Microstructural Aspects of THERMAL Fatigue Behavior of Shape Memory Alloys & Microstructural Developments Through CONTROLLED Marforming Operations

Microstructural aspects oF thermal fatigue behavior of shape memory alloys & microstructural developments through controlled marforming operations

Ritwik Basu^a+, Lokendra Jain^a, Bikas Maji^b, Madangopal Krishnan^b, KV ManiKrishna^b, Indradev Samajdar^a and Prita Pant^a

^a Department of Metallurgical Engineering & Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai-400 076

^b Materials Science Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India

 

presenting author: ⁺ basu.r@iitb.ac.in

Shape memory alloys (SMAs) of Ni-Ti are used in applications such as robotics, aerospace and medical due to their technologically attractive properties. In many of these applications, the devices made from Ni-Ti alloys are expected to perform the desired operation repeatedly, as actuators and sensors, without any considerable change in their properties.

One of the critical aspects in the development of these shape memory based actuator devices is the stability of their response to thermal cycles. Thermal Cycling results in fatigue i.e. decrease in their response with increasing number of cycles, and determines the lifespan of the devices.

In the present work we investigate the thermal cycling response of nickel-rich Ni-Ti and Ni-Ti-Fe shape memory alloys. Our focus is to estimate non recoverable strain in these alloys and relate it to microstructural features such as grain size distribution, texture and misorientation in grains.

Secondly we have tried to explore microstructural developments through controlled 'marforming': deformation in the martensite phase followed by phase transformation to austenite. These, in turn, may affect recoverable strain and the transformation temperature. Though possibilities of 'marforming' are usually acknowledged; our understanding of microstructural developments through 'marforming' is, at best, limited. This was the motivation behind the present study.