Do ZrN coated end mills reduce tool wear over uncoated tools with low SFM?

[FrodoLoggins]

So the benefit of ZrN is to (I think) reduce friction and therefore let one run the tool faster without non ferrous materials gumming up. But if I'm running a half inch end mill with plenty of coolant at only 6000 RPM, I'm well under the max SFM manufacturers usually recommend. I think lower than the minimum SFM actually. So would I just be wasting money on a coating I don't need and getting a tool with less sharp cutting edges or is it worth it?

 

[Milland]

To some degree, it depends on the chemical characteristics of the coolant, and how well it acts to lubricate and chemically isolate materials you're cutting from the carbide tool. Under conditions where you have an ideal coolant lubricity and chemistry, you are likely fine using uncoated carbide.

There is another issue, though. Carbide cutters are a composite, the actual carbide particles are bound together with a cobalt (usually) matrix material ("glue"), and cobalt can react with water in the coolant and get leached out, damaging the cutting edges.

In that scenario, a ZrN coating can protect the tool from leaching, helping to maintain the cutting edge (even if now very slightly rounded). So it's not just friction, it's chemical isolation that is a benefit from from the right coating.