1. Centrifugal Casting for High Volume Fraction Ceramic Metal Composite Parts Edward Barnard, Elizabeth Hager, Jenny Lichter, and Kevin McComber May 13, 2004

2. Overview Goals and Methods Design and Materials Theory Processing Part Characterization

3. Goals Our goal was to design a manufacturing process to create a high ceramic volume fraction metal matrix composite (MMC). The project took the process developed by Dr. Jessada Wannasin and scaled it up for part production.

4. Background on MMCs Combine – High moduli of ceramics – High toughness of metals Applications – Sports equipment – Wear-resistant parts for automobiles – Packaging materials for space applications

5. Methods Fabrication methods – Stir casting – Pressure infiltration: gas, mechanical, centrifugal We chose centrifugal pressure infiltration for high pressures and safety

6. Mold Design Two identical aluminum molds designed using CAD, machined on lathes and a milling press Mold interiors coated with boron nitride to ease removal Mating surfaces of molds separated by graphite o-rings to prevent metal leakage

7. Assembly Design Molds were each connected to a half-inch diameter steel tube via Swagelok connectors Added a "tower" to our centrifugation system – held more metal in order to infiltrate complete parts – black tube was used to stabilize the assembly in the centrifuge

8. Materials - Metal Aluminum – optimal choice for MMCs Aluminum has problems – Requires high processing temperatures – Can be reactive Our metal choice: tin-lead – Tin - 15 wt% lead – Tin - 22 wt% lead

9. Materials - Ceramic SiC, BC, Al 2 O 3 particles Most experiments done with SiC particles 50 – 100 microns in diameter Ceramic preforms – Ceramic combined with ethyl silicate binder – Sintered at 1500º C for 1 hour

10. Theory – Threshold Pressures Used data on aluminum infiltration from Dr. Wannasin’s PhD thesis Minimum infiltration pressures: – SiC particles, 7–155 microns: 2–22 atm – Al 2 O 3 particles, 5–20 microns: 8–11 atm Based on moment of inertia we estimated we could achieve P = 50 atm, so P >> P th

11. Theory – Infiltration Time Darcy’s Law for pressure-driven flow Tube–Bundle theory Infiltration time << 1 min Solidification time = 5 min

12. Process – Round 1 Lathed polyethylene master used to create silicone rubber mold Ceramic powder and binder poured into silicone rubber mold to create preform Sintered preform ready for casting Preform set inside mold and mold halves bolted together; molten metal poured into runner

13. Process – Round 2 Entire setup heated at 350  C to re- melt metal Heated setup spun at 700 rpm for 5 minutes Final infiltrated part

14. Infiltration SiC 220 grit – Sintered at 1500 ºC for 1 hour – Spun at ~700 rpm Nearly complete infiltration

15. Characterization using SEM Fully-infiltrated sample Weak interfaces Cracks through SiC particle Boundaries are barriers to propagation

16. Ceramic Volume Fraction Estimated by weight and by imaging By weight: above 70% – too high because we did not account for pores By imaging: – SiC 120 grit (~100 microns): 58.9 +/- 7.1% – SiC 220 grit (~70 microns): 61.3 +/- 11.4%.

17. Backflow Complicated, arbitrarily shaped parts Machined copper disk with a dimple

18. Brinell Hardness Creates deep and wide indentation Appropriate for composite parts Instron compression tester Results: – Tin-lead: 174.4 MN / m 2 – SiC 120 grit MMC: 285.8 ± 51.8 MN / m 2 – SiC 220 grit MMC: 281.4 ± 39.9 MN / m 2 SiC 220 grit 1.9 mm

19. Acknowledgments Jessada Wannasin Toby Bashaw Joe Parse Yin-Lin Xie Edgerton Machine Shop