Abstract
Abstract Self-assembly due to phase separation within a miscibility gap is important in numerous material systems and applications. A system of particular interest is the binary alloy system Fe-Cr, since it is both a suitable model material and the base system for the stainless steel alloy category, suffering from low-temperature embrittlement due to phase separation. Structural characterization of the minute nano-scale concentration fluctuations during early phase separation has for a long time been considered a major challenge within material characterization. However, recent developments present new opportunities in this field. Here, we present an overview of the current capabilities and limitations of different techniques. A set of Fe-Cr alloys were investigated using small-angle neutron scattering (SANS), atom probe tomography, and analytical transmission electron microscopy. The complementarity of the characterization techniques is clear, and combinatorial studies can provide complete quantitative structure information during phase separation in Fe-Cr alloys. Furthermore, we argue that SANS provides a unique in-situ access to the nanostructure, and that direct comparisons between SANS and phase-field modeling, solving the non-linear Cahn Hilliard equation with proper physical input, should be pursued.
Highlights
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]
We present new small-angle neutron scattering (SANS) measurements and analysis, conducted using a pulsed neutron source and the time-offlight technique, which allows the detection of phase separation over a wide range of length scales simultaneously, and compare these results with our prior measurements using transmission electron microscopy (TEM) and atom probe tomography (APT).[17,29,32]
The patterns of solution treated samples have no clear peak. They are flat in the Q range larger than 0.1 A À1 and they almost overlap with each other (Figure 1(d))
Summary
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] 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. 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]
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