Thermodynamic, Structural Properties and Transformation Behavior in CoNiGa Alloys from First Principles Conference Paper uri icon

abstract

  • CoNiGa alloys have been receiving considerable interest due to their high temperature shape memory (SM) properties. While there have been many investigations on the mechanical and magnetic behavior of these materials, very little is known about the fundamental microscopic basis for the observed macroscopic behavior. In this work, we discuss the stability of CoNiGa-based structures. The austenite phase is modeled as fully-ordered L21 and as partially-ordered B2 (through the use of special quasi-random structures). The stability of the cubic austenite phase with respect to tetragonal distortions is examined and is concluded that the difference in energies between cubic and tetragonal variants is about 20 meV, consistent with the order of magnitude for the observed transformation temperatures. The instability of this structure is further investigated through the use of lattice dynamics and is concluded that the mechanism for the transformation is different from that of the much more studied and chemically similar Ni2MnGa SMA.

author list (cited authors)

  • Arroyave, R., Junkaew, A., Garay, A., Chari, A., Yao, C., & TMS, ..

publication date

  • May 2010