1. Introduction
In the fields of aviation jet engines, ship gas turbines, and industrial gas turbines, high – temperature gases are commonly used to drive turbines. The blades of turbines, as crucial components, are exposed to harsh environments of high temperatures and thermal corrosion. For example, the working temperature of a typical gas turbine exceeds 500 °C [1]. Superalloys, with their excellent oxidation resistance, thermal stability, fatigue resistance, and creep – rupture properties, have found extensive applications in such scenarios [2 – 5].
K213 is an iron – nickel – chromium – based cast superalloy. It contains elements like Al and Ti, which form the γ’ phase and achieve precipitation strengthening. W is used for solid – solution strengthening, and trace amounts of B strengthen the grain boundaries. This alloy has an excellent casting process and good comprehensive properties below 750 °C [6 – 7].
In recent years, superalloy components tend to be more precise and thinner – walled, posing higher requirements for precision casting processes. The traditional experimental process has drawbacks such as high trial – and – error costs and long cycles. Computer – aided design, however, can significantly reduce these costs and shorten the process design cycle. Many domestic and foreign studies have been carried out on simulating the casting and solidification processes of blades. For example, the Central Iron and Steel Research Institute in China used computer simulation for superalloy precision casting and determined the optimal process plan, which significantly reduced casting defects and production costs [11]. Shenyang Aerospace University simulated the filling and solidification process of K438 alloy liquid in the investment casting process using finite – element analysis and determined the best gating system and process [12]. In foreign countries, many scholars have combined high – throughput methods with numerical simulations and applied them to optimize precision casting process parameters to improve the comprehensive performance of castings [14 – 16].
This study aims to address the issues of complex shapes and potential defects in the precision casting of superalloy blades. The MAGMA casting simulation software is used to simulate the filling and solidification process of K213 superalloy in the precision investment casting of typical blades. The focus is on researching the distribution of the fluid velocity field during the filling process, the solid – phase fraction, temperature field, and void distribution during the solidification process. By determining the likely locations of casting pores, the reliability of the designed gating system is verified, providing a reliable theoretical basis for on – site tests and production.
2. Experimental Method
2.1 Material Selection
The K213 cast superalloy master alloy was selected for the experiment. Its chemical composition is shown in Table 1. The melting point of the K213 alloy ranges from 1324 to 1361 °C, the density is \(\rho = 8.14~g/cm^{3}\), and the expansion coefficient is \(18.61×10^{-6}^{\circ}C^{-1}\) between 20 – 800 °C.
| Element | Content (%) | Element | Content (%) |
|---|---|---|---|
| C | ≤0.10 | B | 0.05 – 0.10 |
| Cr | 14.00 – 16.00 | Fe | Balance |
| Ni | 34.00 – 38.00 | Mn | ≤0.50 |
| W | 4.00 – 7.00 | Si | ≤0.50 |
| Al | 1.50 – 2.00 | S | ≤0.015 |
| Ti | 3.00 – 4.00 | P | ≤0.015 |
| Table 1: Chemical Composition of K213 Cast Superalloy Master Alloy |
2.2 Component Model
According to the requirements of a certain company, the simulated component is an impeller blade of a turbine. The component model is shown .
2.3 Simulation Software and Parameters
The MAGMA casting simulation software was used to simulate the casting process of K213 alloy blades. The filling and solidification processes were analyzed to study the temperature field and the formation and distribution of defects during the casting process, providing guidance for actual production. Gravity casting was adopted, with a gravitational acceleration of 9.8 m/s². The basic parameters included a weight factor of 0.8, a relaxation factor of 1.6, an initial time step of 0.0001 s, a heat transfer coefficient of 0.023 between the casting and air, and between the casting and the mold, and a pouring temperature of 1550 °C.
The blade is a complex – shaped casting. The SolidWorks 3D solid modeling software was used to model the entire gating system. A top – pouring method was used to pour 4 alloy blades at a time, with each blade weighing 3 kg. The gating and runner systems were used to feed the solidification process of the blades. The MAGMA casting simulation software was used for meshing, with a mesh parameter of 1 mm.
