Numerical Simulation of Solidification Process on Single Crystal Ni-Based Superalloy Investment Castings

布里奇曼投资铸造物的方向性的团结是为可靠、高度有效的煤气的汽轮机 blades.In 的生产的 keytechnology 这份报纸， amathematical 模型为三维( 3D )单个 crystalinvestment 铸造物的团结过程的模拟基于多重片铸造物和炉子墙在 superalloy investme 在 model.Temperaturedistribution 和温度坡度被考虑的基本的热转移 equations.Complex 热 radiationamong

Numerical Simulation of Shrinkage Cavity Formation in Spheroidal Graphite Iron Castings Based on Micro Modeling

A micro-modeling method (MM) for the quantitative prediction of the shrinkage cavity formation in SGiron castings is proposed. The mathematical models describing the volume changes during the solidification ofspheroidal graphite cast iron are established based on the models of solidification kinetics. The shrinkage cavityformation of T-shaped SG iron castings is calculated with MM method. The calculated results are compared with theexperimental results. It is shown that the predicted size, shape and distribution of shrinkage cavity by MM methodare in good agreement with the measured results.

Experimental Study and Numerical Simulation of Directionally Solidified Turbine Blade Casting

汽轮机片样品铸造物的方向性的团结过程在工作被调查。可变退却率用一致 rate.A 在一个退却过程并且与其它相比被使用为热放射转移和方向性的团结过程的微观结构模拟的数学模型基于 CA-FD 被开发方法。温度分发和微观结构被模仿并且与试验性的结果相比。迷路的谷物被预言并且与试验性的结果相比。站台的不平的温度分发是迷路的谷物的形成的主要原因。

Study and Application of Mold Filling Simulation of Shaped Castings

In this paper, an algorithm for simulating fluid flow and heat transfer for mold filling of shaped castings is presented. The main features of the algorithm include: 1) a simple but practical technique based on VOF method to determine free surface, 2) an explicit scheme of enthalpy to solve the energy equation more efficiently, and 3) an effective treatment to modify the flux deviation due to pressure iteration. In order to verify these methods, well controlled experiments have been repeatedly done with both water analog and gray iron pouring experiments to record the flow patterns and temperature variations. The calculated results are in accordance with the experimental ones. For the applications, the simulated initial temperature distribution right after mold filling was used to analyse subsequent solidification and to predict shrinkage defects. Actual castings were poured and tested in a foundry plant. The reuslts show that the defects predication with considering fluid flow effects is more precise than that without considering the effects.

Analysis of solute redistribution and centerline segregation in continuously cast thin slab

A model has been built to calculate the solute redistribution in continuously cast thin slab and the effect of the fluid flow in mush on the centerline segregation was analyzed. The corresponding simulation program was developed by applying the SIMPLER algorithm. The momentum, energy and species conservation equations were solved simultaneously. The macro-segregation of a 3-D thin slab with 900 mm × 50 mm cross section was simulated. The obtained results show that negative segregation forms near the slab surface and severe centerline segregation forms in the mid-thickness plane. The species concentration in the centerline of the slab increases obviously at the final solidification stage.

Generation mechanism and motion behavior of sliver defect in single crystal Ni-based superalloy

Sliver is a common but easily neglected defect in single crystal Ni-based superalloy castings.To date,there is still no unified viewpoint on its formation mechanism and generation causes.In this work,the orientation discontinuity and motion behavior of sliver defects were studied through experiments and numerical simulations.The ultrathin wedge-shaped specimen containing the grain boundary of the sliver and the matrix was prepared at the initial position of the sliver defect for the observation of equal thick-ness fringes.The discontinuity of equal thickness fringes on both sides of the grain boundary was ob-served through a transmission electron microscope,which directly confirms the abrupt change in the orientation between the sliver and matrix from the nanoscale.The crystal lattices at the smooth area and the bulging area of the grain boundary were found to have unusually different arrangements.The irregular lattice arrangement at the bulging area shows that the grain boundary has experienced high-stress deformation.Statistical results of sliver orientation deviation with a further composition analysis show the micro protuberance of the mold shell has a noticeable inductive effect on the sliver generation.Furthermore,a self-developed three-dimensional phase-field simulation model coupled with the spatial topology algorithm is established to simulate the orientation deflection behavior and orientation devia-tion threshold of fractured dendrites.The simulation results indicated that there is an upper limit of the cross-section solid fraction at the fracture position for the motion of the fractured dendrites.When the cross-section solid fraction at the fracture position is higher than this upper limit,it will be difficult to produce large deviation slivers due to the structural limitation of surrounding dendrites.This upper limit does not change with the solidification temperature gradient.

