Microstructure And Properties Of Y₂O₃Dispersion Strengthened Fe-Cr-Al Sheet Prepared By EBPVD

Oxide Dispersion Strengthened (ODS) ferrite alloy is potential for the applicationto fuel cladding and structure material for fast breeder reactors of Generation Ⅳbecause of its excellent mechanics performance and resistance to irradiation at hightemperatures. As a new method for ODS alloy fabrication, Electron Beam PhysicalVapor Deposition (EBPVD) can elegantly solve the problem of the uneven distributionof oxide particles, and has unique advantages for the fabrication of large alloy sheets.This paper investigated yttria dispersion strengthened FeCrAl alloy sheets fabricatedby EBPVD technique, covering four aspects: the microstructural features ofas-deposited material; the effect of content of yttria on microstructure and mechanicalproperties of alloy sheets; strengthening processes of as-deposited alloy sheets;research on the electrochemical corrosion of as-deposited and treated sheets under3.5%NaCl solution. The investigation methods and main conclusions are summarizedin the following parts.X-ray diffraction (XRD) indicated that the matrix phase was α-[Fe,Cr], andrecrystal textures exisited in matrix. The microstructure of as-deposited material wascharacterized by means of scanning electron microscopy (SEM) and transmissionelectron microscopy (TEM).The results indicated that the sheets fabricated by EBPVDwere composed of equiaxed zone and columnar zone.The morphology of columnargrain depends on substrate rotation speed. The size and distribution of the poreslocated among columnar grains depends on substrate temperature and substraterotation speed. The size of yttria dispersoids lies between4~16nm.Investigations on the microstructure and mechanical properties of two sheetswith different yttria contents indicated that with the content of yttria increasing, thesize of matrix grains reduced while the size of yttria dispersoids increased, themicrohardness and strength of the sheets increased while the toughness decreased.Considering that the tensile properties at room temperature and elevatedtemperatures of as-deposited sheets were poor because of high porosity and lowdensity, high temperature annealing treatment, deformation processing through coldrolling and recrystallization treatment were performed to as-deposited sheets. Aftertreatments the tensile properties of the alloy sheets were enhanced. In combination with microstructure observation it can be asserted that the key of enhancing the tensileproperties of EBPVD alloy sheets is to improve its density through closing the pores asfar as possible, and gaining coarse crystalline grains is beneficial to tensile propertiesat elevated temperatures.Polarization curves indicated that ODS ferrite alloy prepared by EBPVD showedpassivation behavior and pitting features in3.5%NaCl solution. High temperatureannealing treatment can improve pitting corrosion resistance and uniform corrosionresistance of as-deposited materials. Through strengthen treatments the corrosionresistance of as-deposited materials was increased. Cold deformation and cristallisationtreatment lowed electrochemical polarization resistance, leading to worse uniformcorrosion properties. Cold deformation treatment with proper deformation andcrystallization treatment can improve the corrosion properties. Large grains andcompact microstructure were helpful to improve corrosion properties.