A number of alloys with the L1 2 structure (e.g., Ni 3 Al, Ni 3 Ga, Ni 3 Ge, Ni 3 Si), show yield strength anomalies. The L1 2 structure is a derivative of the face-centered cubic crystal structure. For these alloys, the active slip system below the peak is ⟨110⟩{111} while the active system at higher temperatures is ⟨110⟩{010}. The hardening mechanism in these alloys is the cross slip of screw dislocations from (111) to (010) crystallographic planes. This cross slip is thermally activated, and the screw dislocations are much less mobile on the (010) planes, so the material is strengthened as temperatures increases and more screw dislocations are in the (010) plane. A similar mechanism has been proposed for some B2 alloys that have yield strength anomalies (e.g., CuZn, FeCo, NiTi, CoHf, CoTi, CoZr).