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

Background on Crack Behavior No Crack deflectionCrack 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 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] (1994) 2 2 1

Deviation From He and Hutchinson Trice found He and Hutchinson was not applicable to a BN/Si 3 N 4 system. The 1000°C sample showed much crack deflection. Trice R.W. et al., J. Amer. Cer. Soc., 89[9] (1999)

Link to Glassy Phase Well below T g, crack goes straight through the glassy phase Around T g, 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 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.

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) Al 2 O 3 AZP Glass

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

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 50 m screen to remove large particles 10% of slurry weight added in active binder is added Alumina Sheet Fabrication

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

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

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 Preparation of Glass Interface

Forming Glass Layer 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 ~20 m glass layer Preparation of Glass Interface Glass Powder Alumina Sheet Glass Layer 550 °C/5h

Layering of the Laminate 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 Brick Setters Laminate

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 made The glass can be sprayed Flatter alumina sheets are needed for lamination Bubbles 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 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