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Thermal barrier coatings

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Discussion and questions related to the course Practical Engine Building

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I have WPC treated and Cryo treated my entire EJ257 rotating assembly to attempt to make the block to have a longer service life. It will be a daily driver with 300+ KW at the wheels, and up to 375kw on E85. Potential track days and individual cylinder O2 sensors are to be installed for optimum control.

WPC treatment increases part strength, and reduces friction better than any friction reduction coating according to a study conducted by Honda. (Sent to me by WPC) Cryo mainly helps steel and iron components so I think that my custom (To accept +2mm rods with standard stroke for a better Rod to bore Ratio) 2618 8.5:1 JE FSR pistons with grain align have very little to gain from this process.

I am debating a thermal Barrier coating on the piston crown, and I understand the advantages are small but I would like some experienced opinions. my main reason is for the prevention of hot spots and reduce the chance of detonation.

Would the thermal barrier coating end up making the piston expand less under normal operating conditions, and is it reasonable to make my PWC a little smaller? Eg, I was considering a 0.035 would a 0.034 clearance be acceptable after coating? Or should I stick to my original plan?

Do coatings resist carbon build up?

Do Thermal barrier coating come off and cause issues as they are very abrasive like sand grains if they come loose?

Is the thermal barrier worth it considering the crown is already WPC treated, Which is similar to shot-peening so it improves surface strength of the component, is the thermal barrier worth loosing the WPC treated Crown?

Thank you,

Tomas

Which is the most reputable thermal barrier coating in Australia?

Hi Thomas i know guy that has done this for a job so will have a far better explanation of the effects, He is very active on here adam@linkecu and will be a very good help if he sees this. i will drop him a message about it also

Regards Ross

I dont actually have a lot of experience to share about TBC's. Obviously they can be very effective, gas turbine guide blades for instance only last a matter of minutes without it Vs 100's of hours with it, however these are usually highly optimised chemistries with specialised Ion or Plamsa deposition type application, nothing like the very basic "paint on" based product that you will mostly find in the aftermarket automotive world. Their coefficient of thermal expansion is very different to metals (especially aluminium) so are sensitive to thermal shock. I have no idea how they mitigate this with piston dome coatings.

I do have a little reluctance to advise it as I was involved as an expert witness in a court case several years ago where the application or curing temperature the coating company was using for one of these coatings was well above the annealing temperature of the aluminium so the customer ended up with several high dollar engines full of soft/weak engine parts. This was a big franchised international coating company but it was probably more a problem related to their local (NZ) branch with lack of equipment and knowledge rather than a flaw of the product.

In terms of Cryo and WPC benefits I am not convinced, WPC I have less data on but did assess it a little with no evidence of the claimed residual compressive stress effect they claim on the test parts we had done. There was a reduction in friction but this appeared to be mostly due to the embedded solid lubricant that they don't really mention in their literature, rather than anything related to the surface texture, from memory it was blasted with MoS2 at that time.

Cryo I have significant experience, the company I worked for had a cryo chamber and I done extensive research and testing with it over 10 years or so, including trying to prove or disprove the automotive applications I was interested in. In short, we did not find any reliable & measurable mechanical property improvements in any metals besides what you get with steels due to the normal and well understood retained austenite transformation (you do not even need deep cryo to achieve this). Most of the technical articles and studies related to cryo at the time were highly biased, subjective, poorly designed, but with a bit of mystery and good marketing potential to sell something new. We mostly only had the cyro plant for treating landing gear parts for the LC130 skibirds which needed high dimensional stability when hanging out the bottom of an aircraft parked in Antarctica.

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