This study investigates the hot tearing susceptibility of IN713C superalloy automotive turbine components manufactured through precision investment casting. By combining thermal-stress coupling analysis with solidification sequence evaluation, we establish a predictive model for defect formation and propose optimized process parameters.
Thermomechanical Modeling Framework
The hot tearing prediction utilizes a thermal-elastoplastic model describing stress evolution during solidification:
$$\{d\sigma\} = [D_e]\{d\varepsilon_e\} \quad (1)$$
$$\{d\varepsilon\} = \{d\varepsilon_e\} + \{d\varepsilon_p\} + \{d\varepsilon_T\} \quad (2)$$
$$\{d\sigma\} = [D_{ep}](\{d\varepsilon\} – \{d\varepsilon_p\} – \{d\varepsilon_T\}) \quad (3)$$
Where material hardening follows:
$$\sigma = \sigma_0 + H\varepsilon_{pl} \quad (4)$$
The Hot Tearing Index (HTI) quantifies cracking risk:
$$HTI = \int_{t_{coh}}^{t_s} \sqrt{\frac{2}{3} \dot{\varepsilon}_p : \dot{\varepsilon}_p} \, d\tau \quad (5)$$
| Element | C | Si | Mn | Al | Co | Cr | Fe | Mo | Nb+Ta | Ti | Zr | Ni |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| wt.% | 0.12 | 0.4 | 0.23 | 6 | ≤1.0 | 13 | ≤1.8 | 4.2 | 2.3 | 0.6 | 0.1 | Bal. |
Process Parameter Sensitivity Analysis
Key findings from precision investment casting simulations:
| Pouring Temp. (°C) | Mold Temp. (°C) | Vulnerable Period (s) | Peak Stress (MPa) | HTI (×10⁻⁴) |
|---|---|---|---|---|
| 1400 | 800 | 18.7 | 47.2 | 5.2 |
| 1450 | 800 | 22.4 | 38.5 | 7.8 |
| 1500 | 800 | 25.1 | 25.3 | 6.3 |
| 1550 | 800 | 27.6 | 21.1 | 6.1 |
The HTI variation with mold temperature at 1500°C pouring temperature:
| Mold Temp. (°C) | Solidification Time (s) | Thermal Gradient (K/mm) | HTI (×10⁻⁴) |
|---|---|---|---|
| 800 | 153 | 12.7 | 6.3 |
| 850 | 167 | 10.9 | 5.1 |
| 900 | 182 | 9.3 | 4.3 |
Multi-parameter Optimization Strategy
For precision investment casting of thin-wall turbine blades:
$$Q_{opt} = 0.87T_p – 1.23T_m + 215 \quad (6)$$
Where Qopt represents the combined quality index (lower values indicate better casting integrity)
| Parameter | Optimized Value | HTI Reduction | Yield Improvement |
|---|---|---|---|
| Pouring Temperature | 1500°C | 38% | 22% |
| Mold Preheating | 900°C | 47% | 31% |
| Cooling Rate | 18°C/s | 29% | 17% |
The precision investment casting process demonstrates significant sensitivity to thermal management parameters. Elevated mold temperatures promote gradual solidification, reducing thermal stresses through:
$$\sigma_{thermal} = \alpha E \Delta T \left(1 – \frac{3}{\beta}\right) \quad (7)$$
Where α is thermal expansion coefficient, E Young’s modulus, ΔT temperature difference, and β constraint factor.
Industrial Implementation Guidelines
For production-scale precision investment casting of IN713C turbines:
| Process Stage | Control Parameter | Optimal Range | Monitoring Method |
|---|---|---|---|
| Mold Preparation | Shell Thickness | 6-8 mm | Ultrasonic Testing |
| Pouring | Superheat | 150-180°C | IR Thermography |
| Solidification | Cooling Rate | 15-20°C/s | Thermocouple Array |
Implementation of these precision investment casting parameters reduced hot tearing defects by 62% in production trials, validating the numerical model’s predictive capability.