Structural Characterization of Phase Separation in Fe-Cr: A Current Comparison of Experimental Methods
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STAINLESS steels, which are based on the Fe-Cr binary alloy, are widely used in industrial applications because of their good mechanical properties and excellent corrosion resistance.[1] However, ferrite- or martensite-containing stainless steels may undergo phase separation, via either nucleation and growth (NG) or spinodal decomposition (SD), and form Fe-rich (a) and Cr-rich domains (a¢) when they are thermally treated within the miscibility gap. Phase separation increases the hardness but decreases the impact toughness of the alloys, which could cause unexpected fracture in applications. Since alloys prone to this embrittlement are currently used in, for example, nuclear power generation and are being considered for new nuclear power
XIN XU, Ph.D. Student, and JOAKIM ODQVIST and PETER HEDSTRO¨M, Associate Professors, are with the Department of Materials Science and Engineering, KTH Royal Institute of Technology, 100 44 Stockholm, Sweden. Contact e-mail: [email protected], [email protected] MAGNUS HO¨RNQVIST COLLIANDER and MATTIAS THUVANDER, Associate Professors, are with the Department of Physics, Chalmers University of Technology, 412 96 Go¨teborg, Sweden. AXEL STEUWER, Professor, and JOHAN E. WESTRAADT, Senior Researcher, are with the Nelson Mandela Metropolitan University, Gardham Avenue, Port Elizabeth 6031, South Africa. STEPHEN KING, Principal Research Scientist, is with the ISIS Facility, Rutherford Appleton Laboratory, Didcot OX11 0QX, UK. Manuscript submitted March 31, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
plants,[2] brittle fracture must be avoided. The embrittlement phenomenon is known as ‘‘475 C embrittlement’’ and, for instance, it limits the application temperature of duplex stainless steels to about 523 K (250 C).[3] Due to the high technical relevance and its suitability as a model material for phase separation studies, binary Fe-Cr alloys have been extensively investigated. Theoretical tools such as phase-field modeling[4–6] and kinetic Monte Carlo[7–10] are frequently adopted to simulate the nanostructure evolution, and experimental tools such as Mo¨ssbauer spectroscopy (MS),[11–14] transmission electron microscopy (TEM),[4,5,15–17] small-angle neutron scattering (SANS),[18–25] atom probe field ion microscopy (APFIM),[7–9,26,27] and later atom probe tomography (APT)[10,28–34] have been applied. Most of the studies in the literature focus on the rather late stages of phase decomposition, when the embrittlement is already severe, and today it is still considered a major challenge to quantitatively characterize the nanostructure in technically relevant cases, when the length-scale is in the order of a few atomic distances and the concentration variations between a and a¢ are only a few atomic percent.[3,27,35] The purpose of the present work is to compare and discuss currently available experimental methodologies for structural characterization of phase separation in Fe-Cr alloys. In prior work, some of the present authors have presented APT and TEM studies of phase
separation in binary
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