Solid solution softening and hardening by mobile solute atoms with special focus on hydrogen

Mobile solute atoms will affect both kink formation and kink motion. Softening occurs if solute atoms segregate to kinks and if the rate determining step is the formation of kink pairs. Then double kink formation energy is reduced, which can be shown within thermodynamics. With increasing solute concentration the rate of dislocation motion will finally be determined by kink motion. Kink motion is retarded by solute drag, which increases by adding more solute. Under these circumstances hardening is observed.