system
Given the following post, respond as if you're commenting on Reddit:
human
Why does silver have a really high coefficient of friction with itself, but low when it has friction against other materials?
gpt
Silver is relatively soft and has a low strain hardening coefficient (deforming the surface doesn't make it very hard).  At the same time, it has a relatively high adhesion with many metals, a low cohesion  (self bond strength), and a low melting point.  

The combination of all these properties results in a thin transfer layer of silver to mating surface of dissimilar (harder) metals, which keeps the local surface bond size and Strength low, resulting in low friction.

For self- mated silver pairs, the soft metal results in local contact areas that grow relatively large. This results in high friction.