Effect Of Ti And Zr On Microstructure And Properties Of Nano-structured 9Cr-ODS Steels

Nano-structured oxide dispersion strengthened(ODS)steels are regarded as the promising structural materials for the first wall/blanket applications in fusion reactors because of their excellent irradiation tolerance,helium embrittlement resistance and improved high temperature strength.These superior properties come mainly from ultra high-density of nano-precipitates and fine grain size in ODS steels.In this study,mechanical alloying(MA)and hot isostatic pressing(HIP)were used for preparing 9Cr-ODS steels(9Cr-Y2O3、9Cr-Zr、9Cr-Ti、9Cr-Ti-Zr).The microstructure of the ODS steels,such as the grain size and grain morphology,types,density and size of nano-size precipitates were studied by SEM,EBSD,TEM,HRTEM.Hardness and tensile properties were tested.The following conclusions were obtained:(1)The effect of Ti and Zr on the relative densities of 9Cr-ODS steels is negligible.The relative densities of four ODS steels are all more than 98%.(2)The average grain sizes of four 9Cr-ODS steels are 0.57μm(9Cr-Ti-Zr ODS steel),0.68μm(9Cr-Ti ODS steel),0.81μm(9Cr-Zr ODS steel)and 1.2μm(9Cr-Y2O3 ODS steel),respectively.This means that the addition of Ti and Zr sufficiently reduces the average grain size.(3)The addition of Ti/Zr can influence the types,size and density of nano-size precipitates.In 9Cr-Y2O3 ODS steel,the average size of precipitates is the largest(4.75nm)and the density is the lowest(6.2×1022/m3).In 9Cr-Ti-Zr ODS steels,however,the average size of precipitates is the smallest(3.09nm),and the density is the highest(1.2×102/m).This means that the addition of Ti and Zr sufficiently reduces the average size of precipitates and increases the density of precipitates.(4)The tensile strength decreases and the total elongation increases with the increasing test temperature before 600℃.The 9Cr-Ti-Zr ODS steels exhibits the highest strength at room and high temperature tensile test.The fracture mechanism is changing from mixed brittle and ductile fracture to ductile fracture with increasing the temperature.