Investigation of Thermal Parameters Effects on the Microstructure, Microhardness and Microsegregation of Cu-Sn alloy Directionally Solidified under Transient Heat Flow Conditions (original) (raw)
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Materials Research
Hypoperitectic Cu − 20 wt.% Sn alloy was solidified under different cooling rates and solidification growths using directional solidification system. The effects of cooling rate and solidification growth on the microsegregation profiles and tertiary dendritic arm spacing (λ 3) were experimentally investigated along the casting. A mathematical model known as phase-field was applied to simulate microstructure and microsegregation during solidification in system Cu-Sn liquid. In this paper the applicability of the phase-field model to the solidification problem in a real alloy system was systematically explored. Microsegregation profiles and realistic dendritic structures were obtained using the phase-field model. The results calculated by phase-field model show various solidification features consistent with our experiment. The calculated tertiary dendritic arm spacing (λ 3) and microsegregation profiles were compared with experimental values from directional solidification system. Since the calculated microsegregation profiles using the equilibrium partition coefficient (k eq) can yielded discrepancies from the experimental results, an effective partition coefficient (k ef) as a function of solidification growth, is proposed in phase-field model, showing a good agreement with the experimental data for any case examined.
Advances in the Science and Engineering of Casting Solidification
2015
Even with decades of study, the complex development of solidification microstructures in cast iron is incompletely understood. Because Fe-C eutectic can produce different morphologies, and even different phases, depending on growth velocities and composition, understanding the conditions under which each forms is important. Directional solidification was used to investigate the effects of alloying additions and solidification velocity on graphite spacing in gray iron. Average and minimum spacing for five compositions, containing varied amounts of Si and Mn, and velocities from 0.5 to 5 µm/s are reported. A critical velocity of around 1 µm/s was observed, above which the graphite structure loses directionality and austenite dendrites appear. A semi-automated MATLAB code was developed for quickly and objectively measuring graphite spacing. The automated results compare favorably with traditional manual measurements, and will allow for more robust measurement of eutectic spacing in systems where the spacing is highly irregular.
Metallurgical and Materials Transactions A, 2018
Macrosegregation is a result of the interplay of various transport mechanisms, including natural convection, solidification shrinkage, and grain motion. Experimental observations also indicate the impact of grain morphology, ranging from dendritic to globular, on macrosegregation formation. To avoid the complexity arising due to modelling of an equiaxed dendritic grain, we present the development of a simplified three-phase, multiscale equiaxed dendritic solidification model based on the volume averaging method, that accounts for the above-mentioned transport phenomena. The validity of the model is assessed by comparing it to the full three phase model without simplifications. It is then applied to qualitatively analyze the impact of grain morphology on macrosegregation formation in an industrial scale direct chill (DC) cast aluminium alloy ingot.
Analysis of Segregation Process in the Solidifying Casting
In the paper the numerical model of alloy solidification is presented. In the first part the segregation model on the level of a single grain is taken into account. Next the similar problem is solved using the essentially simpler approach, in particular the lever arm and the Scheil models are considered. In the final part of the paper the comparison between the solutions obtained is presented and the final remarks are formulated.
Proceedings of Modeling of Casting and Solidification Processes
2004
A Three-Phase Model is developed to simulate the globular equiaxed solidification. The three phases are liquid, solid and air, respectively. We solved the basic conservation equations of mass, momentum, enthalpy for each phase, and considered the thermal and mechanical (drag force) interactions among the phases. Grain nucleation, growth rate (mass exchange), solute partitioning at liquid-solid interface and solute transport are also accounted for. Due to its small density, the air phase floats always at the top region, forming a definable air-liquid melt interface, i.e. free surface. By tracking this free surface, the shrinkage cavity in an open casting system can be modeled. As the temperature and concentration dependent density and solidification shrinkage are explicitly included, the thermo-solutal convection, together with feeding flow and grain movement can be taken into account. This paper focuses on the model description, and the preliminary results on a benchmark ingot casti...
