Study On The Hardening Effect Of ODS Steels After Helium Implantation

With the development of nuclear energy,research on the reactor structural materials is getting more important.Irradiation hardening which is generally accompanied by loss of fracture toughness of materials has attracted increasing attention.Helium can inevitably be produced via(n,?)reaction and accumulate in structural components in fast breeding reactors on in fusion reactors.ODS steels,as one of the candidate structure materials for reactors,is widely studied.In the present study,effects of helium bubbles on irradiation hardening in ODS ferritic steels were studied.Specimens of two ODS ferritic steels(16Cr-0.1Ti and 15Cr-4Al-0.6Zr-0.1Ti)were implanted with mutiple-energy He ions so that a damage plateau with an average displacement damage of 0.42 dpa and an average He concentration of 7000 appm was formed from the near surface to a depth about 1 micrometers.The specimens were subsequently annealed at 800? for 1 hour in vacuum so that dislocation loops with a high density in the as-implanted state underwent rapid growth and coalescence meanwhile helium bubbles at nano-scale were formed.Nano-indentation test was taken to obtain the nano-hardness of specimens.Microstructures of the specimens after irradiation/annealing were investigated with transmission electron microscopy(TEM).Some helium bubbles were generally located at oxide/matrix interfaces,dislocations and grain boundaries.By using the dispersed barrier strength model,the strength factor of helium bubbles in two ODS steels 16Cr-0Al-0.1Ti and 15Cr-4Al-0.6Zr-0.1Ti is estimated to be 0.7 and 0.26,respectively.The discrepancy of pressures in bubbles may account for the divergence of the strength factors in the two ODS steels.If take the dislocations in ODS steel 15Cr-4Al-0.6Zr-0.1Ti into consideration,the strength factor is estimated to be between 0.1 and 0.26,which is close to that of helium bubbles in austenitic steels in previous studies.