Title:	First-principles study of ferrous shape memory alloys
DNr:	SNIC 2014/1-129
Project Type:	SNIC Medium Compute
Principal Investigator:	Börje Johansson <borje.johansson@fysik.uu.se>
Affiliation:	Kungliga Tekniska högskolan
Duration:	2014-05-01 – 2015-05-01
Classification:	20506
Keywords:

Abstract

Normally in metallic materials, the elastic strain is limited to 0.2%. The so-called ''superelasticity´´ for ''pseudoelasticity´´ with elastic strain up to around 10% relies on the occurrence of a thermoelastic martensitic phase transformation. Fe-based shape memory alloys have long been investigated, because of their better workability and low cost. They are commercially more attractive than NiTi-based SMAs. The invention of ferrous shape memory alloy Fe-28Ni-17Co-11.5Al-2.5Ta-0.05B by Y. Tanaka et. al is a breakthrough, in which alloy the elastic strain reaches ~13%. However, the mechanisms of achieving super-elasticity in ferrous shape memory alloys, mainly in the FeCoNiAlTaB and relative systems have not been well understood. For examples, there is large discrepancy between theoretical transformation strains and the experimentally observed values in both sinlge and poly crystallines. In this project, we will investigate the phase stability, bain tranformation, fcc/L12 interface structure and magnetic properties, etc., to gain information from ab initio calculations to shield light on understanding the mechanisms of the high plastic strain.