Transition in superelasticity for Ni_55−xCo_xFe₁₈Ga₂₇ alloys due to strain glass transition

¹ School of Materials Science and Engineering, Beijing Institute of Technology - Beijing 100081, China
² X-ray Science Division, Argonne National Laboratory - Argonne, IL 60439, USA

^a ydwang@mail.neu.edu.cn

Received: 22 November 2011
Accepted: 30 April 2012

Abstract

Here we report a transition in superelastic hysteresis loop from sharp with plateau to smooth without plateau for a Ni_55−xCo_xFe₁₈Ga₂₇ (x=0–12) alloy system with increasing Co substituting for Ni up to 10 at.%. With the Co content reaching 10 at.%, the alloy exhibits the obvious characteristic of the strain glass transition, i.e., the frequency-dependent shift in temperature of the internal friction peak and frequency-dependent dip temperature, T_g, of the storage modulus following the Vogel-Fulcher relationship. The high-energy X-ray diffraction provides the direct evidence that the smooth hysteresis loops stem from a finite avalanche martensite transformation mode, inducing a long-range inhomogeneous stress field in the remained parent phase during deformation.