Microstructure and tensile properties of Zr-containing ODS-FeCrAl alloy fabricated by laser additive manufacturing

Oxide dispersion strengthened (ODS) FeCrAl alloys have been considered as the promising candidate fuel cladding materials for the Gen-IV fission reactors due to excellent radiation tolerance, mechanical properties and corrosion resistance, but their manufacturing is complex process. Laser engineered net shaped (LENS) technology followed by post-build heat treatment was employed successfully to fabricate Zr-containing ODS-FeCrAl alloy. The microstructure of as-deposited and heat-treated alloys was characterized by optical microscope (OM), electron backscatter diffraction (EBSD), scanning electron microscope (SEM) and high-resolution transmission electron microscope (HRTEM). The tensile tests were carried out at room temperature. The results show that the coarse columnar grains with preferred orientation ([001] fibre texture) are obtained after LENS deposit and are remained after post-build heat treatment. The average width of columnar grains for both as-deposited and heat-treated samples is similar to 180-190 mu m. A slag-like layer which is made up of Y3Al5O12, ZrO2 and Al2O3 is observed at the surface of deposited sample. Some coarse appendage oxides which consist of Al2O3 and Y4Zr3O12 are distributed in the matrix of as-deposited sample. Post-build heat treatment produces high-density nanoscale Y4Zr3O12 oxides in the matrix. The formation mechanism of different type oxides is explained. Both as-deposited and heat-treated samples present anisotropic tensile properties. After post-build heat treatment, the tensile strength is improved significantly by the formation of high-density nanoscale Y4Zr3O12.