Precision investment casting is widely used in manufacturing complex aerospace and automotive components, such as IN713C superalloy turbocharger turbines. This study focuses on optimizing process parameters to suppress hot tearing defects during the casting of thin-walled turbine blades. A numerical framework combining thermal-stress analysis and hot tearing criteria was developed to predict defect formation mechanisms.
The turbine geometry features 10 curved blades with 0.7 mm thickness connected to a 28 mm central shaft, creating significant thermal gradients during solidification. The gating system consists of a sprue, pouring cup, and three runners arranged at 130° to the turbine axis, as shown below:
The constitutive equations for thermal stress calculation follow the thermo-elastoplastic model:
$$
\{ d\sigma \} = [D_{ep}](\{ d\varepsilon \} – \{ d\varepsilon_p \} – \{ d\varepsilon_T \})
$$
where $[D_{ep}]$ represents the elastoplastic stiffness matrix. The hot tearing susceptibility index (HTI) was calculated as:
$$
\text{HTI} = \int_{t_{\text{coh}}}^{t_s} \sqrt{\frac{2}{3} \dot{\varepsilon}_p : \dot{\varepsilon}_p} \, d\tau
$$
Material properties of IN713C alloy were characterized through experimental measurements and Scheil-Gulliver simulations:
| Property | Value |
|---|---|
| Liquidus Temperature | 1,345°C |
| Solidus Temperature | 1,196°C |
| Young’s Modulus (800°C) | 145 GPa |
| Thermal Expansion Coefficient | 14.2 × 10-6 K-1 |
Process parameter effects were systematically investigated through numerical experiments:
| Parameter | Level 1 | Level 2 | Level 3 |
|---|---|---|---|
| Pouring Temperature (°C) | 1,400 | 1,500 | 1,550 |
| Shell Preheating (°C) | 800 | 850 | 900 |
Thermal analysis revealed critical solidification characteristics:
$$
\frac{\partial T}{\partial t} = \alpha \nabla^2 T + \frac{L}{c_p} \frac{\partial f_s}{\partial t}
$$
where $f_s$ is solid fraction and $L$ latent heat. Blade edges solidified 48% faster than the hub, creating strain localization at blade-root junctions.
The HTI parametric study showed non-linear relationships:
| Condition | Max Stress (MPa) | HTI (×10-4) |
|---|---|---|
| 1,400°C/800°C | 47.2 | 8.9 |
| 1,500°C/900°C | 25.1 | 6.1 |
Optimization recommendations for precision investment casting include:
- Maintain shell preheating ≥900°C to reduce thermal shock
- Use pouring temperatures between 1,480–1,520°C
- Implement progressive solidification through thermal modulators
The numerical framework demonstrated 92% accuracy in predicting actual defect locations when validated against experimental castings. This methodology provides critical insights for precision investment casting of nickel-based superalloy components requiring high surface integrity.