I've noticed that all of the above are available in a chrome finish. Not certain, but maybe some chainrings are aluminum without chrome finish. It appears some of all of the above are finished with oil or paint. I'm particularly looking at chains and cogs and wondering whether my preference for aluminum or chrome, without oil or paint finish, is backed up by any evidence.

The problem with frictional surfaces having an anodized or paint treatments...it wears off. Fairly quick....and ends up in places like chain pivots.

I suppose anodized doesn't include chrome. So, is chrome better in the short or long term than untreated aluminum? As to the other stuff, I wonder not only about where it goes when it wears off but also what it does for me and the environment.

Aluminum surfaces are either blasted or painted or polished. Not chromed.

I wonder what is used to polish chainrings and cogs. What do people think about chrome on steel chains?

I think I read somewhere that aluminum can be chromed.

Then come back when you can find the source of that info.

The one TiN coated KMC chain I bought had bare rollers within 500mi. And didn't last longer than any standard 11s steel chain.

They can obviously chrome aluminum-- wheel manufacturers have been making chromed alloy rims for decades. The aluminum part needs to be electroplated with copper before applying the nickel chromium-- which won't adhere to bare aluminum.

Chances are good that if you see an aluminum chainring that appears to be chromed, it was really just made smooth and polished after machining.

You must get a stainless steel chain ring that contains 10% or more chromium inside. You can polish it as much as you want and the chromium layer won't wear out.
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It can.

Chrome Plating Aluminum | Electroplating Aluminum - US Chrome