Influence of crystalline phase volume fraction on the two-way shape memory effect in amorphous–crystalline Ti40.7Hf9.5Ni44.8Cu5 alloy

The two-way shape memory effect (TWSME) has been studied in an amorphous–crystalline thin ribbon of Ti40.7Hf9.5Ni44.8Cu5 shape memory alloy with different volume fractions of the crystalline phase. It is found that an increase in the volume fraction of the crystalline phase results in a non-monotonic variation in the value of the TWSME. A maximum strain of 1.1% is observed in the thin ribbon with a 50% crystalline phase. It is found that the TWSME in amorphous–crystalline Ti40.7Hf9.5Ni44.8Cu5 alloy is due to two mechanisms: the formation of high internal stresses on the amorphous/crystalline interfaces due to incompatible strain in amorphous and crystalline phases and the stress caused by defects induced in the crystalline phase during deformation. If the volume fraction of the crystalline phase is 50% or less, then the main contribution to the total TWSME is given by the formation of the internal stresses on the amorphous/crystalline interfaces. In this case, the TWSME value depends on the density of the amorphous/crystalline interfaces, plastic strain and volume fraction of the alloy undergoing a phase transition. If the volume fraction of the crystalline phase is higher than 50%, then the TWSME is due to the formation of the internal stresses on the defects in the crystalline phase and the TWSME value depends on the plastic strain in the crystalline phase and the volume fraction of the crystalline phase.