Characterization of phases in an Fe-Mn-Si-Cr-Ni shape memory alloy processed by different thermomechanical methods

V. FUSTER; A. DRUKER; A. BARUJ; J. MALARRÍA; R. BOLMARO

MATERIALS CHARACTERIZATION

ELSEVIER SCIENCE INC

Lugar: Amsterdam; Año: 2015 vol. 109 p. 128 - 137

1044-5803

The presence of second phases in FeMnSi based systems have been widely discussed in theliterature, and also in our previous works. In this manuscript, various specimensof an Fe-15Mn-5Si-9Cr-5Ni mass % (nominal composition)shape memory alloy were processed bydifferent thermomechanical treatments in order to identify the phases presentin each condition. TEM-EDS results indicate that the chemicalcomposition of the second phase we found in all cases is close to 20Mn-xSi-12Cr-4Nimass %, with x varying between 10 and 21, and Fe balance. This is compatiblewith an Fe5Ni3Si2 typeintermetallic phase. It forms in a temperature range between 650 and 900 °C, independentlyof the thermomechanical processing and the coexisting phases. Rietveldrefinement of X-ray patterns was done using MAUD software, and the phase wasfound to be isostructural to the Ni5Cr3Si2 p-phasewith space group P213 and latticeparameter equal to 0.6227(7) nm. Phase quantification, crystallite diameter andaccumulated microstrain were also computed as a convenient set of variables,necessary for improving refinement quality. Relevant microstructuralinformation, i.e. stacking fault and twinning probabilities, along withdislocation density, were calculated for austenite, the matrix phase,contributing to the reliability of the determinationof the crystallographic characteristics of the second phase.