The Sensitivity of Investment Casting Simulations to the Accuracy of Thermophysical Property Values

Abstract

In this study, the importance of the accuracy of the thermophysical property to a simulation of an investment cast directionally solidified nickel-based superalloy turbine blade was investigated. CMSX-4 was chosen as the base alloy. The effect of the thermophysical properties on the thermal field and solidification microstructure was studied using a coupled macromesoscale model. Relevant thermophysical properties examined include density, specific heat (enthalpy) and thermal conductivity in both the liquid and the solid phases. Commercial finite-element analysis software, ProCAST, was used as the macroscale model to solve the heat and mass transportation equations. An in-house mesoscale code was used to simulate the dendritic solidification structure including microsegregation. During the macroscale analysis, the simulation results were compared to an idealized turbine blade previously cast under industrial conditions. In the mesoscale simulation, the response of primary arm spacing and segregation range was examined. The temperature prediction and the thermal gradient in the liquid show the greatest sensitivity to density and solid state thermal conductivity. Primary arm spacing is most sensitive to density and specific heat. Segregation range shows greatest sensitivity to density and thermal diffusivity in the solid.

Alloy Thermal Physical Property Prediction Coupled Computational Thermodynamics with Back Diffusion Consideration

“…Lee and coworkers investigated the sensitivity of investment casting simulations to the accuracy of thermo-physical properties. [17] They found that the temperature prediction and thermal gradient in the liquid are the most sensitive to the accuracy of the input values used for density and thermal conductivity in the solid. Thermal conductivity in the liquid, specific heat, and density have similar levels of influence on solidification time; increasing their values increases the local solidification time.…”

“…Among all the thermo-physical data, the temperature dependent density is critical for the accurate simulation of solidification microstructure and defect formation. [17] A database has been developed containing molar volume and thermal volume coefficients of expansion of liquid, solid solution elements, and intermetallic phases. This is linked to the thermodynamic calculations mentioned above.…”

The Conditions for Application of Foundry Simulation Codes to Predict Casting Quality

“…Deviations in the accuracy of forecasts are most commonly caused by material data mismatches in the conditions of production in the foundry. The problem of the sensitivity of the model to the errors of coefficients has been developed, among others, in [10][11][12]. The creators of casting simulation codes, as a principle (customary) do not take responsibility for the quality of the parameters contained in the database and at the same time they suggest modifications of material data provided there and supplementing the database with material parameters and the boundary conditions corresponding to the material and assortment conditions of casting in the particular foundry.…”

Investment casting of nozzle guide vanes from nickel-based superalloys: part I – thermal calibration and porosity prediction

“…For example, Sahai and Overfelt [34] reported a HTC in the range 50-5,000 W m −2 K −1 for IN-718 Ni-based superalloy. The HTC at the mold-wrap, moldenclosure, and wrap-enclosure interfaces have less influence on the final result of the thermal model as shown by Yuang et al [35]. Thus, it was assumed that they were constant with temperature and time, and the data from the ProCAST database were used ( Table 2).…”