Mössbauer spectroscopy and Rietveld refinement used to analyze stainless steel properties regarding shape memory effect (SME)

ABSTRACT

The resonant absorption of recoilless g-rays, known as Mössbauer Spectroscopy, is an efficient nuclear prospecting technique to structural and magnetic analysis. When studying steels, it is possible to accurately analyze the surface of materials using the Conversion Electron Mössbauer Spectroscopy technique (CEMS) that evaluates the sample’s surface to a depth of 200 nm, and by Conversion X-ray Mössbauer Spectroscopy by (CXMS), which can go deeper and investigate inner layers of steel samples (10 mm). In this work, this technique was employed to study the crystallographic reversion (f.c.c.àh.c.p.) of stainless steel shape memory. A hexagonal martensitic phase was induced mechanically through the compression test and the reversion to austenite phase was observed using heat treatment. Mössbauer spectroscopy measurements were carried out using the conversion of electrons, and X-ray with a ⁵⁷Co source in a rhodium matrix at room temperature and without the external fields. Spectra were analyzed using specific adjustment software. The results indicated great reversal of e-martensite. Rietveld refinement analysis was obtained using the XRD data to evaluate possible structural changes occurring during the thermo-mechanical treatment (cycles of deformation followed by heating). Comparison of the Mössbauer spectra and Rietveld refinement are important for understanding the reversal of the martensitic phase. In this case, the crystal structure changes resulted in a shape recovery material, which was deformed beyond its elastic limit.

Keywords
Shape memory effect; stainless steel; ?-martensite,; Mössbauer Spectroscopy; Rietveld refinement