C2.

Project title: Wear resistance of NiTi shape memory alloys

Shape memory alloys (SMAs) are unique due to the reversible phase transition between the low-temperature martensite phase and the high-temperature austenite phase. Nickel titanium (NiTi) SMA exhibits the well-known shape memory (SME) and superelasticity (SE) effects. Superelastic behavior refers to a case where a reversible austenite-martensitic phase transition can be induced by applied stress and is recoverable as the stress is removed. Due to its outstanding superelastic behavior, NiTi SMA has been increasingly used in medical surgery and considered as a possible functional material for microelectromechanical systems (MEMS). In these applications, the stress-induced phase transition process is unavoidable due to the local high contact pressure, and therefore may play an important role in the wearing of NiTi.

When the temperature of the martensite phase is increased during the wearing test, part of the rod samples will attain the Af temperature. This part of the rod will transform to austenite. At the same time, the imposed stress can lead to the formation of the stress-induced martensite (SIM). This SE part of the rod is very elastic and may help in the improving the overall wear resistance of NiTi SMA.

Supervisor: Dr Jonathan C Y Chung (appchung@cityu.edu.hk)

Suitable for: M.Phil. and Ph.D.