faceted erosive wear

[Tmoose]

A round shaft is attached to a half blade and operates at fixed angular position in a mineral dust stream. Near the pipe wall the shaft wears to an interesting faceted or angled profile.

The wear probably should be called erosion. Often material specifications list different wear rates at different angles of attack.

At first I figured the resulting angle is a "low wear" angle. Then, for a while I decided it might be the maximum wear angle. Now I'm not at all sure.

Is the real answer obvious and well known to the tribology community? I can try and identify the blade's angle of attack if necessary.

 

[unclesyd]

That looks very much like a rubbing wear phenomena.
Is there any possibility of something getting loose on the shaft and making contact with the blade and sit there rubbing or the shaft and blade?

The reason I mention this is that I've seen very similar wear on dampers where a bushing would come loose and cause the same wear pattern on the damper and shaft