Materials Science and Engineering A273 – 275 (1999) 528 – 532 The influence of deformation on the microstructure and transformation temperatures of Fe–Mn–Si–Cr–Ni shape memory alloys G.J. Arruda a , V.T.L. Buono b, *, M.S. Andrade a a Fundac ¸a ˜o Centro Tecnolo ´gico de Minas Gerais -CETEC, A. J. Ca ˆndido da Sileira, 2000, CEP 31170 -000 Belo Horizonte, MG, Brazil b Departamento de Engenharia Metalu ´rgica e de Materiais, Uniersidade Federal de Minas Gerais, Rua Espı ´rito Santo, 35 Sala 206, 30160 -030 Belo Horizonte, MG, Brazil Abstract The characteristics of the martensitic transformation in a Fe–Mn–Si–Cr–Ni alloy and in a similar alloy containing also Co were investigated in terms of the amount and type of deformation: cold rolling, with 19 and 33% reduction of area, and wire drawing, with 20% reduction of area in the last pass. The temperatures of start and finish of the reverse transformations were measured by dilatometry. The constitution and microstructure of the alloys were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy and magnetic force microscopy. The cold forming processes applied to the alloys induced the formation of  and the   martensites, even when the start temperature of thermal martensite was well below room temperature. An increase of up to 500 K in the characteristic temperatures of the reverse transformation, when compared to thermal martensite, was also observed. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Martensitic transformation; Shape memory alloys; Fe – Mn based alloys; Deformation; Microstructure www.elsevier.com/locate/msea 1. Introduction The Fe–Mn–Si alloys are known to exhibit an excel- lent shape memory effect and have been the subject of many efforts to develop low cost shape memory materi- als [1–11]. Much of this effort has been directed to the improvement of the corrosion resistance of these alloys, leading to the development of Fe–Mn–Si–Cr–Ni al- loys [7–10] and of similar alloys containing also Co [11]. Various parameters such as alloy composition, ap- plied stress, prestrain, grain size, pre-existing martensite and thermal cycling, influence the shape memory effect in Fe–Mn–Si alloys, as summarized by Gu, Van Hum- beeck and Delaey [12]. In alloys containing Cr and Ni, the strain induced  (fcc) to  (hcp) martensitic transfor- mation is often accompanied by the  to  (bcc) or  to   transformations [13]. The presence of   martensite, formed during cooling or prestraining, is generally con- sidered as detrimental to the shape recovery process [12,14,15], although there is a recent report showing that the presence of a two phase microstructure of  and  , obtained by a suitable annealing process after deformation at room temperature, can improve the extent of shape recovery in an Fe-14Mn-5Si-9Cr-5Ni alloy [16]. The majority of the studies concerning the influence of straining on the microstructure and properties of these alloys consider only small deformation in tension, compression or bending. In this work, the aim was to investigate how the deformation by cold rolling and drawing would affect the microstructure and transfor- mation temperatures of previously annealed austenite in Fe–Mn–Si–Cr–Ni (–Co) alloys. 2. Experimental The two Fe–Mn–Si–Cr–Ni alloys investigated were prepared from high purity materials by induction melt- ing in argon gas atmosphere. The analyzed chemical compositions of the alloys are presented in Table 1. The * Corresponding author. Tel.: +55-31-238-1859; fax: +55-31-238- 1815. E-mail address: vbuono@gold.com.br (V.T.L. Buono) 0921-5093/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0921-5093(99)00393-7