Re: etchants for ni-cr and wc-co

Posted by Gordon England ( on 13:53:16 05/06/06

In Reply to: etchants for ni-cr and wc-co posted by rambabu

Hi rambabu
I assume these are thermal spray coatings. Generally most thermal spray coatings are view in the as-polished condition only. Etching coatings can be difficult and the results can be uneven and inconsistent. Substrate material very often interferes.
For WC/Co and WC/CoCr type coatings though, a useful etchant is Murakami's, which I modify by diluting heavily as it tends to be very aggressive. This is not a pretty etch, but it can indicate the extent of oxidation and formation of metastable phases which are not normally desired. At best you should see no etching.
NiCr alloy coatings I have not etch before, so all I can say is experiment. The only thing I think that you will reveal over that of viewing in the as-polished condition is the grain structure within the splats.
Regards Gordon

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