Martensitic transformation kinetics and shape memory effect in Co–Ni alloys

Abstract

The shape memory effect (SME) and martensitic transformation kinetics in Co–Ni alloys were studied. The degree of SME decreased with increasing Ni content, and was proportional to the pre-existing ϵ martensite content, suggesting that the SME in Co–Ni alloys is related to the coalescence of the pre-existing ϵ plates. Thermal cycling (α ϵ) increased the ϵ martensite content, and the SME became greater with an increasing number of thermal cycles. The martensitic transformation kinetics of Co–Ni alloys can be expressed as Y = 1- exp[-0.00526(M _s-25)], where Y is the volume fraction of ϵ martensite and M _s is the starting temperature of martensitic transformation (°C).