Influence of mechanical alloying and extrusion conditions on the microstructure and tensile properties of Low-Cr ODS FeCrAl alloys

• Published in: Journal of nuclear materials Vol. 512; no. C; pp. 227 - 238
• Main Authors: Massey, Caleb P., Dryepondt, Sebastien N., Edmondson, Philip D., Terrani, Kurt A., Zinkle, Steven J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-12-2018; Elsevier BV; Elsevier
• Subjects: Alloy development; Alloy powders; Alloying elements; Alloys; Atomizing; Ball milling; Chemical precipitation; Chromium; Cladding; Dispersion hardening alloys; Ductility; Energy transmission; Extrusion; Ferrous alloys; Grain size; High strength alloys; High temperature; Hot extrusion; Light water reactors; MATERIALS SCIENCE; Mechanical alloying; Mechanical properties; Microstructure; Nuclear fuels; Nuclear reactors; Oxidation; Oxide dispersion strengthened (ODS) alloy; Oxide dispersion strengthening; Oxides; Particle size; Powder; Precipitation; Reactors; Scanning electron microscopy; Spectroscopy; Strengthening mechanisms; Superposition (mathematics); Temperature effects; Tensile properties; Tensile strength; Transmission electron microscopy; Mechanical properties; Precipitation; Strengthening mechanisms; Oxide dispersion strengthened (ODS) alloy
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2018.10.017

Low-chromium (<10%Cr) high strength oxide dispersion strengthened (ODS) FeCrAl alloys are considered promising candidates for accident tolerant fuel cladding in light water fission reactors. These alloys are designed to combine the beneficial high temperature mechanical properties of ODS materials with the exceptionally high temperature oxidation resistance of FeCrAl in comparison to conventional Zr-containing cladding materials, while also providing good mechanical and aqueous corrosion behavior under normal light water reactor operating conditions. The initial (1st generation) ODS FeCrAl alloys combined gas atomized FeCrAl powders with yttria and other oxides for alloying element additions using the mechanical alloying approach. These alloys exhibited low ductility but excellent high temperature tensile strength while maintaining good oxidation resistance at temperatures up to 1400 °C. In an attempt to improve alloy ductility for accident tolerant fuel cladding applications, new low-Cr ODS FeCrAl alloys with decreased oxygen content were developed with the Zr alloying solute already gas atomized into the powder prior to mechanical alloying. The resultant Fe-10Cr-6.1Al-0.3Zr+0.3Y2O3 (106ZY) powders were ball milled for 10, 20, and 40hr followed by consolidation via hot extrusion at temperatures ranging from 900 to 1050 °C. Increasing the mechanical alloying time decreased the resultant grain size and improved high temperature tensile properties. Decreasing the extrusion temperature refined the grain size and subsequently strengthened the ODS FeCrAl 106ZY alloys while lowering the ductility. Scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) demonstrated the Zr solute addition effectively sequestered impurity C and N within the matrix. The root mean square (RMS) hardening superposition model for yield strength shows good agreement with experimental results. Errors between predicted and experimental values are discussed within the scope of processing parameters. These 2nd generation 106ZY alloys show a distinct increase in alloy ductility without sacrificing the high temperature tensile properties characteristic of legacy or 1st generation ODS FeCrAl alloys.
•10Cr ODS FeCrAl alloys exhibit higher ductility than 12Cr alloys with higher oxygen content.•Zr solute additions sequester impurity C and N added during alloy fabrication.•Alloy strengthening is well described through the root mean square (RMS) superposition model.