THermal Spray and Hard Crome Coating

[Met.Eng.]

Is anybody try to coat dimension restoration by thermal spray tech and apply top coat by HardCrome coating? Is Cromic acid reaction with thermal spray coating? What kind of dimension restoration material do we use ?

[Vadim Verlotski]

Is anybody try to coat dimension restoration by thermal spray tech and apply top coat by HardCrome coating? Is Cromic acid reaction with thermal spray coating? What kind of dimension restoration material do we use ?

Hi Met.Eng.,

Almost all thermal spray coatings have porosity and microcracks up to the base material. When one a coated part is immersed in chrome bath (CrO3 + H2SO4) the steel surface corroded below the sprayed layer and the layer flake off.
There are a pair of dense spray coatings with good adhesion to the substrate, for example, MCrAlY layers applied by VPS, or remelted layers of NiCrBSi, but I think that such layers can not be chrome plating. The same is true for all carbide-layers (Cr3C2-NiCr and WC-Co) - hard Chrome will not hold at it.

Regards

[Gordon]

I have come across 13 Cr steel (Metcoloy 2) coatings being successfully hard chromium plated. I believe the coatings were sealed prior to plating. Long time ago, So no details.

A 13Cr steel coating like above would provide a good low stress, high thickness base coating.

Suggest you experiment first

[shantanu]

We've had a very successful experience of hard chrome plating over Metcoloy II coatings sprayed using ARC pray for a cylinder manufacturing plant, for one of thier piston rods, which was badly pitted

Customer would not have accepted thermal spray coating and was insistent on Hard Chrome. The pitted surface was too deep for only hard chrome, so we experimented on hard chrome after thermal spray

Came out very succesfully and the hard chrome was finished ground to mirror polish!

Regards

Shantanu

[Met.Eng.]

Tnx for ur answer