Titanium alloys are widely recognized for their low density, high specific strength, excellent corrosion resistance, and biocompatibility. These properties make them indispensable in aerospace, marine, and chemical industries. However, high manufacturing costs hinder broader applications. Precision investment casting, a near-net-shape technology, addresses this challenge by minimizing material waste and machining requirements. This study demonstrates the successful fabrication of a ZTC4 titanium alloy impeller with intricate curved blades using optimized investment casting techniques.
1. Process Design and Optimization
The impeller features four open-type blades with varying cross-sections (minimum thickness: 3.8 mm) and a central hub (φ116–186 mm). Key process innovations include:
$$ S(r) = S_0 + \frac{(r – r_{\text{min}})}{(r_{\text{max}} – r_{\text{min}})}(S_{\text{max}} – S_{\text{min}}) $$
where $S(r)$ represents the shrinkage compensation at radius $r$, with $S_{\text{min}}=1.0\%$ and $S_{\text{max}}=2.0\%$. Anti-deformation corrections followed a similar gradient:
| Region | Shrinkage (%) | Anti-Deformation (%) |
|---|---|---|
| Blade Root | 1.0 | 0.8 |
| Mid-Blade | 1.5 | 0.6 |
| Blade Tip | 2.0 | 0.5 |
2. Gating System and Shell Fabrication
A top-pouring system with five radially distributed gates ensured laminar flow:
$$ v_{\text{fill}} = \frac{Q}{nA} $$
where $v_{\text{fill}}$ = filling velocity (0.8–1.2 m/s), $Q$ = volumetric flow rate, $n$ = number of gates (5), and $A$ = gate cross-sectional area. The shell system employed:
| Layer | Material | Thickness (mm) |
|---|---|---|
| Primary | ZrO2 | 0.3–0.5 |
| Secondary | Al2O3 | 1.2–1.5 |
| Backup | Mullite | 2.0–3.0 |
3. Melting and Quality Control
Vacuum arc remelting parameters ensured metallurgical quality:
$$ P_{\text{vac}} \leq 5 \times 10^{-2} \, \text{Pa} $$
$$ T_{\text{melt}} = 1700 \pm 20^\circ \text{C} $$
| Parameter | Value |
|---|---|
| Arc Current | 28–36 kA |
| Voltage | 34–41 V |
| Coolant Temperature | <45°C |
4. Results and Validation
The precision investment casting process achieved:
- Surface roughness: Ra 3.2 μm
- Dimensional accuracy: CT9 per GB/T6414
- X-ray inspection: Class C per GJB2896A
Chemical composition met ZTC4 specifications:
$$ \text{Ti} – 6\text{Al} – 4\text{V} – \text{Fe}_{\leq0.3} – \text{O}_{\leq0.2} $$
This precision investment casting methodology reduced production costs by 42% compared to machining from billet, while shortening lead time by 60%. The success demonstrates the viability of advanced investment casting for complex titanium components in critical applications.