ultimate tensile strength (UTS), elongation to failure and fatigue strength of both the investigated alloys. A correlation between UTS and fatigue resistance was found, independent of microstructural coarseness.

Abstract: Microstructure, micro-hardness and wear properties of Aluminium-Zinc-Copper (Al-Zn-Cu) alloys of various chemical compositions are investigated. Stir casting process is used to prepare the various alloy compositions with permanent metallic mould. Six different alloy compositions were developed by varying Zn and Cu content in aluminium matrix. The wear and frictional properties were studied using Pin-on-Disc wear tester in dry sliding condition under normal atmosphere. The developed Al-Zn-Cu alloy has inter-metallic stable θ (CuAl2) phase in the inter-dendrite region and is due to the addition of Cu from 1 to 5 wt. % in 60Al-(40-x) Zn alloy. When the Cu composition increases up to 2 wt %, the corresponding hardness increases significantly and is due to the formation of Cu-rich θ phase and also due to the solid solution hardening of Cu in Al-Zn alloy matrix. But after 2 wt % Cu addition it is observed that the hardness increase is marginal. Wear rate (WR) and specific wear rate (SWR) were increases with increase of load and sliding velocity and decreases with Cu addition. Coefficient of friction (COF) remains constant for entire load and velocity for each alloy. However, when the alloys were tested at elevated temperatures, it was found that initially WR, SWR and COF decreases with temperature and then increases rapidly.

Abstract: In addition to conventionally casting, dental metallic framework can be manufactured using different CAD/CAM technologies (selective laser melting, milling). The milling of porous CoCr blanks followed by sintering under protective gas is a new 2012 introduced dental technology called Ceramill Sintron. For this new material so far, there exist few studies on the corrosion behavior. The aim of this study was to investigate the influence of different pH values as well as fluoride additions on the corrosion behavior of the sintered CoCr alloy compared to the cast condition by electrochemical corrosion measurements according to ISO 10271.

Abstract: As one of processing methods of functionally graded materials (FGMs), centrifugal mixed-powder method has been proposed. The centrifugal mixed-powder method is the casting process combined of centrifugal casting and powder metallurgy. This processing method has advantage that fine ceramics-particles, whose wettability with matrix melt is low, can be compounded into metallic material. However, effects of particle size on microstructure and mechanical properties of the FGMs fabricated by the centrifugal mixed-powder method are unclear. In this study, two kinds of Al-TiO₂ FGMs rings are fabricated by the centrifugal mixed-powder method. One contains TiO₂ particles having similar diameter with Al matrix particles (hereafter, small different-size (SD) TiO₂ particles), and the other one compounds TiO₂ particles with much smaller diameter than Al matrix particles (hereafter, large different-size (LD) TiO₂ particles). In case of the Al-TiO₂ FGMs ring containing SD-TiO₂ particles, the TiO₂ particles are homogeneously dispersed in Al matrix on outer surface of the ring. On the other hand, the TiO₂ particles in the Al-TiO₂ FGMs ring with LD-TiO₂ particles are distributed along grain boundary of Al matrix. Moreover, Vickers-hardness and wear resistance around outer surface of the Al-TiO₂ FGMs ring containing the SD-TiO₂ particles is higher than that of the Al-TiO₂ FGMs ring with LD-TiO₂ particles. Since Al particles in the mixed-powder with LD-TiO₂ particles are surrounded by the TiO₂ particles, the Al particles can be hardly melted by heat of molten Al at casting process. As a result, the Al-TiO₂ FGMs ring with LD-TiO₂ particles has low hardness and wear resistance. Therefore, it is found that TiO₂ particles having similar diameter with Al matrix particles are more suitable for fabrication of the Al-TiO₂ FGMs rings.

Abstract: Al-Li alloys have higher mechanical properties and more lightweight than other conventional aluminum alloys. Therefore , it is focused as a good material for weight reduction of industrial fields. However, since the Al-Li alloy are highly active and hard to cast, there has been limited research on casting. In this study, age-hardening behavior of Al-2.5mass%Li alloys cast into sand and metal mold were investigated. All alloys cast into Y-block shape sand mold, and then artificial aged after solution treated at 743K for 36ks. Because of difference in quantity of precipitation by metastable δ’(Al₃Li) phase, peak hardness of metal mold casting is higher than that of sand molds castings.