نشریه ریخته گری
پیاپی 102 (تابستان 1392)

IN-713C nickel-base super alloy is being widely used in manufacturing of gas turbine blades and turbocharger impellers due to its high temperature strength and oxidation resistance.Vacuum melting and casting is the standard method for manufacturing components out of the alloy. The as cast microstructure of the alloy has been shown to have significant effects on the castings mechanical properties at high temperatures.In this research the microstructural characteristics of the vacuum investment cast alloy was studied by scanning electron microscopy, energy dispersive spectroscopy and image analysis techniques.Creep tests were performed according to ASTM E-139 standard to evaluate the mechanical properties.The results showed that the microstructure consisted ofγdendrites, primary and eutectic carbides and coherent γ’ precipitates. Type, morphology, volume fraction and composition of carbides and γ’ precipitates as well as dendrite arm spacing were investigated to provide desirable microstructure for passing the standard mechanical tests. Presence of 55 vol.% γ’ precipitates with cubic morphology and 540nm dimension as well as 10 vol.%carbide in the microstructure was found to be necessary for satisfying the standard creep test requirements.

Aluminum foils have found wide applications in various industries such as food packaging and pharmaceutical industries due to their exclusive properties. One of special applications is aluminum foil packaging for food and drug due to its excellent protection against environmental influences. According to the gradual thickness shrinking of the aluminum sheet in rolling process, it is possible to create the defects in the manufacturing process that is the most important disadvantage of the micro ruptures in the sheet and foil. Micro rupture is a metallurgical flaw that appears in the thickness under 180 micrometers; however, this defect is not acceptable in critical applications such as diagnostics industries listed and limits the foil application. In present study, sheet samples of aluminum foil 8011with thickness of 11 to 200 μm were collected. To study the microstructure of aluminum sheet and foil, a Scanning Electron Microscope with EDS analysis was used. The results of the study indicates that metallurgical factors in the emergence of micro ruptures in sheet level are related to the sheet aluminum volume loss due to factors such as segregation and voids caused by the detachment of intermetallic brittle compounds.

Casting is one of the processes for producing bimetals which has various advantages over other processes. In this process the melt of one metal/alloy is poured around a solid component of other alloy inserted in the mold. In this work the Al melt was poured in two melt/solid ratios (3 and 5) in 700 and 750 Celsius around a brass rod. Macroscopic studies showed that a solved ring is formed around the solid core which is clearly visible after cutting the casting. XRD, optical microscopy and SEM studies showed that various layers can be distinguished which are CuZn, Al4Cu3Zn, Al2Cu, eutectic of α-Al/Al2Cuand finalyAl dendrite eutectic in the vicinity of Al melt. Hardness of the layers was 513, 477 and 650 Vickers respectively, from brass core to aluminum side. In the 700 Celsius pouring temperature less pores and more homogeneity in the phaseswere noticeable.

Precise appraisal of products and submission of suitable reports for decision-making is the goal of a costing system. Therefore, one of the concerns of steel industry is providing finished price to remove the weaknesses of absorptive costing system and providing proper information to access an integral quality. In fact, this system is one of the powerful and suitable tools for companies to access their goals and to preserve their competitive power. This paper studies the effective factors for a feasibility study for implementation of an activity-based costing system (ABCS) in alloy steel industries of Iran. The factors that deviate finished price in absorptive costing are: high production overload, production complexities, production diverse, volume diverse, production physical size diverse, complexity of raw materials, high inventory of finished semi-finished products at the end of period, and recognition of cost storages and cost-creation factors. Survey method was used to gather data including library, interview, and questionnaire. T Test was used to confirm or reject the assumptions. It was found that implementation of an activity-based costing system is feasible in ASI.

Because of the excellent performance of ductile irons and the unique superiority of investment casting, the preparation of complicated and thin-wall ductile iron castings by investment casting prospect. According to some experiences in Poolad Foam Pouya CO. the production of ductile irons by investment casting process show complicate problems such as ceramic layer broken, inclusion entrapment, abnormal microstructure and so . This article give some suggestions to prevent the problems.

Unique electrical, mechanical and thermal properties with a low density of carbon nanotubes makes a good candidate for use in the reinforcement of composites and are raised to attract the attention of many researchers. In this study, mixtures of aluminum powder with various amounts carbon nanotube (from zero to 3 weight percent) is produced and milled by planetary milling .In order to dense and strength of milled powder cold isostatic pressing and sintering are used. The samples were tested by micro hardness. The results obtained show that addition of 2 weight percent carbon nanotube has maximum micro hardness and are 4 time of the pure milled aluminum.

In this research a model was investigated for nucleation and growth that can simulate solidification microstructure in various solid fraction. By fluid flow simulation, velocity and pressure contour in Re=0.1 was calculated. Simulations data and Darcy’s law was used to calculate permeability for more than 250 case and used them to educate neutral network. Solidification of dumbbell like part was simulated completely and by using solidification process data as cooling rate and solid fraction with educated neutral network, permeability in solidification process for macro part calculated and used for prediction of micro/macro shrinkages location that compared with PROCAST software results. In attention to simplicity of selected part, simulated location for porosities shows best accordance to predictable locations.

Dendrite coherency point (DCP) is one of the most important characteristics in solidification process of alloys. Impingement of growing dendrites and adjacent dendrites is occurred at this point. Coherency between dendrites changes the melt feeding condition from mass feeding to inter-dendritic feeding. As dendrites skeleton network is formed at this point, flow of melt becomes more difficult in all sections of the casting and this event leads to increase in thermal stresses. Thermal stresses originated from contraction during solidification process causes some imperfections in castings such as, micro- and macro-segregation, shrinkage and gas porosities, and hot tearing.
Therefore, determination of DCP can be useful to prevent these imperfections. In this investigation, two thermocouples computer-aided thermal analysis method was used to detect the effects of time and temperature in the formation of dendrite coherency point. 2024 aluminum alloy was melted and processed at two conditions; without grain refinement and grain refined with 1.2 wt.% Al-5Ti-1B master alloy. The effect of grain refinement on the time of dendrite coherency and solid fraction in DCP is presented in this paper.