Study On Nano-scale Precipitates Of 9Cr-ODS Steels

Nano-structured ODS steels exhibit excellent radiation tolerance and high temperature mechanical properties due to high density of nanoscale precipitates,submicron grain size and high-density of dislocations.Therefore,the ODS steels are considered to be the leading candidate materials for fusion reactor first wall/blanket application.The chemical composition and consolidation condition can influence significantly the types and distribution characteristics of nanoscale precipitates,then influence irradiation properties and mechanical properties of ODS Steels.In this study,the alloy powders with the addition of Ti,Zr,Ti + Zr elements were heat-treated to simulate the consolidation process of ODS steels.The types of nanoscale precipitates were studied by using XAFS and XRD.And the effects of annealing time on the size and density distribution of nanoscale precipitates were analyzed using SAXS techniques.The relationship of hardness and nanoscale precipitates in different ODS steel alloy powders were studied.The following conclusions were obtaied:1.The addition of Ti and Zr elements can influence significantly the type of nanoscales precipitates in 9Cr-ODS steels.The precipitates are Y2O3 and Cr2O3 in the 3Y(Fe-9Cr-1.5W-3Y2O3)sample;Y2O3 is replaced by Y2Ti2O7 in 3Ti(Fe-9Cr-1.5W-3Ti-3Y2O3)sample;Y4Zr3O12 and ZrO2 in 3Zr(Fe-9Cr-1.5W-3Zr-3Y2O3)sample;Y2Ti2O7,Y4Zr3O12 and ZrO2 in 3Ti3Zr(Fe-9Cr-1.5W-3Ti-3Zr-3Y2O3)sample.2.The nanoscale precipitates in ODS steels are formed during annealing process,and the density of the nanoscaled precipitates increases with the increasing of the annealing time,then decreases gradually.The density of nanoscale precipitates reaches to the maximum value after 0.5h annealing in the Ti-containing ODS steels,and the value reaches to the maximum at Ih in the Ti-free ODS steels,indicating that Ti can promote the formation of nanoscale precipitates.The change of the size of nanoscale precipitates in the ODS steels is opposite.3.The hardness of mechanical alloying powders is the highest due to work hardening and grain refinement.After heat treatment,the hardness decreases.4.Both Ti and Zr elements can promote mechanical properties.The effects of Ti on mechanical properties is more obvious than Zr because the size of rich Y-Ti-O precipitates is smaller than Y-Zr-O precipitates and the density of rich Y-Ti-O precipitates is higher than Y-Zr-O precipitates.The mechanical properties can be further improved by adding both Ti and Zr.