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Design and Additive Manufacturing of Ceramic Cores for Investment Casting

Kadir Tuğrul DEMİRCİ, Büşra Özge İLME, Hasan Tahsin KOÇ, Ahmed MAADY, Oğuz Kaan ÖZKANLI Beyza Nur ULUOĞLU, Mert ÜZEN

Advisors: Assoc. Prof. Dr. Simge ÇINAR AYGÜN, Prof. Dr. Caner DURUCAN, Assist. Prof. Dr. Irmak SARGIN

MetE 22’

Aim

To make use of additive manufacturing instead of injection molding

Limited design capabilities
Higher entry cost

To provide and produce a better ceramic core for investment casting of single crystal turbine blades, by additive manufacturing

Introduction

Hollow turbine blades;

Vital for aircrafts

Thrust-to-weight ratio to assess performance

Affected by working temperature (the higher the better)

Superalloys are used
Cooling channels

Intricate shape to be produced

Figure 1. Cross Section of a hollow turbine blade and its ceramic core [1][2]

Summary

Additive manufacturing of ceramic offers a better solution to produce intricate parts such as ceramic cores
Silica added alumina ceramic cores are believed to give the best properties
The compatibility of silica-alumina slurries with printability for DIW is investigated

In overall, Pluronic F127 is best for injectability and structural integrity

Porosity is essential for leachability

Coarse particles gives more porous structure after sintering

Mechanical properties at high temperature for future work

Ceramic Cores

Produced by injection molding

More effective production methods are possible such as additive manufacturing methods.

With additive manufacturing

Smooth surface finish and complex geometries can be obtained.

Reduces the weight of the turbine blade
It should withstand higher thermal stresses
It should be leachable and the built structure must only remain
Chemical stability is crucial

Alumina Ceramic Cores

with Silica addition

Silica ceramic cores

Low mechanical properties at high temperatures (over 1200°C)

Alumina Cores (Green Body)

Can have 25– 35 MPa flexural strength
Shrinkage is less than 5%
Porosity can be over 30%

Additive manufacturing methods and optimal combination of them may lead to superior ceramic cores

EXPERIMENTAL

Characterization

Slurry Preparation

RESULTS

Injectability

Sintering

Figure 2. SEM image (a) and XRD curve (b) of fine alumina

Figure 5. Average particle size distributions of powders superimposed on one graph

Powder	D_0.1(µm)	D_0.5(µm)	D_0.9(µm)	Range (µm)
Fine Alumina	0.68	0.95	1.61	0.93
Coarse Alumina	9.69	14.4	25.4	15.7
Silica	2.57	3.75	7.5	4.93

Table 1. Corresponding values of average particle size distributions of the powders

Binder for Powders	Injectability	Roughness	Structural Integrity	Slurry Homogeneity
PVA	Poor	Good	Poor	Poor
Pluronic F127	Good	Poor	Very Good	Good
PVP	Very good	Poor	Good	Good

Table 3. Qualitative printability assessment of slurries with respect to binders used

Porosity

Figure 7. Printed powders of different size, along with binders prepared

Figure 3. SEM image (a) and XRD curve (b) of coarse alumina

Figure 10. SEM image of the green body

Average particle size determination was done via three measurements are averaging the size distribution

Figure 6. Preparation of PVA solution at 80 ℃ (1) and slurry (2)

Figure 8. Printed powders of different size, along with binders prepared

Figure 9. Temperature profile of sintering [4]

References

Dong Y., Li X., Zhao Q., Yang J., Dao M., (2017). Modeling of shrinkage during investment casting of thin-walled hollow turbine blades, Journal of Materials Processing Technology, Volume 244.
Ma, D. (2018). Novel casting processes for single-crystal turbine blades of superalloys. Front. Mech. Eng. 13, 3–16
Li, Q., An, X., Liang, J., Liu, Y., Hu, K., Lu, Z., Yue, X., Li, J., Zhou, Y., & Sun, X. (2021). Balancing flexural strength and porosity in DLP-3D printing al2o3 cores for hollow turbine blades. Journal of Materials Science & Technology
Li, H., Liu, Y., Liu, Y., Hu, K., Lu, Z., & Liang, J. (2020). Effects of Solvent Debinding on the Microstructure and Properties of 3D-Printed Alumina Ceramics. ACS Omega, 5(42), 27455-27462.
Rocha, V., Saiz, E., Tirichenko, I., & García-Tuñón, E. (2020). Direct ink writing advances in multi-material structures for a sustainable future. Journal Of Materials Chemistry A, 8(31), 15646-15657. doi: 10.1039/d0ta04181e
Are Ceramic Manufacturing Processes Environmentally Friendly? An Insight into Production. (2022). Retrieved from https://www.syalons.com/2021/03/18/are-ceramic-manufacturing-processes-environmentally-friendly-an-insight-into-production/

Figure 4. SEM image (a) and XRD curve (b) of silica

Figure 12. Acicular mullite phase

Coarse Al with	Porosity (%)	Fine Al with	Porosity (%)
Pluronic F127	35	Pluronic F127	35
PVP	25	PVP	25
PVA	28	PVA	28

Figure 11. Consolidated fine Al with Silica at high magnification

Table 4. Porosities of powders (via Archimedes Method) with the binder solutions prepared

Eco-Friendliness & Sustainability

Compared with injection molding AM does not require mold production for new ceramic cores.

Diversity of processes makes it difficult to assess ecological footprint

Additive manufacturing of ceramics is highly prospective for sustainability

Cost Analysis

Table 2. Powder mixture and binder solution content with the liquid to solid ratio for all possible configurations

Table 5. Monthly cost analysis

Table 6. Capital Costs

Weight of the ceramic core: 50g/part
Batch size: 1000 parts/month
Labor cost is calculated according to average engineer salaries
Electricity price = 0,12 $/kWh

Raw material cost is for 50 kg batch

30.5 kg Pure Alumina
2.6 kg Pure Silica
Binder & Solvent

The Alumina-Silica Ratio is 92% Al, 8% Si
Different slurry compositions are tested

Liquid / Solid Ratio	Powder Mixture	Binder Solution Content
0.40	92% Fine Alumina - 8% Silica	6% PVA - 94% H₂O
0.42	92% Coarse Alumina - 8% Silica	6% PVA - 94% H₂O
0.36	92% Fine Alumina - 8% Silica	5% PVP - 95% H₂O
0.40	92% Coarse Alumina - 8% Silica	5% PVP - 95% H₂O
0.35	92% Fine Alumina - 8% Silica	20% Pluronic - 80% H₂O
0.36	92% Coarse Alumina - 8% Silica	20% Pluronic - 80% H₂O