پژوهشنامه ریخته گری
سال پنجم شماره 2 (پیاپی 17، تابستان 1400)

In this study, the effects of Sb addition and casting modulus on the microstructure, morphology of graphite, and mechanical properties of ductile cast iron were investigated. For this purpose, a ductile cast iron with different casting modulus of 8, 15 and 30 mm were cast. Also, in order to examine the effect of Sb element in another mold with similar conditions, 0.01 wt% of Sb was added to the melt followed by the microstructure evaluation using an optical microscope. MIP4 image processing software was used to analyze the microstructure images. Brinell hardness and tensile tests were conducted to evaluate the mechanical properties. The results of this study showed that with increasing the casting modulus, nodule count decreased from 500 to 235 nodule per square mm, also nodularity decreased from 71 to 63%. In addition, the study of the results of hardness and the tensile test showed that with increasing the casting modulus, the hardness decreases from 289 to 212 HB and the yield strength from 430 to 350 MPa. Comparison of samples containing Sb and without Sb showed that Sb increased the nodularity, nodule count and volume fraction of perlite. For example, for the sample with 1 mm modulus, the presence of Sb increased the nodule count by 49%, improved the nodularity from 65% to 68.5%, and also increased the perlite volume fraction by almost 11%.

The aim of this study was to investigate the creep behaviour of GTD111 nickel base superalloy produced by directional solidification method. First, a cluster of cylinders of this alloy were cast by Bridgman method. Then, by preparing the tensile specimens, they were subjected to creep test at 870˚C and different stresses. Creep behaviour and microstructural changes of this alloy were measured and evaluated by various tests. Considering that the aim of this project is to identify the creep behaviour in the condition that the grains deviate from the ideal angle during directional solidification, first the grain structure was determined in casting samples, then their mechanical behaviour was investigated by determining the grain deviation. Also, numerical simulation was used to model the grain size of the cast samples. By three-dimensional modelling of grains in creep specimens and then changing the growth angle of dendrites in each grain, numerical analysis of the creep of the specimen using Norton equation and changes in creep life by changing the deflection angle of the grains was obtained. The results showed that increasing the angle of deviation during the growth in a grain from zero to 3 degrees caused a 0.4% increase in mean stress and increasing the growth angle in the same grain from 3 to 10 degrees, caused a 5% increase and an increase from 10 to 20 degrees caused an 11% increase in mean stress in this grain in the middle section of the sample.

In this study, the effect of melt holding times for 15, 30, and 45 minutes at superheating temperatures of 200, 250, and 300 °C on the phase of Mg2SiP, eutectic Mg2SiE, Al5FeSi, Al5Mg8Si6Cu2, Al2Cu, nucleation temperature of these phases, and the hardness of Al-20Mg2Si-2Cu composite were examined. Microstructural observations and quantitative analysis showed that the best modification was achieved at superheating of 300 ° C and a holding time of 15 minutes. Compared with the reference sample with 100 ° C superheating, the dendritic and coarse morphology of Mg2SiP particles changed to the fine polyhedral. The average particle size decreased dramatically from 1179 to 255.5 μm. Particle area and aspect ratio decreased by 83% and 13%, respectively. The number of particles per unit area increased from 9 to 57. Superheating converted the needle β-Fe to the β α-Fe Chinese script, although no significant change in the features of the Mg2SiE, Al5Mg8Si6Cu2, and Al2Cu phases was observed. A good correlation was found between the nucleation temperature and the microstructural transformation of the Mg2SiP phase. After implementing superheating of 300 °C for 15 minutes, the nucleation temperature of the Mg2SiP phase increased from 647.3 to 664.4 °C. The superheating treated composites showed higher hardness than the reference specimen, regardless of temperature and time. The highest hardness was obtained with 82.1 Vickers, which could be attributed to increasing the number of particles and reducing the distance between particles.

Melting furnace charge calculation is often performed based on the mass balance of alloying elements between input materials and output melt. However, real melting processes are concerned with phenomena and complexities, which are ignored in simplified mass balance calculations. That causes uncertainty in the charge calculations, which further leads to multiple melt corrections, delays in tapping, cost raises, and melt quality problems. This study aimed to develop a model that not only optimizes charge materials for a specified target melt, but also considers non-homogeneous element loss, non-metal contaminations in charges, and correction of initial melt in the furnace. This paper proposes a standard optimization approach with an iterative algorithm for non-linear mass balance in the melting problem. A test case was introduced to find charge materials for target brass alloy C47940 in a 10-ton induction furnace, with an initial 7-ton out-of-range melt. The matrix of coefficients was built according to the numerical algorithm of the model. The results of the test case showed the optimum mass fractions of charge burdens. An optimality analysis was conducted and showed that the solution has reached the minimum possible cost. The non-linear iterative algorithm revealed a convergent and fast performance which has potential for reliable optimization in melting operations with significant benefit for industrial automation.

Using a high quality, clean melt is a fundamental prerequisite for production of high-quality Al castings. So far, a variety of techniques have been suggested to increase the quality of cast Al alloys including, rotary degassing and the use of fluxes and ceramic foam filters during melt preparation and casting. While the dissolved hydrogen in molten Al alloys is considered as the main cause of the formation of pores and therefore, the low quality of cast aluminum alloys, the study of the literature in this paper demonstrates that hydrogen itself has almost no negative impact on the quality of these alloys. The present paper suggests that the sole factor that impairs their quality is the presence of oxide films and inclusions. Also, this paper suggests a practical procedure to evaluate the damages to cast Al alloys during the production steps that is based on the reduced pressure test and uniaxial tensile test.

The investment casting process is a reliable way to produce complex and delicate shapes , with good surface quality and high dimensional accuracy. The main advantage of investment casting is the ability to produce a wide variety of products from different industries, and non-machinable components can be cast in the same predetermined way, so that the final component generally does not need to be welded and assembled, thus saving time and money. This method was used in ancient times to produce weapons, jewelry and artistic sculptures. Over the centuries, this technology has advanced and is used in the casting of various works of art, industrial parts and the production of turbine blades. The present article is an overview of the application of investment casting process in the production of artistic pieces. In this article, investment casting history, model wax properties, adhesives, additives and fillers, ceramic shell fabrication process for non-ferrous alloys, comparison of microwave and autoclave dewaxing methods, smelting and final operations, 3D printing method for Model construction and finally the simulations used to predict defects and model optimization will be reviewed separately.