On a Wing and a Cubic Zirconia

Hi,

why should a coating with Zirconia (on the surface) or adding Zirconium as an alloy content in the turbine blades material be better than the todays use of Aluminum and Yttrium in the alloy? (Chromium helps too for oxidation resistance but this is a strengthener whereas the others are thought to generate "only" corrosion protection.)

These are converted to Alumina, Yttria or Zirconia - the oxides on contact with air if hot.

Slow diffusion from the inside will help to replace some of the lost material.

If "sand" (SiO2) hits the hot blade, it will react with the oxides (if sticking) and produce Silicates: mixed oxides for example Al2O3 x Si02 = Al2SiO5 or ZrO2 x SiO2 = ZrSiO4).

All of these are ceramics and no glasses. If to be converted to glass some "glass forming elements" have to be present: Boron, Phosphor.

The problem is much more complicated: the oxides of Nickel, Iron, Chromium and from other constituents of the alloy build up a mixed layer with Al, Zr and Si.

Any change in this layer will change the composition and very likely induce failing adhesion, cracking, spalling, voids...

So there will not be one and only one solution but hopefully a continuous improvement of high temperature strength.

Remaining interesting question: when to go to ceramic blades - if ever?

These will face similar problems but may have better high temperature characteristics but too brittle at low temperature.

RHABE

Remember the foremost reason for coating blading in the first place is to reduce the heat. That is why they are coated using Yttria Stabilized Zirconia Oxide, which is used as a thermal barrier. The metal or alloy coating of the blading is used for two reasons, one is as a bond or base coat and the other serves as corrosion protection. This is due to the oxide scales that form on its surface. I would suspect that the presence of "sand" will produce two types of problems. If the particles are large enough then they will not melt and only act as a blasting media. The ones that due will reduce the thermal behavior of the surface of the blade by densifying the surface causing cracking and lowering the overall operating temperature of the blading system. I wounder how many diamonds you would need to make in order to pay off a jet turbine.

Hello,

I am developing a steam engine for automotive use. It also needs piston crown and cylinder head coatings for insulation purposes. Do either of you gentlemen know how well the stabilized zirconia coatings would work with dry steam, and what kind of U factor per mill one could expect?

Wouldn't the zirconia end up as more of an underlayment or protective layer under the corrosive glass?

Thank You,

Bill G.