Materials Research, 2020
The solidification control is of extreme importance, because it strongly affects the final casting quality sanity. The structure obtained is generally not homogeneous and gives rise to great variations in composition, with position at small and large scales, which is known as segregation. An understanding of the way segregation occurs in continuous casting is of great importance for steels and in designing post-casting processes. As-cast structures are responsible the reduction in both scale and extension of segregation, because mass transport is dependent on the time required to diffuse a solute over a characteristic distance, e.g., the dendrite spacing that the characterizes the solidification structure. In this work, the effect of pouring temperature in steel slabs on the continuous casting processes are systematically investigated. Relationships between pouring temperature (P T) and center macrosegregation was qualitatively examined. Photomicrographs of specimen taken from transverse sections of steel slabs, shows that macrosegregation is strongly affected by pouring temperature (P T). For solute of carbon, phosphorus and sulfur, has been shown that the pouring temperature (P T) has a significant role on the resulting macrosegregation profiles, while that the elements as such silicon, manganese and aluminum, the said thermal parameter seems not able to affect its macrosegregation profiles. This is due to the fact that the solutes with lower partition coefficients favors segregation during the continuous casting process. It is shown for considered steels, the pouring temperature (P T) influences the position of the columnar to equiaxed transition (CET). Experimental results show that the end of the columnar region is abbreviated when lower pouring temperatures is used in continuous casting process. One can observe that as the pouring temperature (P T) increase in continuous casting process, the secondary dendritic arm spacing (λ 2) increase, i.e., the dendritic morphology became coarsen.
Solidification of Some Casting Alloys of Commercial Significance
Springer eBooks, 2015
This chapter will cover the solidification of some alloys of commercial interest as well as selected numerical models developed to describe and predict the microstructure evolution and defect formation in these alloys. The research community and the commercial entities have produced and continue to produce quite an abundance of numerical models for the prediction of defect occurrence and microstructure development of alloys. For metal casting applications, the most commonly used commercial software are ProCAST and Magmasoft. General commercial codes, such as ABAQUS or Fluent, have also been used in conjunction with specialized routines. This chapter will attempt to illustrate the progress, success, and limitation of both research and commercial models in the prediction of microstructure and related features. 19.1 Steel Steel is a Fe-C-based alloy that solidifies without eutectic. Plain carbon (unalloyed) steel is an alloy whose equilibrium phase diagram (the Fe-C diagram) exhibits partial solid solubility with a peritectic reaction (see Fig. 10.20). Consequently, the solidification microstructure of plain carbon and low-alloy steels is made of equiaxed or columnar α or γ dendrites. 19.1.1 Macrostructure As carbon steel solidifies with a peritectic transformation, the primary grain structure of steel is hard to outline through optical metallography because of the post-solidification recrystallization. Sometimes the macrostructure can be observed in shrinkage cavities, which behave similar to interrupted solidification experiments. The typical dendritic structure of steel revealed by such a technique is presented in
The Solidification Kinetics of Cast Iron using an Improved Thermal Analysis Technique
Cast Metals, 1993
This work proposes a model that is solved numerically to describe the solidification kinetics of castings. In particular, thermal curves and cooling rates are predicted for cast iron of hypoeutectic and eutectic composition. Furthermore, the model is used to establish the influence of the relative locations of the solidifying melt on the cooling curves, the degrees of undercooling, and the heat fluxes. According to the model predictions, the heat generated fluxes become increasingly large as the mould wall is approached. The model is used in predicting the expected eutectic structure, grain size distribution, and interlamellar spacings in a plate-shaped casting of 100 by 100 by 20 mm. In addition, the segregation effects of C, P, and Si are also related to the expected grain structure, and to their effect on the thermal curves. Finally, comparisons between the proposed model and the experimentally determined cooling curves show good agreement.