Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Microstructural evaluation and mechanical behaviour of dissimilar niti- stainless steel joints welded by micro gas tungsten arc welding M.J.C. Oliveira a,* , R.H.F. Melo b , T.M. Maciel c , C.J. de Araújo c a Industry Unit, Instituto Federal de Educação, Ciência e Tecnologia do Ceará, IFCE campus Sobral, Brazil b Industry Academic Unit, Instituto Federal de Educação, Ciência e Tecnologia da Paraíba, IFPB, Brazil c Mechanical Engineering Academic Unit, Universidade Federal de Campina Grande, UFCG, Brazil HIGHLIGHTS • Dissimilar NiTi-AISI 304 joints were welded by micro GTAW. • The joints' mechanical behaviour is influenced by Inconel 625 use. • The M25IC welded joint presented a UTS of 286 MPa and elongation of 4.5%. GRAPHICAL ABSTRACT ARTICLE INFO Keywords: NiTi Shape memory alloys Dissimilar welding Metallurgy ABSTRACT In this work, the microstructure and mechanical behaviour of dissimilar nickel-titanium (NiTi) shape memory alloy (SMA) and AISI 304 stainless steel (SS) thin sheets welded by micro gas tungsten arc welding (GTAW) using NiTi and Inconel 625 as filler metals were studied. The influence of a post-weld heat treatment was also elu- cidated. The obtained dissimilar NiTi-304SS joints were characterized by optical and scanning electronic mi- croscopy, tensile tests and the Vickers hardness. After welding, the joints exhibited a heterogeneous weld zone due to the formation of intermetallic elements along with embrittlement of the weld metal. For non-heat treated joints, partial diluted zones with distinct morphology, chemical composition and hardness were formed. It was possible to increase the mechanical strength of the joint up to 286 MPa by using an intermediate layer of Inconel 625 at the junction between dissimilar metals and by applying heat treatment for stress relief. 1. Introduction Shape memory alloys (SMA) are a special and unique class of me- tallic materials with the ability to change their shape under plastic deformation and then revert to the original shape when temperature is increased, different from conventional structural metals. The origin of this phenomenon is a reversible thermoelastic martensitic transforma- tion. This martensitic phase transformation can be induced in specific conditions for both mechanical and thermal loads [1,2]. There are several types of SMA: nickel-titanium based alloys (NiTi), copper-based alloys and iron-based alloys [2]. However, NiTi SMA are the most commonly studied and used due to their excellent resistance to corrosion and fatigue as well as wider transformation temperature range (-100 °C to +200 °C) that allows applications at different temperatures. Due to its excellent mechanical properties, good corro- sion resistance and biocompatibility, as well as the best functional shape memory effect and superelasticity properties, the NiTi SMA and its ternary variations have been studied for various applications in different areas. This exclusive behaviour of NiTi SMA has enabled the development of innovative applications in the medical, dental, aerospace, auto- motive, automation and control, power, chemical processing, heating https://doi.org/10.1016/j.matchemphys.2018.12.013 Received 13 March 2017; Received in revised form 1 November 2018; Accepted 10 December 2018 * Corresponding author. E-mail address: matheus.oliveira@ifce.edu.br (M.J.C. Oliveira). Materials Chemistry and Physics 224 (2019) 137–147 Available online 11 December 2018 0254-0584/ © 2018 Elsevier B.V. All rights reserved. T