ON THE ROLE OF TIN SOLUBILITY IN THE PRECIPITATION OF THE SIGMA-PHASEIN FE-CR-SN ALLOYS

The maximum solubility of tin in iron-chromium alloys with near equiat omic compositions was studied using scanning and transmission electron microscopy together with Mossbauer spectroscopy. In as-cast alloys wi th tin contents of 2 and 5 at%, tin decorates the nucleation sites of sigma-phase precipitating along grain boundaries, edges and corners. W hen the alloys are annealed at 900 degrees C. tin diffuses into the ma trix, precipitating again, still concentrating in grain edges and corn ers. Vickers hardness values and lattice parameters of Fe-Cr-Sn alloys vary linearly with tin concentration up to 2 at% confirming the limit of solubility of tin in these alloys. The presence of the beta-Sn pha se was found in the samples by Sn-119-site Mossbauer spectroscopy at 1 60 K and transmission electron microscopy at room temperature.