Local configurations and atomic intermixing in as-quenched and annealed Fe_1−xCr_x and Fe_1−xMo_x ribbons

Abstract

Local atomic configuration, phase composition and atomic intermixing in Fe-rich Fe_1−xCr_x and Fe_1−xMo_x ribbons (x = 0.05, 0.10, 0.15), of potential interest for high-temperature applications and nuclear devices, are investigated in this study in relation to specific processing and annealing routes. The Fe-based thin ribbons have been prepared by induction melting, followed by melt spinning and further annealed in He at temperatures up to 1250 °C. The complex structural, compositional and atomic configuration characterisation has been performed by means of X-ray diffraction (XRD), transmission Mössbauer spectroscopy and differential scanning calorimetry (TG-DSC). The XRD analysis indicates the formation of the desired solid solutions with body-centred cubic (bcc) structure in the as-quenched state. The Mössbauer spectroscopy results have been analysed in terms of the two-shell model. The distribution of Cr/Mo atoms in the first two coordination spheres is not homogeneous, especially after annealing, as supported by the short-range order parameters. In addition, high-temperature annealing treatments give rise to oxidation of Fe (to haematite, maghemite and magnetite) at the surface of the ribbons. Fe_1−xCr_x alloys are structurally more stable than the Mo counterpart under annealing at 700 °C. Annealing at 1250 °C in He enhances drastically the Cr clustering around Fe nuclei.

Keywords:

• Fe-based alloys
• Mössbauer spectroscopy
• thermal analysis
• atomic intermixing
• local atomic configurations
• short-range order parameters

Acknowledgements

This work was supported by the Romanian National Program, Core Program 2016–2018 (PN16-480102) at NIMP. The financial support of the Romanian Ministry of Education through projects PN-II-PT-PCCA-2013-4-0971 (contract no. 275/2014) and POC P_37_697 REBMAT (contract 28/01.09.2016) are also highly acknowledged.