Microstructure And Mechanical Properties Of Low Cr/High Al Oxide Dispersion Strengthened FeCrAl Alloys

Oxide dispersion strengthened(ODS)FeCrAl alloys,which are considered to be one of the important candidate materials for the Generation IV fission reactors especially fast reactor fuel cladding,contain high-density nano oxides,high-density dislocation and sub-micron size grains,resulting in excellent high-temperature mechanical properties,excellent radiation and corrosion resistance.High Cr ODS-FeCrAl alloys can generate Cr-rich brittle phase under high temperature and irradiation conditions,which makes the material produce aging brittleness and irradiation brittleness.Therefore,the development of low Cr and high A1 ODS alloy has attracted more and more attention.In this study,seven kinds of low Cr and high Al ODS-FeCrAl alloys were prepared by mechanical alloying(MA)and hot isostatic pressing(HIP)methods,including 5Cr-xAl(x=4.5,5.0,5.5,6.0 wt%)ODS alloys and yCr-6.0Al(y=5,9,12,15 wt%)ODS alloys.The effects of Cr and Al contents on microstructure and mechanical properties of the ODS alloys were studied by SEM,EBSD and TEM.The following research conclusions are obtained:(1)50 h mechanical alloying produced supersaturated alloy powders.The addition of Al and Cr does not change obviously the average particle size of MA powders.(2)In 5Cr-xAl ODS alloys,the large oxides(>20 nm)are mainly Al2O3.The content of Al has a significant effect on the average diameter and number density of the large oxides.With the increasing of Al content,the average diameter of large oxides is 37.4 nm,38.6 nm,42.6 nm and 45.9 nm,while the number density is 1.4×1020/m3,2.0×1020/m3,2.6×1020/m3 and 3.4×1020/m3,respectively.In yCr-6.0Al ODS alloys,with the increasing of Cr content,the average diameter of the large oxides is not changed significantly,but the number density of the large oxides decreases,which is 3.4×1020/m3,2.5×1020/m3,2.4×1020/m3,2.0×1020/m3,respectively.(3)The nano(<20 nm)oxides in seven kinds of low Cr and high Al ODS-FeCr-Al alloys are mainly Y4Zr3O12 and Y2TiO5,together with a few Y3Al5O12.In 5Cr-xAl ODS alloys,with the increasing of Al content,the average diameter of the nano oxides is 5.3 nm,5.6 nm,6.0 nm and 6.3 nm,respectively.With the increasing of Al content,its number density increases first and then decreases.The number density of nano oxides in 5Cr-5.5Al alloy is the largest,i.e.4.7×1022/m3.In yCr-6.OAl ODS alloys,with the increasing of Cr content,the average diameter of the nano oxides is 6.3 nm,6.5 mm,6.4 nm and 6.6 nm,and the number density is 2.9×1022/m3,3.1×1022/m3.3.7×1022/m3,4.3×1022/m3,respectively.(4)In 5Cr-xAl ODS alloys,with the increasing of Al content,the average grain size of ODS alloys decreases first and then increase,which is 1.64 ?m,1.33 p?m,1.21 ?m and 2.44?m,respectively.The grain size of 5Cr-5.5Al ODS alloy reaches the minimum value of 1.21?m.In yCr-6.0Al ODS alloys,with the increasing of Cr content,the average grain size of ODS alloys decreases all the time,which is 2.44 ?m,0.99 ?m,0.87 ?m and 0.72 ?m.Among which the grain size of 5Cr-6.0Al alloy is the largest,and the grain size of 15Cr-6.0Al alloy is the smallest.(5)In 5Cr-xAl ODS alloys,with the increasing of Al content,the average hardness value is increase first and then decreases.The hardness values are 381 HV,412 HV,446 HV,441 HV,respectively.In yCr-6.0Al ODS alloy,the Cr element has the effect of improving the hardness of the ODS alloy,the average hardness value is 441 HV,487 HV,492 HV and 569 HV,respectively.(6)The seven low Cr/high Al ODS alloys show excellent tensile strength at room temperature.In 5Cr-xAl ODS alloys,with the increasing of Al content,the tensile strength of ODS alloy at room temperature increases first and then decreases(1209 MPa,1273 MPa,1417 MPa and 1148 MPa,respectively),and the elongation is 12.4%,9.6%,8.6%and 8.1%,respectively.5Cr-xAl ODS alloys have excellent tensile strength and elongation at 600?;The tensile strength of ODS alloys at 700? increases with the increasing of Al content.The tensile strength of the 5Cr-6.0Al alloy at 700? is maximum(539 MPa).In yCr-6.0Al ODS alloys,with the increasing of Cr content,the tensile strength at room temperature is 1148 MPa,1222 MPa,1253 MPa and 1386 MPa,respectively.And the tensile strength at high temperature decreases first and then increases with the increasing of Cr content.The tensile strength of ODS alloy at 600? is 647 MPa,589 MPa,538 MPa,890 MPa,respectively.The tensile strength of ODS alloy at 700? is 539 MPa,451 MPa,416 MPa,587 MPa,respectively.