A Modified Cellular Automaton Model for the Quantitative Prediction of Equiaxed and Columnar Dendritic Growth

Since the characteristic of dendrite is an important factor determining the performance of castings, a twodimensional cellular automaton model with decentered square algorithm is developed for quantitatively predicting the dendritic growth during solidification process. The growth kinetics of solid/liquid interface are determined by the local equilibrium composition and local actual liquid composition, and the calculation of the solid fraction increment is based on these two compositions to avoid the solution of growth velocity. In order to validate the developed model, quantitative simulations of steady-state dendritic features over a range of undercooling was performed and the results exhibited good agreement with the predictions of LGK（Liptone Glicksman-Kurz） model. Meanwhile, it is demonstrated that the proposed model can be applied to simulate multiple equiaxed dendritic growth, as well as columnar dendritic growth with or without equiaxed grain formation in directional solidification of AleC u alloys. It has been shown that the model is able to simulate the growth process of multi-dendrites with various preferential orientations and can reproduce a wide range of complex dendritic growth phenomena such as nucleation, coarsening of dendrite arms, side branching in dendritic morphologies, competitive growth as well as the interaction among surrounding dendrites.

Study on Dendritic Growth in Pressurized Solidification of Mg–Al Alloy Using Phase Field Simulation

A multi-grain phase field model coupled with thermodynamic calculation was adopted to describe the dendritic growth in pressurized solidification of Mg-A1 alloy during squeeze casting, in which the effects of the pressure on the Gibbs free energy and chemical potential of solid and liquid phases, the solute diffusion coefficient, and the solute partition coefficient were considered. The individual effect of solute diffusion coefficient, and the Gibbs free energy on the dendritic growth was studied. With the compar- ison of the dendritic growth under atmospheric and elevated pressures, the effect of pressure on the microstructure evolution was discussed. The results showed that the grains are refined, the dendritic growth rate tends to increase and the secondary dendrite arms are more developed as the pressure is increased from 0.1 to 100 MPa, which showed a good agreement with the experimental results of direct squeeze casting of Mg-AI alloy. As the pressure increases, the largest dendritic growth rate can be obtained under the pressure between 200 and 250 MPa, while the growth rate decreases with a further increase of pressure.

Multi-scale modeling of liquid-metal cooling directional solidification and solidification behavior of nickel-based superalloy casting

Liquid-metal cooling(LMC)process can offer refinement of microstructure and reduce defects due to the increased cooling rate from enhanced heat extraction,and thus an understanding of solidification behavior in nickel-based superalloy casting during LMC process is essential for improving mechanical performance of single crystal(SC)castings.In this effort,an integrated heat transfer model coupling meso grain structure and micro dendrite is developed to predict the temperature distribution and microstructure evolution in LMC process.An interpolation algorithm is used to deal with the macro-micro grids coupling issues.The algorithm of cells capture is also modified,and a deterministic cellular automaton(DCA)model is proposed to describe neighborhood cell tracking.In addition,solute distribution is also considered to describe the dendrite growth.Temperature measuring,EBSD,OM and SEM experiments are implemented to verify the proposed model,and the experiment results agree well with the simulation results.Several simulations are performed with a range of withdrawal rates,and the results indicate that 12 mm·min^(-1)is suitable for LMC process in this work,which can result in a fairly narrow and flat mushy zone and correspondingly exhibited fairly straight grains.The mushy zone length is about 4.8 mm in the steady state and the average deviation angle of grains is about 13.9°at the height 90 mm from the casting base under 12 mm·min^(-1)withdrawal process.The competitive phenomenon of dendrites at different withdrawal rates is also observed,which has a great relevant to the temperature fluctuation.