3. Results and Analysis
3.1 Solid – Phase Fraction during the Filling Process
Figures 2 and 3 show the solid – phase fraction during the filling process. The longitudinal sectional view in Figure 3 can be used to observe the solid – phase fraction distribution inside the blade and the gating system. As can be seen from the figures, during the pouring process of the blade part, the alloy liquid remains in a liquid state all the time, which enables complete filling of the blade part. The filling is completed in 15 s, and solidification starts at the blade edge at 25 s. After the blade is completely solidified, the runner starts to solidify, and the last solidification occurs at the center of the connection between the gate and the runner. This indicates that the designed gating system can ensure the proper solidification sequence of the casting.
3.2 Temperature Field Simulation Results and Analysis
Figures 4 and 5 show the temperature field distribution during the pouring process. The longitudinal sectional view in Figure 5 can be used to observe the temperature field distribution inside the blade and the gating system. During the pouring process of the blade part, the alloy liquid remains at a high temperature of approximately 1500 °C throughout. After 3 s, the filling of the blade part is completed, and the temperature at the blade edge begins to drop. The lowest temperature is about 1400 °C, which is still higher than the alloy melting point, so defects are unlikely to occur. After 15 s of filling, the temperature in some areas at the blade edge drops to about 1230 °C. Combining with the analysis results of Figures 2 and 3, solidification starts at the blade edge at 25 s. After 15 minutes, the temperature at the center of the connection between the gate and the runner is still around 1300 °C, and the temperature in other parts has dropped below the melting point. This shows that the designed gate and runner can feed the blade part during solidification.
3.3 Fluid Velocity Field Simulation Results and Analysis
Figure 6 shows the simulation results of the velocity field during the filling process. At 3 s, the pouring of the blade part is completed, but there is still some disturbance at the blade edge, and a small amount of gas entrapment occurs in the two outermost blades. However, as the subsequent pouring progresses, this disturbance is unlikely to cause casting defects. At 4 s, the alloy flow in the blade part is completely stationary. At 15 s, the casting is completed, and a significant drop in the gate liquid level can be observed, indicating that the gate and runner play a good role in feeding.
3.4 Void Simulation Results and Analysis
Figure 7 shows the simulation results of voids during the pouring process. It can be seen that during the pouring process, voids are formed in the centers of the two outermost blades due to the disturbance of the pouring process. However, as the pouring progresses, under the pressure of the molten metal, the voids rise continuously and finally concentrate at the gate and runner.
4. Conclusion
This study focused on the numerical simulation of the filling and solidification processes of K213 superalloy in precision investment casting using MAGMA software. The fluid velocity field, solid – phase fraction distribution, temperature field distribution, and void distribution were analyzed, and the possible locations of casting pores were determined, verifying the reliability of the designed gating system. The main conclusions are as follows:
(1) During the pouring process of the blade part, the alloy liquid remains in a liquid state, ensuring complete filling of the blade part. After the blade is solidified, the runner starts to solidify, and the last solidification occurs at the center of the connection between the gate and the runner.
(2) The temperature field simulation results show that after the filling is completed, the temperature at the blade edge starts to drop first, and the temperature increases in a gradient from the blade top to the gate. The center of the connection between the gate and the runner remains at a high temperature, while the temperatures in other parts drop below the melting point.
(3) The fluid velocity field and void simulation results show that there is a small disturbance in the blade part at the initial stage of filling, and the alloy flow in the blade part is completely stationary at 4 s. After the casting is completed, a significant drop in the riser liquid level can be observed, and the final solidification voids concentrate at the gate and the runner.
This research clarifies the evolution process of the flow field and temperature field during the solidification of K213 superalloy, accurately predicts the location and severity of casting defects, and provides a solid theoretical support for the design of the precision casting process of K213 superalloy blades. It also has important reference significance for the design of superalloy precision casting processes.
5. Future Research Directions
Although this study has achieved certain results, there is still room for further research. Future research can be carried out in the following aspects:
(1) Optimization of process parameters: Further adjust and optimize the process parameters such as pouring temperature, mold pre – heating temperature, and cooling rate to further improve the quality of castings.
(2) Multi – material simulation: Consider the interaction between different materials in the casting process, such as the influence of the mold material on the casting quality.
(3) Validation through physical experiments: Conduct physical experiments to verify the simulation results, and further improve the simulation model based on the experimental data.
(4) Integration with other manufacturing processes: Explore the combination of precision casting with other manufacturing processes to achieve more complex and high – performance component manufacturing.
In conclusion, the research on the precision casting process of iron – base superalloys blades through numerical simulation is a continuous and evolving field. With the continuous development of technology, more accurate and efficient casting processes can be expected to be developed, which will promote the development of related industries.
