Volume 12, Number 1, December - 2003 - ACTA MICROSCOPICA 99 ARTICLE Stainless Shape Memory Alloys Microstructure Analysis by Optical Microscopy Using Different Etchants Fabiana C. Nascimento (1,2) ; Flávio V. Sorrila (1) ; Jorge Otubo (1,3) and Paulo R. Mei (1) 1 DEMA/FEM, State University of Campinas, 13083-970, Campinas, SP, Brazil; fabcris@ifi.unicamp.br 2 Applied Physics Department, Gleb Wataghin Physics Institute, State University of Campinas, 13083-970, Campinas, SP, Brazil. 3 ITA – Technological Institute of Aeronautics 2228-900, São José dos Campos, SP, Brazil. Introduction Some Fe-Mn-Si based alloys exhibit shape memory effects (SME) which is originated by the γ(fcc)↔ε(hcp) martensitic transformation. The Fe-Mn-Si-Cr-Ni-Co alloys present a good property of corrosion resistance and the shape memory properties of these alloys appear to depend upon the microstructure of the austenitic state [1-3] . To improve the shape memory effect a special thermomechanical treatment called training is applied. It consists in a deformation (by compression or tensile test) at room temperature to induce the mechanical ε-martensite and then anneal at temperature above A F to revert ε(hcp)→γ(fcc) [4] to recover the shape. Repeating this cycle several times can improve SME up 50%. To follow the microstructure evolution during thermomechanical cycling is very important because it changes as the cycling proceeds. In this work, optical microscope observations of γ phase and ε- martensite in the Fe-Mn-Si-Cr-Ni-Co based alloys are described by using different etchants. There are several papers in the literature that present many types of etchants for this kind of alloy [1,2,4-5] . Our main objective was to compare some etchants used for these type of alloy and to select the best one to follow the martensitic transformation associated with the thermomechanical treatment. Materials and Methods The chemical compositions (in wt.%) of alloys A and B used in this work are listed in Table 1. Table 1. Chemical composition shape memory stainless alloys A and B (wt.%). Elements (wt.%) Alloy A Alloy B C 0.0044 0.09 Si 5.11 5.25 Mn 7.79 8.26 P 0.003 0.02 S 0.007 0.06 Co 11.85 11.84 Cr 13.02 12.81 Ni 5.74 5.81 Mo 0.01 0.01 Cr 0.31 0.16 The ingots were produced by conventional vacuum induction melting (VIM), hot rolling (1473K) and after Abstract The use of etchant to study the evolution of ε- martensite on the stainless shape memory alloys (SME) it’s very important because the correct choice of etching can result not only on the identification of these phases as also in a quantitative analysis. In this work we presented some options of etchants that can be used to study the changes on the microstructure before and after the thermomechanical treatment. Using Fe-Mn-Si-Cr-Ni-Co alloys with different grains size as initial condition submitted at six- thermomechanical treatment, three etchant types are testing for analyse the γ(fcc)↔ε(hcp) martensitic transformation. The preliminary result shows that the color etching method is the more indicate to revel the stress-induced martensite, because such phase is reveled with a color. But, for such condition (chemical composition, volume fraction of phases, grain size) the composition etching will be adapted. Keywords: Stainless shape memory alloys, ε- martensite, thermomechanical treatment, martensitic transformation.