Thermal Barrier Coatings over Steel and Aluminum 1

[KimWonGun]

I am experimenting with thermal barrier ceramic coatings and observed that a particular composition consistently adheres to a steel substrate but inconsistently adheres to an aluminum substrate (1 of 3 to 1 of 4). While it appears clear that the difference in the thermal expansion rate between the TBC and aluminum is sufficient to lead to spalling compared to the same TBC and steel, why is the result inconsistent with the aluminum substrate? After several test batches, the coating never fails with steel. I am completely baffled. What am I overlooking?

 

[TomDOT]

Describe the initial condition, surface preparation and cleaning methods for each.

For example, if you are abrasive blasting the steel but only solvent-wiping the aluminum - you are providing a mechanical "tooth" or texture on the steel which vastly improves adhesion when compared to a smooth surface.

 

[KimWonGun]

Preparation was the same for both the steel and aluminum pieces. They were heated to burn off any oils, grit blasted, and cleaned with acetone.

 

[TomDOT]

I have seen reference to aluminum oxide as the preferred grit for blasting aluminum. I mostly see steel blasting, so I don't have a good reference handy.

 

[KimWonGun]

I am using (recycled) aluminum oxide grit for both the steel and aluminum substrates.

 

[TVP]

If you are using the same media for both, then you are contaminating the Al surface with Fe and iron oxide.