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

Presented by: Sean LandwehrAdvisor: Prof. Rod Trice

Background on Crack Behavior

No Crack deflection

Crack Deflection

A crack can either deflect at an interface or go straight through it.

Crack

What is Known About Crack Deflection

He and Hutchinson looked at elastic material interfacesFound 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)

2

2

1

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)

Link to Glassy Phase

Well below Tg, crack goes straight through the glassy phaseAround Tg, the crack is blunted by the glassy phase

Glassy Phase

BN

Crack

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

Looking at Elastic/Viscous Interface

Simple structure is neededElastic material needs to be brittle and linear elasticElastic material needs to have constant material properties through the viscous temperature range of glassViscous material must have a wide range of viscositiesProperties of the viscous material need to be well characterized.

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)

Al2O3

Al2O3

Al2O3

Al2O3

AZP Glass

AZP Glass

AZP Glass

General Approach to Making the Laminate

Tape cast the alumina using an aqueous based slurryBurnout binder and fully densify aluminaSpray glass, and heat treatLaminate

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 50m screen to remove large particles10% of slurry weight added in active binder is added

Alumina Sheet Fabrication

Tape Casting Process

Lay down a sheet of mylar with a silicone coatingSet a blade gap of 600mSet motor speed to 1 cm/sPour slurry behind blade

Alumina Sheet Fabrication

Sintering of Alumina

Put green tape samples in between porous alumina substratesBurnout/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

Alumina Sheet Fabrication

Shrinkage Effects

Green tape thickness is ~350m Fired thickness is ~280m, which is ~19% shrinkageLength dimensions shrink ~17% upon firing

Alumina Sheet Fabrication

Spraying AZP GlassExperimental glass from Corning, courtesy of Dr. MorenaReacted Powder Mixed in 1g AZP to 10mL isopropanol20 “passes” are made with the sprayer, letting spray dry after every 10 passes

Preparation of Glass Interface

Forming Glass LayerHeat glass-covered alumina up to 550°C Keep at temperature for 5 hours to remove bubbles form the melted glassFurnace cool, to avoid thermal shock20 “passes” yields ~20m glass layer

Preparation of Glass Interface

Glass Powder

Alumina Sheet

Alumina Sheet

Glass Layer

55

0 °C

/5h

Layering of the Laminate

Stack up glass covered alumina, so that layers of glass and alumina alternatePlace between 2 cordierite setters, and put a brick on top of itHeat up furnace to 550°C and hold for 2 hours, furnace cool

Brick

SettersLaminate

The Laminate

Glass wets both sheets of alumina well.Glass is adhering to the surfaces of both alumina pieces

Problems with Alumina

Waviness, and curvature in alumina sheets made lamination difficult

Problems with Lamination

Problems with AZP Glass

Bubbles cause gaps in the glass layer

Problems in Lamination

Alumina AZP Glass Layer

Gaps in AZP Glass Layer

Conclusions

Alumina/AZP Glass laminates can be madeThe glass can be sprayedFlatter alumina sheets are needed for laminationBubbles in the glass also need to be removed

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

Acknowledgements

Roland Bruyns for his help with tape casting and making alumina sheetsDr. Robert Morena from Corning for helping with glass issues during the projectProf. Trice and the faculty at Purdue for putting up with me this summer