Processing of Alumina/Glass Laminates to Investigate Crack Behavior at Elastic/Viscous Interfaces

1. Processing of Alumina/Glass Laminates to Investigate Crack Behavior at Elastic/Viscous Interfaces Presented by: Sean Landwehr Advisor: Prof. Rod Trice

2. Background on Crack Behavior A crack can either deflect at an interface or go straight through it. Crack Crack Deflection No Crack deflection

3. 2 1 2 What is Known About Crack Deflection • He and Hutchinson looked at elastic material interfaces • Found crack deflection regime to be dependent on ratio of fracture energies and elastic mismatch. He, Evans, & Hutchinson, Int. J. Solid Structures, 31 [24] 3443-3455 (1994)

4. Deviation From He and Hutchinson • Trice found He and Hutchinson was not applicable to a BN/Si3N4 system. • The 1000°C sample showed much crack deflection. Trice R.W. et al., J. Amer. Cer. Soc., 89[9] 2502-8 (1999)

5. BN GlassyPhase Link to Glassy Phase • Well below Tg, crack goes straight through the glassy phase • Around Tg, the crack is blunted by the glassy phase Crack

6. Primary Objective • Investigate crack behavior at elastic/viscous interface • Under what conditions is crack deflection observed • Possible uses: • Energy absorption material • Maximize energy absorption by tailoring viscosity to temperature and strain rate

7. Looking at Elastic/Viscous Interface • Simple structure is needed • Elastic material needs to be brittle and linear elastic • Elastic material needs to have constant material properties through the viscous temperature range of glass • Viscous material must have a wide range of viscosities • Properties of the viscous material need to be well characterized.

8. Al2O3 AZP Glass Al2O3 AZP Glass Al2O3 AZP Glass Al2O3 Choosing the Alumina/Glass Laminate • Laminate • Simple structure • Alumina • Well characterized • Brittle • Linear elastic • Good mechanical stability • Easy to tape cast • Alkali zinc phosphate (AZP) glass • Well characterized • Wide range of viscosities • Low glass transformation range (starts ~400°C)

9. General Approach to Making the Laminate • Tape cast the alumina using an aqueous based slurry • Burnout binder and fully densify alumina • Spray glass, and heat treat • Laminate

10. Alumina Sheet Fabrication Tape Casting Slurry • Mill together: • 17.4 wt% DI Water • 0.8 wt% D-3005 (dispersant) • 81.8 wt% Alcoa A-16SG (alumina powder) • Filter slurry through 50mm screen to remove large particles • 10% of slurry weight added in active binder is added

11. Alumina Sheet Fabrication Tape Casting Process • Lay down a sheet of mylar with a silicone coating • Set a blade gap of 600mm • Set motor speed to 1 cm/s • Pour slurry behind blade

12. Alumina Sheet Fabrication Sintering of Alumina • Put green tape samples in between porous alumina substrates • Burnout/Sinter according to this schedule: • Ramp at 600°C/h to 250°C • Ramp at 60°C/h to 600°C • Ramp at 250°C/h to 1600°C • Hold for 3h • Cool at 600°C/h to 25°C

13. Alumina Sheet Fabrication Shrinkage Effects • Green tape thickness is ~350mm • Fired thickness is ~280mm, which is ~19% shrinkage • Length dimensions shrink ~17% upon firing

14. Preparation of Glass Interface Spraying AZP Glass • Experimental glass from Corning, courtesy of Dr. Morena • Reacted Powder • Mixed in 1g AZP to 10mL isopropanol • 20 “passes” are made with the sprayer, letting spray dry after every 10 passes

15. Preparation of Glass Interface Alumina Sheet Alumina Sheet Forming Glass Layer Glass Powder • Heat glass-covered alumina up to 550°C • Keep at temperature for 5 hours to remove bubbles form the melted glass • Furnace cool, to avoid thermal shock • 20 “passes” yields ~20mm glass layer 550 °C/5h Glass Layer

16. Layering of the Laminate Brick • Stack up glass covered alumina, so that layers of glass and alumina alternate • Place between 2 cordierite setters, and put a brick on top of it • Heat up furnace to 550°C and hold for 2 hours, furnace cool Setters Laminate

17. The Laminate • Glass wets both sheets of alumina well. • Glass is adhering to the surfaces of both alumina pieces

18. Problems with Lamination Problems with Alumina • Waviness, and curvature in alumina sheets made lamination difficult

19. Problems in Lamination Problems with AZP Glass • Bubbles cause gaps in the glass layer Alumina AZP Glass Layer Gaps in AZP Glass Layer

20. Conclusions • Alumina/AZP Glass laminates can be made • The glass can be sprayed • Flatter alumina sheets are needed for lamination • Bubbles in the glass also need to be removed

21. Future Work • Trouble making very flat alumina sheets • Refine tape casting procedure • Resolve setter difficulties • Use pre-made alumina sheets • Trouble removing the bubbles out of the glass • Use vacuum to remove bubbles • Refine spray process

22. Acknowledgements • Roland Bruyns for his help with tape casting and making alumina sheets • Dr. Robert Morena from Corning for helping with glass issues during the project • Prof. Trice and the faculty at Purdue for putting up with me this summer