Cr3C2 Ni-Cr coating on Aluminium

[ehsan]

Hi
Before I coated Cr3C2 NiCr on some steel parts with gas HVOF and did not have any problem.Recently I coated that on aluminium cylender and during the test we saw creation of cracks on the coat.specially this cracks is in the section of cylender that we have termal shock(between cold and hot section).Do you have any idea?
Max temp of this cylender is 350 C.Is it possible that the thermal expantion coefisient of Aluminium and coat is too different?
Regards

[Simon Kim]

Hello ehsan,

If I should have coat the cylinder coating, I would like to try precoat.
Aluminum has high heat conductivity.
However carbide coating material makes high tensile stress during cooling.
So ductile metallic coat is used for this case, such as Ni-Al or NiCrBSi hard facing material etc.
Because they have lower heat condcutivity than aluminum and their ductility prevents thermal stress crack.
If you want to have higher hardness, choose hard facing materials.
Or if you want to have higher ductility, choose Ni-Al materials.

Simon

[sreenuvundela]

Hi

I agree with Simon

if u do not want to carry bond coat then you have to plan your coating procedure such that the temperature raise in the substrate (Al) is below 150 degree centigrade by providing forced cooling system & carrying coating with time intervals.

Regards,
SREENIVAS

[djewell]

The thermal expansion coefficients of aluminum and CrC are very different. Keep your aluminum part cool while you spray it, and you will have success. 350C is extremely hot for any coated part.

[ehsan]

djewell
350C temperature is not during coating.the work temperature of parts in engine is 350C.