SHRINKAGE OF ARC SPRAYED COATINGS

[Vijay Deshpande]

Dear All, Is there any data available on shrinkage coefficiant of arc sprayed coatings and its effect on performance of coatings.
regards
Vijay Deshpande

[Gordon]

Hi Vijay

Some comparative shrink values (mainly combustion wire sprayed coatings) taken from an old Metco handbook and old technical bulletins. I think these values would also be reasonably applicable to arc sprayed coatings as well. Please bare in mind that the test method is not described and that the values are only accurate for comparative purposes to that particular test only.

0.1%C low carbon steel (Spasteel 10) 0.008 shrink inch/inch
0.25%C carbon steel (Sprasteel 25) 0.006
0.8%C high carbon steel (Spasteel 80) 0.0014
Low carbon alloy steel (Spraysteel LS) 0.002
Austenitic Stainless steel 316 type (Metcoloy 1) 0.012
Martensitic Stainless 13%Cr steel (Metcoloy 2) 0.0018
Aluminium 0.0068
Silicon Aluminium (SF Aluminium) 0.0057
Aluminium bronze (Sprabronze AA) 0.0055
Brass (60Cu/40Zn) (Sprabronze TM) 0.009
Bronze (95Cu/5Sn) (Sprabronze P) 0.010
Zinc 0.010
Molybdenum 0.003


The amount of shrink a coating undergoes during spraying will significantly effect the coatings residual stress content. Coatings with high shrink tend to form highly stressed coatings which have low thickness limitation values and can be more prone to cracking, like that of austenitic stainless steels and plain low carbon steels. On the other hand coatings like the martensitic 13%Cr steels and 0.8%C steels having low shrink/low stress can be used for very thick coating build-ups.

[Vijay Deshpande]

Thanks for this information. As i found out localised interlayer disbonding in SS316 deposit. This phenomenon is hardly noticed in 13% Chrome steel coatings. Is this debonding is due to resudual stress?
regards
Vijay Deshpande

[Gordon]

Hi Vijay

Possibly, though if you are keeping within the coatings thickness limitation of around 0.030" there should not really be a problem. A good pre-heat will be benificial (something not always done with arc spray) and not spraying too thick per pass.

If you need to achieve thick coatings, use 13Cr steel to build up thickness and top off with 316.