High velocity sliding at a compressed Al(111)/Al(100) interface*

We discuss high velocity sliding at a compressed Al(111)/Al(100) interface sliding in the $1\overline{1}0$ direction at a pressure of 15 GPa. Three temperatures are considered, T=232, 464 and 696 K. System sizes are $1.4 10^{6}$ atoms .We find that for velocities above a critical velocity, $v_{c}$, the frictional force scales as $(v/v_{c})^{-\beta}$ with $\beta\approx 3/4$. We discuss the temperature and size dependence of $v_{c}$. We find that below $v_{c}$ the frictional force is an increasing function of velocity with an initial linear dependence. Above $v_{c}$ there is a regime of interfacial instability characterized by a (100) transformation front moving into the (111) material. This is followed by a fluid regime for which a Couette flow profile develops at the interface, the thickness of which grows with increasing velocity.